Wake Turbulence • Tomahawk • Airframe Icing · R22 and R44 of Helicopter Training College Ltd,...

Pointing to Safer Aviation

1997, Issue 3

• Wake Turbulence • Tomahawk • Airframe Icing

21997, Issue 3 VECTOR

C O N T E N T S

ISSN 1173-9614

Page 3 Safety SeminarsWe urge you to attend whichevertype of seminar is close to ormost convenient for you.

Next IssueOur publications are next scheduled to bein your letterbox in early August 1997.

Cover PhotographsR22 and R44 of Helicopter Training College Ltd, over the environs of Auckland.Photographs taken by John King for Helicopter Training, and provided to us bycourtesy of the Company CFI, Ray Wilson.

Ice Cloud

Freezing g Temperature

Page 4 How to Avoid Wake TurbulencePilots should remember threebasic warnings concerning waketurbulance.

Page 11 It Can Happen!“I’ve survived this crash, and nowI’m going to drown...”

Page 13 The Trusty TomahawkAll aircraft have differenttraits, and the Tomahawk is noexception.

Page 17 Cessna OwnersThe pilot … was taken by surpriseand pulled both the controlcolumn and the throttle aft withhim.

2 Ice TooThe commander was surprised bythe significant reduction inperformance for a relatively smallamount of ice accretion.

Editor: Cliff Jenks

Assistant Editors: Pam Collings,Clare Jeeves, Mike Woods

Design and Typesetting: Perception

Published by: Civil Aviation Authority ofNew Zealand, P O Box 31-441,Lower Hutt, NEW ZEALAND.

Telephone +64-4-560 9400Fax +64-4-569 2024Editor Internet: [email protected] published eight times a year.

Publication Content

The views expressed in Vector are those of theEditor or the named contributor. They areintended to stimulate discussion and do notnecessarily reflect the policy of the Civil AviationAuthority. Nothing in Vector is to be taken asoverriding any New Zealand Civil Aviationlegislation, or any instructions issued orendorsed by the Civil Aviation Authority of NewZealand.

Reader comments and contributions arewelcome and will normally be published, but theEditor reserves the right to edit or abridge them,and not to publish those that are judged not tocontribute constructively towards safer aviation.Reader contributions and correspondenceregarding the content of Vector should beaddressed to: Vector Editor, PO Box 31-441,Lower Hutt.

Distribution

Vector is distributed automatically to NewZealand Flight Crew and Aircraft MaintenanceEngineer licence holders, to most organisationsholding an Aviation Document, and to certainother persons and organisations interestedin promoting safer aviation. Vector articlesalso appear on CAA’s website at http://www.caa.govt.nz/

Vector is available on subscription only fromPublishing Solutions Ltd, P O Box 983,Wellington, freephone 0800 800 359, phone+64–4–471 0582, fax +64–4–471 0717.

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Readers receiving Vector free of charge shouldnotify the Civil Aviation Authority (ApprovalsClerk) of any change of address; quoting yourCAA Client Number (or licence number) willassist in administration. Paying subscribersshould notify Publishing Solutions Ltd.

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Reproduction in whole or in part of any item inVector, other than material shown to be fromother sources or named authors, is freelypermitted, providing that it is intended solelyfor the purpose of promoting safer aviation, andproviding that acknowledgment is given toVector.

Page 10 Introducing Taupo UNICOM“Taupo UNICOM” has beendeveloped to meet some of thesafety recommendation needs.

An AFIS ...

A UNICOMservice ...

Page 18 New Problems with IceInflight icing has always been aproblem for aircraft, but recentlythe scope and intensity of thatproblem have expanded.

31997, Issue 3VECTOR

This year’s series of Safety Seminars isabout to begin.

The theme is “Pressures on Pilots”, butsimilar pressures are, of course,experienced by others in the aviationindustry, and you don’t have to be apilot to attend. In addition, while eachof the fixed-wing and rotary-wingseminars will have a slant towards thoseparticular types of operations, they areopen to all. And, not just pilots – youmay be an engineer, non-flyingmanager or connected in some otherway to the aviation industry. Theseseminars will be of benefit to all inthe aviation industry – we urge you toattend whichever type of seminar isclose to or most convenient for you.

The presenters are all experienced andrespected pilots from the New Zealandaviation industry who, with the supportof CAA, are giving their time, expertiseand wisdom to help make a differenceto aviation safety. They will be able togive simple and practical advice derivedfrom their many years of experience.

The schedule for July and August isprinted on this page. In addition, watchfor posters at your local aviationorganisation for a seminar near you.

Thursday 10 July, 7.00 pm – 10.00 pm.

Heli-Kiwi Seminar. Presented byRay Wilson. Ardmore Aerodrome, atAuckland Aero Club.

Saturday 12 July, 9.30 am - 12.30 pm

Heli-Kiwi Seminar. Presented byBernie Lewis. Whangarei Aerodrome,at Northland Districts Aero Club.

Saturday 12 July, 9.30 am – 12.30 pm

Heli-Kiwi Seminar. Presented byIan Wakeling. Masterton Aerodrome,at Heli-flight Wairarapa.

Sunday 13 July, 9.30 am – 12.30 pm

Heli-Kiwi Seminar. Presented byRay Wilson. Whakatane, at WhakataneDistrict Council building.

Tuesday 15 July, 7.00 pm – 10.00 pm

Heli-Kiwi Seminar. Presented byBernie Lewis. Taupo Aerodrome, atTaupo Aero Club.

Wednesday 16 July, 7.00 pm – 10.00 pm

Heli-Kiwi Seminar. Presented byIan Wakeling. Nelson Airport, at AirNelson Training and AdministrationCentre.

Thursday 17 July, 7.00 pm – 10.00 pm

Heli-Kiwi Seminar. Presented byRay Wilson. Taieri Aerodrome, atOtago Aero Club.

Sunday 20 July, 9.30 am – 12.30 pm

Heli-Kiwi Seminar. Presented byBernie Lewis. Hastings Aerodrome, atHawkes Bay and East Coast Aero Club.

We urge you to attend

whichever type of seminar

is close to or most

convenient for you.

* It is permissible to fly into Ohakea if aircraft type, registration, ETAand advice that you are attending the Heli-Kiwi seminar are notifiedto Base Operations (Ph 0–6–351 5442, Fax 0–6–351 5448) by middayFriday 25 July. If driving in, visitor passes and directions will be availableat the Ohakea main gate. A visit to ATC will be possible immediatelyfollowing the seminar. The Museum cafeteria will be open for lunch.

Safety SeminarsSunday 20 July, 9.30 am – 12.30 pm

Heli-Kiwi Seminar. Presented byNeil Scott. Wanaka Aerodrome, at theFlightdeck Café.

Monday 21 July, 7.00 pm – 10.00 pm

Heli-Kiwi Seminar. Presented byNeil Scott. Franz Josef, at Franz JosefGlacier Hotel.

Saturday 26 July, 9.30 am – 12.30 pm

Heli-Kiwi Seminar. Presented byIan Wakeling. RNZAF Base Ohakea,at Theatrette. Details below*.

Wednesday 6 August, 7.00 pm – 10.00 pm

Heli-Kiwi Seminar. Presented byNeil Scott. Christchurch Airport, atCanterbury Aero Club.

Thursday 7 August, 7.00 pm – 10.00 pm

Aero-Kiwi Seminar. Presented byRussell Baker. Twizel, at MackenzieCountry Inn.

Sunday 10 August, 9.30 am - 12.30 pm

Aero-Kiwi Seminar. Presented byRussell Baker. Invercargill Airport, atSouthland Aero Club.

Monday 11 August, 7.00 pm - 10.00 pm

Aero-Kiwi Seminar. Presented byRussell Baker. Queenstown, atSherwood Manor Hotel.

Sunday 17 August, 9.30 am - 12.30 pm

Aero-Kiwi Seminar. Presented byRussell Baker. Greymouth Aerodrome,at Greymouth Aero Club.

Aero-Kiwi and Heli-Kiwi – makingcommon sense common practice.

From September to November there will beAero-Kiwi Seminars at North Shore, Hamilton,Rotorua, New Plymouth, Gisborne, Pine Park,Wellington, Blenheim and Ashburton.


Grant Brophy is an expatriate Kiwi living in Daytona beach, Floridaand working as an Air Safety Investigator, specialising in air transportoperations and aircraft emergency response. He is a member of theInternational Society of Air Safety Investigators, the American Instituteof Aeronautics and Astronautics, and the Human Factors Society. Hehas recently taken up the appointment of Director of Safety for a newAmerican airline.

Although written from an American perspective, his story hasinternational relevance. We have, however, added two items which providea New Zealand focus. The diagrams were created by Vector, basedmainly on those in New Zealand AIC-GEN A92/86. They makeno pretence to scale.

A recent US National Transportation Safety Board (NTSB)study shows that 51 wake turbulence accidents and incidentswere reported in the United States between 1983 and 1993.

These events caused 27 fatalities and 8 injuries, and 40 aircraftwere substantially damaged or destroyed.

“The strongest vortices are producedby ‘heavy’ aircraft, flying slowly,

in a clean configuration.”

Two of those incidents involved airliners as the trailing aircraft– a DC9 in 1984 and an ATR42 in 1991. The leading aircraftin 31 of the occurrences were jet and turboprop airliners. Onlysix of the events involved a ‘heavy’ transport category aircraftin the lead.

Some may consider this a small plane driver’s dilemma. Notexactly ...

Viewed from behind the generating aircraft, the left vortex rotates clockwise andthe right vortex rotates counter-clockwise. They spread laterally away from theaircraft and descend 500 to 900 feet at distances of up to five miles behind it.Vortices tend to descend 300 to 500 feet per minute in the first 30 seconds.

By Grant M.Brophy

Vort

ices

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ead

late

rally

fro

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e re

ar o

f th

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rcra

ft

Up to 5 miles

500

-900

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Mcontinue to occur, causing deaths, injuries, and aircraft losses.In any event, wake turbulence is still out there, and we need tokeep in mind how severe wake turbulence can be. The followingcaptain’s report typifies the types of upsets being experienced:

“On a visual approach to MSP (flying a BA3100 Jetstream), wewere being vectored off the localiser at 4000 feet for spacing ontraffic ahead.

“While on a 30-degree heading and level at 4000 feet, weencountered the wake of a B757 ahead.

“Our aircraft rolled violently to the left (approximately 120-degree bank) and entered a rapid descent. The aircraft wascompletely out of control for several seconds.

“We regained control at approximately 2500 feet amsl (1700feet agl) and advised ATC of our encounter.

“We climbed and took a few minutes to clean up the cockpit.In the violent nature of this upset, various objects became flyingobjects. My flight bag (between the seats) flew up, tipped upsidedown, and landed on the floor. A metal ‘can’ for maintenanceforms hit me in the head, as did a file folder used for the deferrallog documentation.

“In the cabin, the wing spar cover came off and hit the rearbulkhead.

“Fortunately, no injuries were sustained by either crew orpassengers.

“At the time of our visual approach clearance, we were only3.5 miles behind the B757 and were 1000 feet below anddownwind of the B757’s flight path. We were vectored below,downwind, and behind the B-757.

“At the time of encounter, we were almost exactly two minutes(four miles) behind the B757, 1000 feet below his flight path atthe same position relative to the runway.

“Our aircraft rolled violently left, so we must have entered hisright wingtip vortex.”

any pilots are taught to be aware of wake turbulence.However, incidents and accidents due to wake turbulence


The NTSB study also documented three accidents and twoincidents involving medium sized aircraft trailing B757s as theleading aircraft in the period between December 1992 andDecember 1993.

A Cessna Citation, a Westwind, and a Cessna 182 crashed. Thepilots of an MD88 and a B737 experienced significant butrecoverable loss of control and were able to land safely and filereports.

Four of the aircraft descended below the glide path of theleading B757s. The other aircraft entered the vortex at about75 feet in ground effect. Two of the events happened while thetrailing aircraft were attempting to land on a parallel orconverging runway less than 2500 feet from the lead aircraft’srunway.

The training kit consists of a comprehensive, well-illustratedmanual titled: “Wake Turbulence Training Aid” in printed andCD-ROM formats, and an accompanying videotape.

The FAA plans to distribute the materials to military, generalaviation, and some participating foreign operators.

The programme is designed to educate pilots and air trafficcontrollers in how to avoid the wake turbulence phenomenonand increase situational awareness, especially when operatingVMC.

This article was prepared as a reminder to pilots, to make themaware of wake turbulence and how best to avoid it.

What is Wake Turbulence?All aircraft produce wake turbulence. Wake vortices are formedany time an aerofoil is producing lift. Lift is generated by thecreation of a pressure differential over the wing surfaces. Thelowest pressure occurs over the upper surface and the highestpressure under the wing. This pressure differential triggers theroll-up of the airflow aft of the wing, resulting in swirling airmasses trailing downstream of the wing tips. Viewed frombehind the generating aircraft, the left vortex rotates clockwiseand the right vortex rotates counter-clockwise. They spreadlaterally away from the aircraft and descend 500 to 900 feet atdistances of up to five miles behind it. Vortices tend to descend300 to 500 feet per minute in the first 30 seconds.

Light crosswinds may cause vortices to drift, and crosswinds inexcess of 5 knots tend to cause them to break up behind theaircraft. Atmospheric turbulence and several other conditionsgenerally cause them to break up more rapidly.

The intensity or strength of the vortex is primarily a functionof aircraft weight, wingspan, and configuration (flap setting,etc). The strongest vortices are produced by ‘heavy’ aircraft,flying slowly, in a clean configuration. For example, a ‘large’ or

Crossing departure courses

After takeoff, avoid subsequent headings which cross below and behind the pathof a larger aircraft.

Departure

“Light crosswinds maycause vortices to drift …”

Recommendations from the NTSB included providing trainingfor pilots that specifically related to the movement and avoidanceof wake vortices and techniques to determine relative flightpaths and separation distances.

The NTSB also recommended that air traffic controllers receiveannual refresher training regarding wake turbulence separationand advisory criteria.

Recently, a co-operative effort involving the FAA, the BoeingCompany, and a joint industry group developed trainingmaterials to meet that need.

“Helicopters also producewake turbulence.”

‘heavy’ aircraft that must reduce its speed to 250 knots below10,000 feet, and is flying in a clean configuration whiledescending, produces very strong wake.

Helicopters also produce wake turbulence. Helicopter wakesmay be of significantly greater strength than those from fixed-wing aircraft of the same weight.

Taking off behind a larger aircraft

Start takeoff from a point where your aircraft can be safely rotated before therotation point of the preceding larger aircraft, and establish a climb above itsfligh path until such time as a turn can safely be made clear of its wake. If this isnot possible, delay your takeoff.

Light Medium Heavy

Rotationpoint

If planning to take off from an intermediate point on the runway, when thepreceding aircraft has used full length, delay your takeoff. (Alternatively, usingfull runway length may enable you to remain clear of the wake.)


The strongest wake can occur when the helicopter is operatingat lower speeds (20 to 50 knots). Some mid-size or executiveclass helicopters produce wake as strong as that of heavierhelicopters. This occurs because two-blade main rotor systems,typical of light helicopters, produce stronger wake turbulencethan rotor systems with a greater number of blades.

Stay Heads-Up for Wake During theTakeoff and Landing PhasesWhile there have been rare instances where wake turbulencecaused structural damage, the greatest hazard is induced rolland yaw. This is especially dangerous during takeoff and landingwhen there is little height for recovery.

En route

Avoid flight below and behind a larger aircraft’s flight path. If a larger aircraft isobserved less than 1000 feet above you on the same track (same or oppositedirection) adjust your position laterally, preferably upwind.

Wake turbulence-induced roll rates can be extreme. Counteringroll rates may be difficult or impossible, even in highperformance aircraft with excellent roll control authority.

In fixed-wing aircraft, wake vortices begin as the nose is rotatedfor takeoff and continue throughout flight until the nosewheeltouches down on the runway once again. The vortices cancause problems for crossing or lower airborne traffic ondeparture. Low approaches, touch-and-goes, and go-aroundscan also cause problems for taxiing or departing aircraft.

During takeoff and landing, the vortices sink toward the groundand move laterally away from the runway when the wind iscalm. A crosswind of 3 to 5 knots will tend to keep the upwindvortex in the runway area and may cause the downwind vortex

“The onset of wake turbulence can beinsidious and even surprisingly gentle.”

to drift toward another runway. We also know that wake vorticessometimes bounce, diverge, and dissipate more rapidly in groundeffect.

The term ‘heavy’ serves as a clue to ATC to keep all trailingaircraft the following distances behind a ‘heavy’:

• other ‘heavy’ (more than 300,000 lb), at least 4 miles,

• ‘large’ (12,500–300,000 lb), 5 miles, and

• ‘small’ (under 12,500 lb), 6 miles.

In the United States, when a ‘heavy’ aircraft is not in the lead,standard separation is 3 miles between all aircraft, and as little

as 2.5 miles in some high-density traffic situations. From 1 July1994, the FAA implemented a measure that requires 4 milesseparation for all “small, large, and heavy” aircraft following aB757.

Touchdownpoints

Less

th

an76

0m

Wind

(2) parallel runway or vector

Note wind for possible vortex drift to the landing vector if practicable. Stay at orabove the larger aircraft’s final approach flight path. Note its touchdown pointand land beyond a point abeam it.

Touchdownpoints

(3) crossing runway

Cross above the larger aircraft’s flight path.

Touchdownpoint

Landing behind a larger aircraft:(1) same runway

Stay at or above the larger aircraft’s final approach flight path. Note itstouchdown and land beyond it.


New Zealand pilots should refer to the NZAIP fordetails of required separation standards.

Tower controllers typically provide wake turbulence separationfor departing aircraft by applying time intervals. The mostcommon of these intervals is 2 minutes for all aircraft behind a‘heavy’ on the same or parallel runway within 2,500 feet.

A similar restriction applies if the departing/trailing aircraftwill fly through the airborne lead aeroplane’s path. Controllersare supposed to impose a 3 minute delay for all aircraft makingan intersection or opposite direction takeoff behind a ‘heavy’.

Tower controllers are responsible for runway separation for allaircraft arriving or departing airports. Tower controllers do notprovide visual wake turbulence separation to arriving aircraft;that is the pilot’s responsibility. Only under IMC, or whenpilots are unable to fly visually, are controllers responsible forapplying the wake turbulence longitudinal separation distances.

Issues Impacting Visual SeparationAir traffic controllers may separate departing aircraft by visualmeans after considering aircraft performance, wake turbulence,closure rate, routes of flight, and known weather conditions.Controller visual separation of aircraft should not be appliedbetween successive departures when departure routes and/oraircraft performance would not allow the pilots to maintainadequate separation.

In the terminal area, the air traffic controller must have bothaircraft in sight and must be in radio contact with at least oneof them. The flight crew of the trailing aircraft must see thelead aircraft and be informed of the lead aircraft’s position, itsdirection of flight, and its crew’s intentions. The pilots of thetrailing aircraft must acknowledge sighting the lead aircraft andbe instructed to maintain visual separation. The tower controllershall not provide visual separation between aircraft when waketurbulence separation is required.

The onset of wake turbulence can be insidious and evensurprisingly gentle. There have been serious accidents wherepilots have attempted to salvage a landing after encounteringmoderate wake only to encounter severe wake turbulence. Pilotsshould not depend on any aerodynamic warning, but if theonset of wake turbulence is occurring, immediate evasive actionis a must!

“Wake turbulence-induced rollrates can be extreme.”

In controlled airspace with ATC radar coverage, the controllermust inform the pilot of converging traffic and about VFRtraffic.

In cruise, when IFR and VFR aircraft are sometimes separatedby as little as 500 feet, pilots must use proper avoidanceprocedures. Because wake turbulence is nearly always invisible,pilots need to anticipate where it might be, based on experienceand through knowledge of current wind conditions. Air trafficcontrollers issue “Caution – wake turbulence” warnings onlyand are not responsible for anticipating the existence or effectof the condition.

The Warning SignsAny uncommanded aircraft movements such as wing rocking,may be caused by wake vortices. This is why maintainingsituational awareness is so critical. Atmospheric turbulence isnot unusual, particularly in the approach phase. Pilots whosuspect wake turbulence is affecting their aircraft shouldimmediately get away from the wake, execute a missed approach,or go-around, and be prepared for an even stronger wake vortexencounter.

Touchdownpoint

Rotationpoint

Landing behind a departing larger aircraft:(1) same runway

Note larger aircraft’s rotation point, and land well before it.

Touchdownpoint

Rotationpoint

Rotationpoint

(2) crossing runway

Note larger aircraft’s rotation point. If the point is past the intersection, continuethe approach and land preferably before the intersection.

If the larger aircraft rotates before the intersection, avoid flight below its flightpath, Abandon the approach unless a landing is assured well before reaching theintersetion.

(3) crossing runway


How to Avoid Wake TurbulencePilots should remember three basic warnings concerningwake turbulence.

• Do not get too close to the lead aircraft.

• Do not get below the lead aircraft’s flight path.

• Be particularly wary when light wind conditions exist.

The following avoidance procedures should be followed atall times:

Takeoff. If you think wake turbulence from the precedingaircraft may be a factor, wait between 2 and 3 minutesbefore taking off. Before taking the active runway, tell thetower that you want to wait. Plan to lift off prior to therotation point of the lead aircraft, and use full takeoffpower/thrust.

Climb. If possible, climb above the lead aircraft’s flight path.If you can’t out-climb it, deviate slightly upwind, and climbparallel to the lead aircraft’s course. Avoid headings thatcause you to cross behind and below the aircraft in frontof you.

Crossing. If you must cross behind the lead aircraft, try tocross above its flight path or, terrain permitting, at least1,000 feet below .

Trailing. Endeavour to stay either on or above the leadingaircraft’s flight path, upwind, or terrain permitting, at least1,000 feet below.

Approach. Maintain a position on or above the lead aircraft’sflight path with adequate lateral separation.

Landing. Ensure that your touchdown point is beyond thelead aircraft’s touchdown point. Land well before a

departing aircraft’s rotation point.

Crossing Approaches. When landing behind anotheraircraft on crossing approaches, cross above the otheraircraft’s flight path.

Crosswinds. Remember crosswinds may affect the positionof wake vortices. Adjust takeoff and landing pointsaccordingly.

Helicopters. Remember that their wake vortices may beof significantly greater strength than fixed-wing aircraftof the same weight. Avoid flying beneath the flight pathsof helicopters. When piloting a small aircraft, avoid taxiingwithin three rotor blade diameters of a helicopter that ishovering or hover taxiing at slow speed.

Visual Approach. When making a visual approach, do notassume the aircraft you are following is on the same orlower flight path. The flight crew of the lead aeroplanemay have flown a steep approach (typical of cargooperations). Stay above and at least 3 miles behind thenormal flight path; remember at least 4 miles behind aB757.

Wake turbulence is one of the factors that pilots and airtraffic controllers must avoid to ensure safe flights. It takesco-operation, awareness, and the understanding of eachother’s requirements to safely avoid aircraft generated wake.

It is your responsibility as flight crew or pilot in commandto anticipate the likelihood of encountering wake turbulenceand to alter your flight path accordingly, or if necessary, requestan alternative clearance from ATC. Don’t always rely onothers to provide warnings. Safe flying!

The article above by Grant Brophy is written mainly from an Americanperspective. The following translates the lessons into the New Zealandcontext (based on NZAIP Planning Manual, RAC9) – but rememberthat both countries experience the same laws of physics!

Wake turbulence separation is provided by ATC to all aircraftwhich may be affected by wake turbulence, except in thecase of VFR arrivals, or IFR aircraft making a visualapproach. In these cases it is the pilot’s responsibility to provideadequate spacing from preceding arriving or departing aircraft.Pilots should follow the guide-lines below and ATC will makeallowance when sequencing.

Wherever practicable, aerodrome controllers will advise pilotsof the likelihood of wake turbulence by the phrase: “Caution –wake turbulence”.

Weight CategoriesFor the purpose of assessing wake turbulence separation, aircraftare divided into the following weight categories:

Heavy (H)

All aircraft types of 136,000 kg maximum weight or more(includes A330, A340, C5A, C141, B777, B767, B747, B707,DC8, MD11, KC/DC10)

Medium (M)

Aircraft types of less than 136,000 kg but more than 7,000kg maximum weight (includes B757, B737, B727, FK27,

Wake Turbulence Separation in New ZealandFK28, DHC8, ATR72, BAe146, C130, DC3, Jet Falcon (allmodels), P3, Saab 340).

Note: B757 aircraft will be categorised as ‘heavy’ (H) aircraftfor the purpose of assessing wake turbulence to followingaircraft.

Light (L)

Aircraft types of 7,000 kg maximum weight or less (includesCessna 402, Cessna 421, Islander BN2, Nomad, PA31, Be99,Bandeirante E110, Metroliner).

Wake turbulence separation standards do not apply whena ‘light’ aircraft will cross the track of, or follow thetrack of a ‘medium’ aircraft of less than 25,000 kgMCTOW.

This is a recent change, and the ‘medium’ type aircraft involvedinclude the ATR72 and DHC8. Pilots can still requestseparation by advising the Tower prior to entering the runwayfor takeoff.

Wake Turbulence SeparationThe New Zealand situation is similar to the US for separationof aircraft following or crossing behind a ‘heavy’ aircraft duringthe approach and departure phases of flight, when the aircraftis under radar control. If the following aircraft is a ‘heavy’,separation is 4 miles, if a ‘medium’, 5 miles and if a ‘light’, 6miles.


Many pilots have received a fr ight from unexpectedlyencountering wake turbulence. Fortunately, in New Zealandaccidents resulting from wake turbulence have been rare.

A recent example, however, occurred after a pilot at WellingtonAirport exercised the option of requesting exemption from waketurbulence separation standards. The Cessna 185 aircraft wasdeparting behind a Boeing 727, and the pilot elected to maintainown wake turbulence separation. After getting airborne theCessna flipped in a right turn and crashed on the westernboundary of the airfield.

Other incidents recorded on the CAA database include:

• In 1993 a Fairchild SA227-AC on approach at Christchurchairport encountered strong wake turbulence at about 50 feetagl and made a go-around.

• In 1994 a Saab SF340A on approach to Auckland behind aBoeing 747 encountered wake turbulence requiring extremecontrol input and power application. A go-around was made.

• In 1994 at Christchurch a Boeing 767 had departed full lengthfrom runway 20. A Cherokee PA28-140 then departed fromgrass 20. The Cherokee encountered severe wake turbulenceresulting in a 60 degree wing-down upset.

• In 1996 during an approach to Auckland a PA31-350experienced a short burst of wake turbulence from a precedingBoeing 747 while over Westpoint. The pilot reported thatthe 747 was descending through their level, and the PA31pilot was trying to position on its upwind side beforecommencing the ILS for Runway 05 visually into Auckland.

Other incidents recalled by pilots include:

• A Piper Cub departing the circuit to the west fromChristchurch passed under the flight path of a Boeing 747joining downwind. Although some distance behind and belowthe 747, a sudden 80 to 90 degree upset was experienced.

• The most severe wake turbulence experienced by one lightaircraft pilot was from aircraft of a similar type – on takeoffclose behind – showing that light aircraft can also generatesignificant wake turbulence for another light aircraft.

An air traffic controller recalls the following incidents atWellington in past years and makes a pertinent observationregarding Wellington. On windy days in Wellington, the challengeis in battling the windshear, gusts and crosswinds; wake turbulenceis not a great danger because in these conditions it is rapidlydispersed. On the other hand, there is a danger that pilots relaxwhen flying on a fine calm day at Wellington – when they shouldbe alert to the hidden hazard of wake turbulence!

• A light aircraft was downwind at Wellington and acceptedthe controller’s request that an overtaking Boeing 737 couldpass overhead and then descend in front of the light aircraft.The 737 was slow, clean and then levelling out (all factorswhich produce the strongest wake turbulence). The lightaircraft experienced a 270 degree roll, with the startled pilotelecting to continue the roll to reach level flight again.

• A Cherokee Six on approach behind a Boeing 737experienced a 90 degree roll to the right. The flight path wasthe same profile as the Boeing. The pilot describes theexperience as if someone had grabbed the propeller andstopped it but the aircraft continued rotating. It was then spatout the side like a surfer on a big wave getting flipped off thesurfboard.

• A Cherokee 181 made a reduced length takeoff behind aBoeing 737 which had used full length on Runway 16. Justafter takeoff the Cherokee experienced a severe upsetsufficient to alter heading to the left towards buildings andparked aircraft. The pilot regained control while over themain taxiway and was then able to return to the originalrunway heading.

Be warned. It can happen to you.

Wake Turbulence Encounters in New Zealand

If the leading aircraft is a ‘medium’, then separation for afollowing ‘heavy’ or ‘medium’ is 3 miles, and for a ‘light’, 5miles (the latter only if the ‘medium’ is above 25,000 kg).

When the leading aircraft is a ‘light’, then separation is 3 milesfor all following aircraft.

As noted above the B757 is categorised as ‘heavy’ in relation tofollowing aircraft.

Non-radar separation standards for arriving or departing flightsfor aircraft using the same (or close parallel) runway are between2 to 3 minutes, as follow:

• Separation between arriving flights following a ‘heavy’ is 2minutes for a ‘medium’ and 3 minutes for a ‘light’. A ‘light’behind a ‘medium’ is normally 3 minutes, but the recentchange means there is no time requirement behind a small‘medium’ such as ATR72 and DHC8.

• Separation between departing flights of all categories is twoto three minutes depending on the second aircraft’s takeoffposition (2 minutes from the same position, 3 minutes froman intermediate takeoff position).

• Separation between arriving and departing flights of allcategories is normally 2 minutes.

These are elaborated on, and there are further standards listedin the AIP, for example, for opposite direction runway operationand for crossing runways.

Remember wake turbulence separation is not providedto landing VFR arrivals, nor to IFR on visual approach.In these cases, it is up to the pilot to provide adequatespacing from preceding arriving or departing aircraft.

Pilot OptionsIf a pilot considers the wake turbulence separation standardsinadequate, an increased separation may be requested byspecifying the spacing required.

Conversely, if pilots indicate that the effect of wake turbulencecan be nullified by ensuring that flight profiles do not cross,they may request and be granted exemption from theseseparations. This option should be treated with caution.(See “Wake Turbulence Encounters”.)

Jet BlastAnother hazard to bear in mind when taxiing, particularly forlight aircraft, is jet blast and propeller slipstream. Beware ofpassing close behind aircraft with engines running, particularlylarge jets.

Jet blast and propeller slipstream can produce localised windvelocities of sufficient strength to cause damage to other aircraft,vehicles and personnel – and to buildings. A B727 on enginetests blew in a hangar door some years ago at a New Zealandairport – clear testimony to the force which can be produced.


What is a UNICOMService?As of 14 August, the Aerodrome FlightInformation Service (AFIS) will bewithdrawn from Taupo and a UniversalCommunications (UNICOM) servicewill be provided. The following looks atwhat a UNICOM service comprises andhow it operates. It is worth noting that aUNICOM service is currently operatingat Mount Cook.

UNICOM is a radio base provided bytrained operators. It provides someinformation to aircraft operating at anaerodrome, but it does not provide thesame service as an AFIS. Perhaps the bestway to describe the system is to compareit to an AFIS. See table below.

Taupo UNICOMEffective from the evening of 13 August1997, the Airways Corporation AFIS willbe withdrawn from Taupo. From themorning of 14 August, the Taupo DistrictCouncil will operate a UNICOMservice.

These changes are being made after along period of consultation betweenAirways Corporation, the Taupo DistrictCouncil, airport users, and the CivilAviation Authority. The CAA carried outa safety assessment at Taupo anddetermined that the provision of an AFISwas not required under the currentconditions. The CAA did, however,

require the Taupo District Council toconsider other safety initiatives. “TaupoUNICOM” has been developed to meetsome of the safety recommendationneeds.

In developing this UNICOM, it wasnecessary to consult widely with the usersand establish new operating proceduresfor when the AFIS closes.

The Taupo ServiceDuring operating hours, the TaupoUNICOM system will provide thefollowing services:

• Hourly MET Reports, METARS, andSPECI (and these will be availablenationally).

• An Aerodrome Terminal InformationService (ATIS) on 125.2 MHz,updated as required.

• A base radio service on 118.4 MHz,available during published hours,generally 7.00 am – 6.30 pm.

• A telephone service during publishedhours.

• Hotel, taxi, rental car bookings andpayment of landing charges.

More specific operational informationwill be circulated as the changeover timenears. In the meantime, if you have aquery, ring or write Roy Carmichael,Airport Manager, Taupo District Council,Private Bag Taupo. Ph 0–7–378 7771,Fax 0–7–378 7776.

New AirspaceProceduresThere will be changes to airspacemanagement in the Taupo area. Thesechanges are intended to make theairspace safe and user-fr iendly. Theprocedures are being developed with thefull cooperation of the Taupo AirspaceUsers Group, operators, CAA and theAirways Corporation. The changeoverdate has been deliberately set to coincidewith the reissue of the VFG amendments.

A Mandatory Broadcast Zone (MBZ)will be effective on 14 August. At first itwill be designated as a Restricted Areauntil the implementation of the newairspace Rules, when this will allow it tobe designated as a Mandatory BroadcastZone. Until this time the Restricted Areahas special conditions that are as follows:

You may enter and operate within theTaupo MBZ only if you:

• broadcast aircraft callsign, position,altitude and intentions on theappropriate frequency:

- at entry,

- every 10 minutes, and

- upon exit; and

• have the landing lights or anti-collision lights on if practicable.

You do not require the permission of thecontrolling authority, CAA, to enter theMBZ, as long as the conditions aboveare complied with.

For depiction of this area, see the TaupoVTC, effective 14 August 1997.

For more information, your attention isdirected towards the AIP Supplementdescribing the Taupo MBZ.

Note that the above MBZ explanation willapply also to Paraparaumu, also with effectfrom 14 August 1997 (see the WellingtonVTC). Whether Paraparaumu wouldhave a UNICOM was a decision notevident at the time we went to press.

Introducing Taupo UNICOM

Operates regular hours, basedaround the operation of theaerodrome.

Is not necessarily provided around thegeneral operational hours of anaerodrome. It depends on thepriorities of the provider.

Does not provide an alerting service.

Is not certificated.

May relay traffic position informationonly.

May provide meteorologicalinformation. It may provide an ATIS.

An AFIS ...

Provides meteorological information.

Provides traffic avoidance informationas well as aircraft position information.

Is certificated by the CAA under RulePart 172.

Provides an alerting service (includingSAR) to all aircraft.

A UNICOM service ...


The reporter (a flying instructor) and the pilotin command of this aircraft experienced whatevery pilot hopes will not happen to them.This account shows the importance of stayingcalm (relatively), remembering to Aviate,Navigate and Communicate, and keepingcurrent on forced landing procedures.

Contrary to popular belief I was notlooking for an excuse to go swimming –I had one of those experiences that provesthe old joke to be true. You know theone, “The only reason an aeroplane hasa propeller up the front is to keep thepilot cool, because you watch them sweatwhen it stops going around.”

trip with diversions around weather andan early stop required in Hamilton toget gas and relieve my Woolworth’sbladder. After topping up in Hamiltonwe went through to the west coast justsouth of Raglan and took a straight linedown the coast and through ‘tigercountry’ to Hawera. Some localised cloudbetween Hawera and Wanganui took usdown to 700 feet, but that cleared andwe were back at 1500 feet for the rest ofthe tr ip down the west coast, pastParaparaumu and then on the home runinto Wellington.

After we had called Wellington Tower andbeen identified and cleared to enter theControl Zone, we headed towardsAvalon. Just as we were crossing theeastern side of the Pauatahanui Inlet,however, the engine stopped – nowarning, no coughing, no spluttering –just silence. We began some immediateactions and it roared back into life atabout 80 percent power. Dave (pilotflying) advised the Tower that we weregoing back to Paraparaumu due to lowfuel; it was the first thing that came tomind. After the call, and after we hadstarted a lefthand turn back towardsParaparaumu, the engine stopped again.This time it stopped totally – which iswhen all the action started.

Dave called a Mayday and completedsome checks but was mostlyconcentrating on where we were goingto land. Because this aeroplane was notbuilt to glide well and has a considerablelanding distance, there were no paddocksbig or near enough in which to land. Ouronly other option was into the inlet.Luckily, because we regularly fly aroundWellington, landing in the water hasalways been a likely option to beconsidered. But we had to make it to thewater, and this was not as easy as it wouldseem, as we were now over the hills tothe northwest of the inlet.

All hell was breaking loose inside thecockpit as Dave tried to restart the enginetwice, fly the aeroplane, choose a landingsite, as well as having the controller askfor another position report. Dave and Iworked together confirming each other’sdecisions – proving that two heads canbe better than one.

The sensation was one of plummetingas opposed to gliding, and we had to pickour way down to the water very carefully.The landing had to be downwind so thatwe could land in the clear shallow waterand not on the nearby rocks. We werelosing height very quickly and I estimatethat we were doing about 1000 feet perminute down and maintaining 80 knots,

“I’ve survived this crash,and now I’m going to

drown ...”

It Can Happen!

I wouldn’t say that I sweated, but the stresslevel went through the canopy.

I was a first-time passenger in ahomebuilt Lancair aeroplane, which is atwo-place fibreglass, high-speedaeroplane with short stubby wingsdesigned for speed – not for gliding.

We were coming home from theRNZAC national competitions inWhangarei, and it had been an interesting

A fire officer inspects the wreckage of the Lancair as it rests partially submerged in the Pauatahanui Inlet, near Wellington. Photograph by Mark Round, Dominion.


so as not to stall. Needless to say we weremoving very quickly when we hit thewater.

As we struck we were in a tail-low andleft-wing-low attitude, and the first thingto give was the tail which broke off. Thenthe left wing struck the water and ripped,but it remained connected. This spun usaround so that we were facing in theopposite direction. The cabin stayedintact and I was pretty much unharmedapart from a few cuts and bruises and aknock on the scone.

Answers to questions.

• Yes, I thought I was going to die. Ithought this twice, once when theengine stopped the second time, butonly for a millisecond, and then againjust before we hit the water.

• No, my life did not flash before myeyes. Some say this was because I haveyet to have one!

• No, time did not slow down. I havehad time slow down on a number ofoccasions before and this time itdefinitely seemed to go very quickly.In fact we had about a minute and ahalf before we hit the water and itwent very quickly.

• Yes, I am flying again and enjoying it,although it took me a while to beconfident again.

• No, I do not want to do anything likethat again, and when I am teachingstudents about forced landingswithout power I will never again saythat catastrophic engine failure is veryrare and unlikely to happen.

What actually saved my life?

• A full harness with both shoulderstraps firmly attached.

• A fibreglass aeroplane that was strongaround the passenger compartmentand yet able to break at the extremitiesto absorb some of the impact.

• A level head.

• Having someone know where wewere so that they could sendambulances, etc, to a precise location.An accurate Mayday call, and a filedflight plan.

• Being aware of the priorities duringa forced landing, and being fairly wellpractised. I wouldn’t consider that Iwas particularly good at forcedlandings, but I was familiar with thembecause I teach them to others.

• Dave and I worked very well togetheras a team, he flew the aeroplane and Italked to him, reassuring him thatwhat he was doing was right andconfirming our decisions.

I am not sure whether this will make mea better pilot, but I consider myself veryvery lucky, not only to walk out of anaircraft wreck like that, but also that theengine didn’t spit its dummy somewherea lot more uninviting.

The complete Lancair prior to departure on the day of the accident.

“Being aware of thepriorities during a forcedlanding, and being fairly

well practised.”

I must have blacked out because I don’tremember the crash; all I can rememberis what it looked like just before we hitthe water, water coming in the canopyat me and then waking up sitting in theaeroplane facing in the other direction,up to my waist in water.

When I came around I immediatelythought “I’ve survived this crash, and nowI’m going to drown”, so I grabbed at myseatbelt to undo it, but soon realised thatI wasn’t getting any lower in the water.First panic over.

Dave and I checked that each other wasokay, and we debated who was going toswim to shore. I told him there was noway he was leaving me there, we weregoing together. When Dave jumped out,however, the water was only waist deep,so we waded out.

On the shore were a number of peoplejust sitting looking at us and we musthave looked a sight. Two drenched people,clinging to each other and holding ontobleeding heads. Unfortunately at thispoint I lost my cool, because none ofthem even tried to help us out of thewater, and I swore at them (as I tend todo) to go and get blankets or towels.

The ambulances were pretty quick toarrive, and as soon as they did I couldstart relaxing and leaving the aftermathfor someone else to deal with. Up untilthat point I was concentrating on keepingDave awake and trying to slow anychances of hypothermia setting in.

It Can Happen!

The Civil Aviation Authorityinvestigation into this accidentrevealed the probable cause as ajammed valve spring within theengine.

The investigation showed there wasnothing wrong with the fuelsupply.

The only item found defectiveduring a complete strip of theengine was a broken inlet valveouter spring which had becomejammed with the inner spring.

The positioning of the valve couldnot be conclusively determined,but if it had been jammed open itwould have resulted in completepower failure.

Photograph by Peter Lowe.


In recent times the safety of the PiperTomahawk has been questioned in a numberof publications, so people have started toquestion the airworthiness of this trainer. Wereceived a letter from Ken Wells, an ‘A’ CatInstructor from Nelson, asking us to confirmthat this popular aeroplane is still safe. TheCAA and Vector believe that, yes thisaeroplane is still safe, but, it does require skilland caution when flying it – as do many otheraircraft.

What the Article SaidThe original article that caused most ofthe concern in New Zealand wasreprinted in New Zealand Airline Pilotmagazine in June 1996. This article seemsto have originated from Aviation Safetymagazine, February 1995, and it workedits way around the world in a number ofmagazines.

It was a particularly damning report onthe aeroplane by the reporter and bysome ex-Piper employees. It made anumber of claims, some of which werepeat here.

“It may be that no Tomahawks stall the sameand that no Tomahawk stalls the same fromday to day”

“...it appears that the PA-38-112 prototypebuilt at Piper’s Vero Beach, Fla, facility wasnot the aircraft produced at the Lock Haven,Pa, facility ... major structural changes [were]made without consulting the design engineers... contrary to the FAA-approved conformityspecifications and the sealed drawing lists.[These changes were made] to reduceproduction costs.”

“new evidence indicates that the productiondesign team at Lock Haven changed many

The Trusty Tomahawkthings in an attempt to cut production costs... [including] lightening the wing structure.”

“This noticeably ‘softened’ the wing, makingit a new commodity in stalls and spins.”

“The production aircraft has an entirelydifferent wing spar arrangement.”

“The aluminium skin covering the airplanewas changed to a thinner gauge, apparentlywithout testing and FAA approval. Engineoffset angle was changed, too, without benefitof flight testing.”

“NTSB investigators have been unable todetermine who retested and approved this newaileron design.”

“The aileron controls are a booby trap. Theycan generate large undesirable yaw excursions.”

“Removal of the wing root glove was thegreatest mistake.”

“The Tomahawk wing under G loading tendsto ‘crease’ just outboard of the fuel tank, ratherthan bending smoothly upwards as the lift loadis increased.”

These claims are of concern to all of uswho fly or have flown Tomahawks, butthey are not all as accurate as they seem.It has been pointed out by onecommenter (James Allen, Pilot magazineJanuary 1997) that “In context oneshould perhaps remember that it is quiteeasy to find ex-employees of anycompany that has gone into liquidationwho feel rather bitter about things”, andanother commenter, Bruce Landsberg ofthe AOPA Air Safety Foundation agreesthat these claims have little substantiation.

A number of the claims made above havebeen repeated in other articles, butrepetition does not mean validation.

What the FAA SaidAs soon as the CAA became aware ofthe article, Geoff Connor, ContinuingAirworthiness Analyst (the man thatwrites the Airworthiness Directives)wrote to the FAA asking for furtherinformation on the airworthiness of theTomahawk, and asked if they intendedany action in response to the recentaccident investigations.

“It is important thatinstructors know and

teach the correct standardtechnique for recovery.”

The FAA were more than satisfied withthe certification and flight testscompleted on the type-certifiedaeroplane. A total of 85 certificationflights totalling 69.5 flight hours werecarried out. Of this, 11 hours was usedto determine the stall characteristics and11.75 hours to conduct a total of 99 spins.This included a ser ies of 18 spinsconducted by an FAA pilot.

Conforming drawings for thecertification aeroplanes show that thewing assemblies and aileron assembliesare the same as shown in the currentIllustrated Parts Catalogue. The FAA goeson to say that they conducted static testson the wing assemblies and concludedthat the wing is not “soft and flexible”.

The FAA confirmed that there was anexperimental prototype, but it was nevercertificated and it was significantlydifferent from the production aircraft.


Furthermore, a meeting was held at thePiper facility in August 1995, whererepresentatives of Piper engineering, theNTSB (National Transportation SafetyBoard) and the Atlanta AircraftCertification Office of the FAA were inattendance. Video tapes of spin tests onthe Tomahawk were reviewed, and theparticipants concluded that the aeroplanebehaved as expected and did not exhibitwing flexing nor poor aileron response.The FAA, NTSB and Piper agree thatthere is no need for change in theaerodynamic design.

CAA CommentThe CAA is satisfied with the responsefrom the FAA, especially as theNTSB are in concurrence with therecommendations. As for the accidentrate in New Zealand, there are no knowncases of stall-spin accidents in NewZealand, and it seems that there are veryfew cases in the UK.

CAA does point out, however, thatAirworthiness Directive DCA/PA38/19requires installation of additional flowstrips within the next 100 hours time-in-service as from 19 August 1983, tostandardise and improve the stallcharacteristics. This should mean thatthere are no Tomahawks in service inNew Zealand without inboard andoutboard flow strips (unless of course theTomahawk has not done 100 hours since1983).

Views ofExperienced PeopleVector canvassed a number of experiencedNew Zealand operators and pilots aboutthe Tomahawk.

Graham LeachFlight Examiner – ASLI have been instructing and/or testing inTomahawks since they first arrived inNew Zealand in the late 1970s.In fact, at Masterton we were one of thefirst clubs to purchase two aeroplanes, thefirst, ZK-WRC with outboard flow stripsonly, and ZK-WRB withboth inboardand outboard strips. In my opinion,both displayed quite positive stallcharacteristics, with the outboard flowstrips making for classic wing drop at thestall, while with the inboard strips as well,this effect was reduced. I was always ofthe opinion that the original aeroplanedisplayed all the desirable stall

characteristics of a good basic trainer (ie,stall leads to a wing drop and, if nocorrective action is taken, possibly a spin).This behaviour is consistent with two ofthe most successful training aeroplanesof the past, the Harvard and the TigerMoth.

As far as the spin is concerned, I can onlyspeak from personal experience of manyspins, both as pilot in command and asan examiner. I can honestly say that I havehad no problems with recoveryprovided the correct standardrecovery technique is employed.

It is important that instructors know andteach the correct standard technique

Warren SattlerCFI – Ardmore Flying SchoolThe recent article on the Tomahawkwhich found its way into var iouspublications is certainly one of the mostbiased articles I have ever read. Myfavourite Tomahawk, ZK-EVB, has justpassed the 14,000 hour mark, whichincludes around 6,000 hours completedby myself. If the article is a true statementof the Tomahawk, then I am certainlylucky to be alive.

My first real experience with Tomahawksstarted in the late 1980s. I must admitthat initially I wasn’t all that impressed –it was different from what I was used to.After a short time though, I really startedto appreciate the difference.

The Tomahawk was designed witha cockpit four inches wider than itsdirect competitor, the Cessna 152. To compensate for the increased dragcaused by the increased frontal area, thedesigner selected the GAW 1 wingsection (a maximum critical wing section

“We must … not assumethat one light trainer is

like another.”

“All aircraft have differenttraits, and the Tomahawk

is no exception.”

for recovery. I have spun the Tomahawkfrom level flight and from steep andgliding turns with predictable results,provided the correct procedure isfollowed.

In summary, I have had no problems withthe PA-38 and neither, to my knowledge,have my students. It is refreshing to see abasic trainer that behaves in a ‘classic’fashion in the stall/spin regime. Manymodern trainers have had thesecharacteristics designed out of them, andpilots tend to expect the Tomahawk tobe just as docile – which it is not.

If I have a criticism of the aeroplane, itwould be the lack of time between thestall onset and the nose/wing drop. Thisis not really a problem, but often it resultsin a slightly greater height loss than inother aeroplanes when recovering at theincipient stage.

developed by Richard Whitcombe ofNASA – the wing was found to have a14 percent increase in efficiency over thetotal speed range). This enabled thedesigner to reduce the wing area ofthe Tomahawk to 124.7 square feetcompared to 159.5 square feet for aCessna 152.

Turns and stalls are standard, with a wing-drop stall being a good deal more docilethan a 152. However if you try tospin the Tomahawk like a Cessna 152,watch out. Spin recovery in a 152is straightforward, but not so in aTomahawk. If you treat a Tomahawk likea 152 then the comments on spinning

in the article have merit. You needto check fully forward to commencethe recovery, the spin will tightenmomentarily and then the aircraft willexit the spin. Tiger Moth pilots will feelright at home with the Tomahawk’s spincharacteristics and recovery technique.The stall/flow strips on the wingscertainly make a difference – perhapsmaking the aircraft a little too docile.


I wonder how many pilots bother to readthe Flight Manual fully before flying aparticular aircraft. All too many pilotsbelieve that, because they can spin oneaircraft, then they can spin all aircraft. TheTomahawk Flight Manual is very specificwhen it comes to spinning [see excerptsreprinted from the Flight Manual –Ed].

Depending on the yearand model (and we’ve got 16 Tomahawkson line to compare) some will tin-can,some won’t – it seems Piper learnt a bitabout sound-proofing and noiseprevention as time went by.

I have total confidence in the structuralintegrity of the aircraft and have neverhad cause to doubt it. I am more thanhappy training in Tomahawks and willcontinue to do so, and hopefully for sometime to come.

Tips From ProfessionalsThe following is supplied by MurrayFowler, CAA Field Safety Adviser, andGraham Leach.

TurnsAccurate speed control, balance andcorrect technique using power enteringturns, in particular at low level, is a must.An out-of-balance and inadvertent stallcan produce a stall-spin situation withrapid height loss. The PA-38 can enterthis predicament very quickly for theunwary or careless.

StallingThe PA-38 can demonstrate abruptnessand unpredictability at the stall,particularly in the ‘clean’ configuration.If the aircraft is kept in balance, it is stillprone to drop a wing quite easily, and itwill go either way. The stall onset (buffet)is usually short and sharp followed by thewing drop, if it is going to occur in thisconfiguration.

If flap and a little power is employedentering the stall, the stall characteristics

are generally softened somewhat, and theaircraft is usually less prone to drop awing.

It is very important in the PA-38 (as inall types) not to enter the stall ‘crossed

up’, that is,

using too much rudderand having to use opposite aileron tokeep the wings level. In this situation theaircraft is prone to quietly drop the wingin one direction and then rapidly flickinto a spin in the opposite direction.

A fully developed stall can produce quitea steep nose-down attitude, but it isimportant to ensure that the elevatorcontrol is moved forward enough topositively unstall the aeroplane. Failureto do so may recover the aircraft justenough to put it back into the buffettand re-enter another stall immediatelywith further height loss. Because of this,normal stall entry and recoverytechniques should always be employed.

Ease forward, full power and toprudder to prevent yaw. If you mustlead with any control it would be theelevator, but the actions should be‘simultaneous’.

Using the normal recovery techniqueyou will have no trouble recovering aPA-38 from the stall.

SpinningThe PA-38 spins quite easily, as alreadymentioned. It is quite predictable in therecovery, once again using accepted‘normal’ technique.

This is:

1) Power off

2) Ailerons neutral

3) Full opposite rudder – pause*

4) Stick forward until spin stops

5) Centralise rudder

6) Level the wings and ease out of dive

7) Apply power as the nose rises throughthe horizon

“ … there are no known cases of [Tomahawk]stall-spin accidents in New Zealand …”

“… how many pilotsbother to read the Flight

Manual fully before flyinga particular aircraft.”

The “stick forward” part is important toany spin recovery. Some modern trainersrecover as soon as pro-spin control isremoved. This is not necessarily the casewith the PA-38.

The attitude during the autorotation isquite steeply nose-down, and

therefore self-discipline isrequired tobriskly move

the elevatorforward at the

appropriate time in the recovery.

The Flight Manual gives clear andconcise information on spinning entryand recovery techniques.

The C of G limits are very important,and it will be noted from the FlightManual that the forward and aft limitsare the same for the Utility and Normalcategories.

ConclusionThe Tomahawk is a classic case ofgetting what you asked for. When10,000 instructors were asked by Piperwhat they wanted, they wanted anaeroplane than spun well, and that iswhat they got.

All aircraft have different traits, and theTomahawk is no exception. We mustbe aware of these differences and notassume that one light trainer is likeanother.

* The pause in the normal recoverytechnique is to allow the rudder tobecome effective. In a conventionalconfiguration tailplane, if the elevators aremoved down too soon they could have ablanketing effect on the rudder, thusreducing the anti-spin yawing momentobtained from the rudder. Therecommended recovery technique in theTomahawk Flight Manual does notadvocate a pause, presumably because thisis not necessary with the T-tailconfiguration. In all other respects the spinrecovery technique is ‘normal’.

Tomahawk port wing leading edge, showing the inboard and outboard flow strips.


It is vitally important to study the aircraft flightmanual for any specific spinning characteristicsof any particular aircraft type. The PA-38Flight Manual section on spins is quitecomprehensive. A few pertinent points arequoted here.

Before Spinning“Carrying baggage during the spin isprohibited, and the pilot should makesure all loose items in the cockpit areremoved or securely stowed, includingthe second pilot’s seatbelt if the aircraftis flown solo.”

“Spins should only be started at altitudeshigh enough to recover fully by at least4000 feet agl, so as to provide an adequatemargin of safety. A one-turn spin,properly executed will require 1000 to1500 feet to complete, and a six-turn spinwill require 2500 to 3000 feet tocomplete.”

Spin Entry“The spin should be entered from apower-off glide by reducing speed atabout 1 kt/sec until the airplane stalls.”

Spin Recovery“Normal recoveries may take up to 1 to11/2 turns when proper technique is used;improper technique can increase theturns to recover and the resulting altitudeloss.”

“The recommended procedure has beendesigned to minimise turns and heightloss during recovery. If a modifiedrecovery is employed (during which apause of about 1 second – equivalent toabout one half turn of the spin – isintroduced between the rudder reachingthe stop and moving the control columnforward ) spin recovery will be achievedwith equal certainty. However, the timetaken for recovery will be delayed by thelength of the pause, with correspondingincrease in the height lost.

In all spin recoveries the control columnshould be moved forward br iskly,continuing to the forward stop if

necessary. This is vitally important,because the steep spin attitude mayinhibit pilots from moving the controlcolumn forward positively.

The immediate effect of applying normalrecovery controls may be an appreciablesteepening of the nose-down attitude andan increase in rate of spin rotation. Thischaracteristic indicates that the aircraft isrecovering from the spin, and it isessential to maintain full anti-spin rudderand to continue to move the controlwheel forward and maintain it fullyforward until the spin stops. The airplanewill recover from any point in a spin innot more than one and one halfadditional turns after normal applicationof controls.”

“Because the aircraft recovers from a spinin quite a steep nose-down attitude, speedbuilds up quickly in the dive out. Therudder should be centralised as soon asthe spin stops. Delay in centralising therudder may result in yaw and ‘fish-tailing’.If the rudder is not centralised it wouldbe possible to exceed the maximummanoeuvre speed (Va) of 103 kts withthe surface fully deflected.

Unintentional SpinsIn the “Emergency Procedures” section

of the Flight Manual, the spin recoveryadvice includes the important additionalpoints for an unintentional spin of closingthe throttle, retracting flaps if extended,and neutralising the ailerons.

Mishandled Recovery“The airplane will recover frommishandled spin entries or recoveriesprovided the recommended spinrecovery procedure is followed.”

“Delay of more than about 11/4 turnsbefore moving the control wheel forwardmay result in the aircraft suddenlyentering a very fast, steep spin modewhich could disorient a pilot. Recoverywill be achieved by briskly moving thecontrol wheel fully forward and holdingit there while maintaining full recoveryrudder.

If such a spin mode is encountered, theincreased rate of rotation may result inthe recovery taking more turns than usualafter the control column has been movedfully forward.

In certain cases the steep, fast spin modecan develop into a spiral dive in whichthe rapid rotation continues, butindicated airspeed increases slowly. It isimportant to recognise this condition.”

TomahawkFlight Manual Extracts


A Cessna owner-operator submitted thefollowing observations to the CAA.

Uncommanded SlidingSeatThe following report was taken from aclub newsletter, and it highlights an oftenneglected part of a preflight inspectionthat is worthy of consideration.

“The Cessna 172 pilot and his threepassengers were leaving for a one hourlocal scenic flight. At a height of 40 to50 feet the aircraft nose was seen to pitchviolently up and the power suddenlyreduced to idle. The aircraft subsequentlystalled heavily into the ground, with thepilot suffer ing a broken leg andpassengers suffering minor back injuries.”

aircraft, for applicable serial numberranges, requiring detailed inspection ofthe seat tracks to preclude the possibilityof lock pin disengagement. These arerepetitive inspections at 100 hourintervals.

Loose ShoulderHarnessThe second occurrence refers to theshoulder-harness to lap-belt connection.The submitter reports that theconnection became loose at theshoulder-harness to lap-belt attach studlocation. Investigation revealed that theplastic bushing on the shank of theshoulder harness lock stud (on the lapbelt) had broken and was missing,resulting in a totally unreliable shoulderharness. Replacement of the plasticbushing (part number S-2237-3) curedthe fault. Cessna Service Bulletins MEB96-4 and SEB 96-2 refer.

Cessna OwnersA Letter fromthe Field

upward force applied by the occupanton the shoulder harness. This can becaused through several reasons:

• The knurled clamping bar on the lapbelt that clamps the webbing is wornor rusty and loses its clamping effect.Where this condition exists, the beltshould be replaced.

• The webbing is worn or abraded, andthe knurled clamping bar can notprovide the required grip on thewebbing. Where this condition exists,the belt should be replaced.

• The seat belt buckle is positionedincorrectly, ie, in the centre of the lapof the occupant. The submittersuggests shortening the lap belt (thehalf with the buckle end) so that thelocking assembly is positioned moretowards the thigh of the occupant. Thisprovides for a greater angle across theoccupant and reduces the tendencyfor upward force to loosen the lap belt.

CAA CommentWhere the last option above is selectedas the only cure to the problem, operatorsshould ensure that there are nopromulgated modification restrictions onthe belt and that the belt modification isdone in accordance with approvedmodification data from the manufacturer,an approved design organisation, or theCAA. Reference material for webbingreplacement procedures is contained inFAA’s AC43.13-1A. Before attemptingany seat belt modification, theoperator should ensure that the seatbelt assembly is the correct partnumber for that installation.

The cause of the accident was the pilot’sseat moving rapidly fully aft. The pilot,with his hand on the throttle, was takenby surprise and pulled both the controlcolumn and the throttle aft with him.Unable to move the column or throttleforward the aircraft stalled. There wasinsufficient height to recover thesituation.

CAA CommentWhile it is important to ensure that seatsare correctly locked in place, it is equallyimportant that thorough inspections ofseat tracks and locking mechanisms arecarried out during maintenance. Cessnaintroduced Service Bulletin SEB89 inApril 1989 which provides for theinstallation of secondary seat stops on thepilot’s seat to limit the amount ofrearward travel in the event that theprimary seat lock fails. CAA NewZealand also issued AirworthinessDirectives for Cessna 100 and 200 Series

Loose Front-Seat LapBeltsDuring operation in turbulence, orduring sudden deceleration, the lap belttension was being loosened by the


t is no secret that inflight icingcompromises the function of airfoils.

1) reliance on aerodynamically balancedelevators without power boosting,

2) very efficient flaps,

3) non-tr immable stabilizers inconjunction with efficient airfoils, and

4) relatively small stabilizers.

Many airplanes are susceptible totailplane icing, but these fourcharacteristics are most common amongthe newer turboprop designs and areparticularly found in those airplanesdesigned for commuter operation. In fact,the FAA has issued nine ADs against sixairplanes in this category: the YS-11, theBAe Jetstream 3101, the ATR 42, the

airplane provides longitudinal stability bycreating downward lift to compensate forthe downward pitching moments of thewing and fuselage. In cruising flight, thosepitching moments are relatively small sothat the required (downward) lift can beproduced by the tail with a minimal(downward) angle of attack. During theapproach phase of flight, the required(downward) angle of attack on the tailchanges considerably.

Second, when the flaps are extended, thewing center of lift moves aft, increasingits downward pitching moment. Further,when the flaps are extended, thedownwash over the horizontal tail isincreased, which creates a higher(downward) angle of attack when the tailneeds to produce greater (downward) lift.Due to these combined effects, airplaneswith very efficient flaps and relativelysmall stabilizers may operate close tomaximum CL at the tail on finalapproach with flaps extended. In thatcondition, even a small amount of icecould cause the tail to stall.

Third, tail surfaces are smaller than wingsurfaces and, therefore, accumulate icemore efficiently. And, any given thicknessof ice will have a more adverse effect onthe tail due to its smaller leading-edgeradius and the ratio of thickness to chordlength. There are reports of ice accretionon tailplanes three to six times thickerthan ice on the wing and two to threetimes thicker than ice on the more visiblewindshield-wiper arms or some otherprotrusion. Many pilots routinely allowone inch of ice to accumulate on thewing leading edge before operating theboots. In such cases, as much as three tosix inches of ice could have accumulatedon the tail, and that ice may not be shed.Remember too, that even equalaccumulations of ice will have a greatereffect on the tail.

And while the icing effects discussed inthis article can affect virtually anyairplane, newer turboprop designs in thelightweight to mid-weight category withsophisticated computer-designed wingsseem to be the most vulnerable.

Elevator EffectsIn recent years, a number of accidentsand incidents have occurred involvinguncommanded airplane pitch downduring or shortly following flight inknown icing conditions. These incidentsalmost exclusively involve airplanes withthe following design characteristics:

Saab SF-340A, the Embraer 110 and theCessna T-303.

Turboprops are thought to be moreprone to tail-icing problems because oftheir operating environment at loweraltitudes and speeds where ice-avoidanceoptions are limited.

Research in this area is far from complete,and many of the conclusions and actionsare, necessarily, anecdotal.

Loss of elevator effectiveness in icingconditions is the result of severalinterrelated factors:

First, recall that the horizontal tail of an

By Dan Manningham

IIn all cases, ice accumulation reduces theefficiency of an airfoil so that its abilityto produce lift is decreased and its stallspeed is increased. Ice is a detractor to allairfoils at all times and has serious safetyimplications.

Traditional icing cautions have focusedon the effects of wing icing, such asreduced lift and increased stall speed. Inrecent years, a new generation ofairplanes has demonstrated susceptibilityto control problems due to icing. Theaerodynamic logic is identical, but theresults are far different.


Fourth, the tail can accumulate significantamounts of ice before the wingaccumulates any. Several accidentairplanes were found with inoperativetailplane ice-protection systems, or thetail ice-protection switch not in the “on”position. In addition, when the tailplaneis immersed in the propwash, it may besusceptible to icing at static airtemperatures above freezing because ofadiabatic cooling in the acceleratedpropwash air.

One more aerodynamic principle in theloss of elevator effectiveness in icingconditions would apply to any airplane,and it is an important concept. The(negative) angle of attack on the tailplanefor any given flap setting increases withspeed. It is the reverse of what happensto the wing. All other things being equal,at faster speeds, a wing will have a lowerangle of attack, which lowers the noseand raises the tail. When the tail is raisedin this fashion, it will have a higher(negative) angle of attack and beoperating closer to a stall.

The classic tailplane icing accident orincident occurs (but is not limited to) arelatively new turboprop design in thelightweight to medium-weight category.It occurs during, or shortly after, exitingicing conditions, and it occurs on the finalapproach when full flaps are selected. Atthat point, the combined effect of tail iceand increased flaps produces a tail stall.When the tail stalls, it can no longercompensate for the wing’s (downward)pitching moment, and the airplanepitches over abruptly. When it does, theyoke may be snatched abruptly forwardto the instrument panel.

But, there is an important point here:In almost all cases, there is still adequateelevator-control force available to recoverand control the airplane, although stickforces will be excessive. Pilots mayhave to apply as much as 100 poundsof pull force to recover pitch control.Unfortunately, when tail stall occurs atlow altitude, recovery may not be possiblebefore ground contact.

Loss of elevator effectiveness is aparticular risk in certain airplanes inicing conditions on final approach. Youcan minimize your risk by checking withyour manufacturer and the FAA forapplicable operating procedures. Inaddition, consider these guidelines:

Source: U.S. Air Force

ICING UNDER A WARM FRONT

ICING ZONES ALONG A COLD FRONT

ICING ZONES ALONG AN OCCLUDED FRONT

Limit of Heavy Ice

Ice Cloud

No Icing

Warm Air

0˚C

Water CloudWarm Front

Freezing Rain and Sleet

Falling Snow (No Icing)

Possible Flight PathSnow Falling ThroughIce and Water Cloud

Water CloudsLight Icing

Cold Air

Frontal S

urface

30,000

Ice and Water Cloud

Freezing Level3,000

Ice Cloud

30,000

10,000

0˚C

0˚C

Surface

Flight Path

Cumulus

Ice and Water20,000

Cirrus

Limit of Heavy Ice

Cold Front

Water Clouds

Cumulonimbus

Limit of Heavy IceIce Cloud

Warm Air

Coldest Air

Stratocumulus

Freezing Rain

Cool Air

30,000

Above Freezing Temperature


• Never fly into known icing conditionswith inoperable anti-icing or deicingcomponents, especially thoseassociated with the tail.

• When you observe ice on the wings,the windshield-wiper arm or someother protrusion, assume that evenmore ice has accumulated on thetail—a lot more—and that it will havea disproportionate effect.

suffered a roll upset over Roselawn, Ind.during descent, after holding in icingconditions. During the hold, the airplanewas flown with flaps extended and theautopilot engaged. Both of thoseconditions—in the presence of whatwas later found to be severe icing

droplets are no larger than 40 microns.

Larger droplets have greater inertia andproportionately less drag, so they travelfarther back along the chord line, covera larger area and spread the iced areafarther back on the wing. A case in point:Water droplets over Roselawn thatHalloween night were larger. In fact,compared to 40 microns, they weremonsters, up to 10 times larger.

One result of the Roselawn accident wasnew awareness of what are now calledSupercooled Large Droplets. SLD canoccur in several forms, with droplet sizesas large as 4,000 microns—100 timeslarger than the droplet size assumed byFAA certification. When your airplaneis subjected to an environment of SLD,icing can lead to roll-control problemsin three distinct ways:

First, at reduced speeds, ice from freezingdrizzle can form sharp-edged ridges overa large chordwise expanse of the wing’slower surface and fuselage. This buildupincreases drag, which reduces the speed,which requires an increase in angle ofattack, which produces more drag, andso on. This trend then can lead to a

Inflight icing has always been a problemfor aircraft, but recently the scope and intensity

of that problem have expanded.

• When you are in icing conditions, orhave just left icing conditions, makethe landing approach with somethingless than full flaps. Check with yourmanufacturer, but in most cases halfflaps is about right.

• Make final flap selections at least 1,000feet above ground level. Make thoseflap selections in small increments andre-trim between each one.

• When selecting flaps in icingconditions, leave your hand on the flapselector until the flaps reach theintended position. If the airplanepitches down when flaps are extended,immediately return the flap handle toits last position.

• When you suspect airfoil icing, becautious about adding airspeed for thefinal approach to compensate fordegraded aerodynamic efficiency ofthe wings. Each knot of speed addedto avoid wing stall will put you oneknot closer to tail stall. It is an either/or situation, so fly the approach by thenumbers with a firm grip on thecontrols.

• When icing conditions prevail on theapproach, fly the airplane manually.Use of the autopilot/auto-couplerwill mask the changes in control forcethat telegraph the presence of tail ice.

• If you do encounter pitch-over onfinal approach, muscle the yoke back,and it will provide adequate controlauthority in almost all cases.

The root problem is not control

authority but hinge moment, and youcan override it with enough pull force.

Tailplane icing is a real threat—especiallyto mid-size, propeller-driven airplanes.And while the problem isn’t new, ourunderstanding of it is.

Ice-Induced Roll UpsetsOn Halloween night, 1994, an ATR 72operating as American Eagle Flight 4184

conditions—contributed to the eventualupset and loss of control. This accidentwas a landmark tragedy that ultimatelyexposed a pernicious type of inflighticing previously not understood.

FAA icing certification has traditionallyassumed a maximum droplet diameter of40 microns. Water droplets of anyspecified size have predictable inertia anddrag properties that determine their travelalong the wing chord line. Thus, anygiven droplet size ultimately defines thesize of ice-protection systems. Currently,ice-protection systems are designed tocover that portion of the airfoil on whichice would be expected to form if the

conventional stall that is normallyfollowed by roll-off.

Second, at higher speeds (lower anglesof attack), ice can form in ridges justforward of the ailerons. When such ridgesform, they can disturb the airflow overthe ailerons in such a way as to create animbalance in the aerodynamic forces overthose controls until the ailerons “snatch”or deflect of their own accord, causingthe airplane to roll.

When ailerons snatch, the control forcesin the cockpit are effectively reversed.Instead of having to exert force on thecontrol wheel to deflect the ailerons, youwill have to make the same effort on the


control wheel to hold the ailerons in aneutral position. Aileron snatch will causethe airplane to roll, but you can overridethat response by muscling the aileronswhere you want them with the controlwheel. It will require deliberate actionand some strength, but the airplane willprobably be controllable. You cananticipate aileron snatch in icingconditions when aileron forces becomenoticeably different, when there is any

All of this is conducive to airflowseparation at the tips that compromisesaileron effectiveness.

When you do suspect that aileroneffectiveness is (or may be) compromisedby severe icing conditions, take thefollowing precautions:

• Disconnect the autopilot and hand flythe airplane because the autopilot willmask important handling cues.

Reprinted with permission from theFebruary 1997 issue of Business &Commercial Aviation, Copyright 1997,The McGraw-Hill Companies. Allrights reserved.

extends back close to the propeller-blade roots is very likely caused bySLD. As with the wing, you canenhance this visual check by paintingthe spinners with a dark, flat paint.

• Check for granular ice crystals or clearice on the unheated portions of thefront or side windshields.

• Watch for any signs of unusualice coverage, including ice feathersor fingers that extend onto portionsof the airframe not normallycontaminated with inflight icing.

SLD is particularly hazardous at ambienttemperatures near freezing. Whenoperating in conditions near the freezingpoint, watch for the following visual cues:

1) Any sign of visible rain is a clearindication that droplet size is wellabove the certification assumption of40 microns.

2) Droplets that splatter or splash on thewindshield can be assumed to be SLD.Droplets of 40 microns or less are notindividually visible and will not appearon the windshield in such patterns.

3) Rivulets of water streaming acrosswindows is an indication of highliquid water content and should betreated as SLD.

4) Radar returns showing precipitationsuggest water droplets large enoughto be considered SLD for flight safetypurposes.

In all cases, be particularly vigilant forchanges in the control feel of the aileronsand elevator. Any perceptible change tothe normal control response is cause forserious concern.

SLD can quickly compromise theflightworthiness of your airplane bysubstantially affecting aileron and/orelevator effectiveness. No airplane iscertificated for flight in such conditions,and pilots should take every precautionto avoid and exit these conditions.

Inflight icing has always been a challenge,but now it appears that the problem isconsiderably greater than we thought.

SLD can occur in several forms, with droplet sizesas large as 4,000 microns . . .

oscillation or vibration, or when you canfeel buffeting in the wheel.

Third, loss of roll-control effectivenesscan result when ice forms ahead of theailerons and disrupts the airflow overthem in a way that reduces theireffectiveness. This is different from the“snatch” scenario in which aerodynamicbalance is disrupted but effectiveness isessentially retained. When ice forms infront of the ailerons in such a way as todegrade aileron effectiveness, thosecontrols will not produce the rollingmoments you expect. In the worst case,they may not produce adequate rollingmoments to control the airplane. This isthe most disastrous possible roll-controlproblem because the airplane may notbe controllable.

Finally, one further condition cancontribute to roll-control problems,although probably not cause themdirectly. On most turboprop or jetairplanes, ice will tend to accumulate onthe wingtips before it does on the roots.This happens because the wingtips aredifferent from the roots, and they arealmost certainly thinner. They may havea different camber and shorter chord, andthey may have some degree of washoutrelative to the root section. For all thesereasons, the wingtips will tend toaccumulate ice quicker, thicker andfarther aft. In fact, even identicalaccumulations will have a more adverseeffect on the tips due to the smaller chord.

• Immediately advise ATC and exit thearea/altitude, being careful to avoidany abrupt control inputs.

• Reduce the angle of attack byincreasing airspeed or selecting thefirst increment of flaps. If flaps areextended, do not retract them unlessyou can determine that the uppersurface of the wing is clear of ice.

Signs of Severe IcingRoll-control problems, in particular, havebeen clearly identified with flight in areasof SLD. Flight in SLD conditions shouldnot be continued, under any conditions,so you should take whatever means arenecessary to depart those conditionswhen encountered. True SLD conditionsare sufficiently hazardous that you shouldser iously consider declar ing anemergency if that is required to obtain aclearance away from them.

How can you tell if you are flying inenvironmental conditions of SLD?

• Check for any ice formation aft of thedeiced area on the upper or lowersurface of the wing. You can facilitatethis task by painting a portion of thewing immediately aft of the deicedarea in a dark, flat color, different fromthe color of the deicing boots, and byinstalling wing lights or using a high-powered flashlight.

• On turboprop airplanes, check for iceon the propeller spinner any fartheraft than the first few inches. Ice that


Many recent articles on tailplane icing drawattention to the apparent increased sensitivityof aircraft with high performance wings, typicalof modern commuter aircraft. Tailplane icingcan affect virtually any aeroplane, however, andthe following reports in a recent GASILmagazine (published by our opposite numberin the UK) highlight the need for vigilance inany aircraft. The aircraft type involved, thePiper Seneca, is also a popular training typein New Zealand.

These scenarios occurred in January 1997.

Airframe IcingThe aircraft was engaged in night flying,Whilst at FL40, in VMC on top, therighthand vacuum pump warning lightilluminated, so the instructor elected toreturn to his base airfield. They wererequired to join the hold at 4000 feetQNH, which coincided with a thicklayer of stratocumulus. The outside airtemperature was –5∞C and the aeroplanestarted to accumulate ice. The waterdroplets were tiny, and the ice accrualrate was very slow. The commanderelected not to activate the de-icing bootsfor fear of losing the second gyro pumpand by implication both artificialhorizons. Instead, he monitored the iceusing the wing-ice lamp. The ice wasaffecting only the extreme leading edgeof the wing and looked slightly largerthan a ragged sugar cube. Thecommander did not consider the smallamount of ice to constitute a handlinghazard.

Dur ing the outbound leg of theprocedure, the wing-ice light failed and,although the pilot had a small torch, thiswas ineffectual in further ice checks.During the inbound turn, the aircraftbroke cloud at about 2500 feet. Thestudent was flying the aircraft and,although he had been struggling tomaintain accuracy, he hadn’t passed anycomment on the feel of the aircraft.

After completing the landing checks, thedescent was commenced at 2000 feet onthe glideslope and flap 25 was selected.Almost immediately, the aircraft startedpitching down, and the instructor’sinstinctive reaction was to pull back withboth hands. The aircraft did not respondfor a few alarming seconds before

recovering. As the nose approached thehorizon, the aeroplane again pitcheddown hard and the commander selectedflaps up as he was pulling back, and againregained level flight. The aeroplane felttotally unstable in pitch with anoscillatory motion. He exercised the de-icing boots and almost immediately theaircraft felt normal.

He transmitted a PAN call informingATC that he had exper ienced anuncontrolled pitch down, but it nowappeared under control. The approachwas continued and a flapless landing wasmade.

The pitch down was quite severe, but thecommander found it impossible to recallheight/speed/attitude parameters. It ishighly probable that the landing gear andflap speeds were exceeded, and thecommander distinctly remembered thatthe pull-out from the second dive wasnot what he would wish to inflict on aSeneca.

After shut-down there was significant iceon the stabilator.

Shortly after details of this were reported,an instructor who had been flying a fewhours earlier that day reported thefollowing:

He had been asked to remain in the holdat 4000 feet QNH for approximately 25minutes. There was a stratus layer, base2400 feet with tops at 4200 feet and theOAT was –3°C at 4000 feet. The pilotnoticed that ice started to accumulate onthe leading edges in a granular openstructure. Due to the small water droplets,the rate of accretion was slow but steady,and there was minimal flow-back overthe leading edges. The student was failing

to carry out frequent icing checks, andthe commander allowed the ice toaccumulate, as the thickness was less thanthat required for de-icing boot operation.The aircraft was simulated asymmetric,and the student began to experiencedifficulty maintaining altitude. Afterprompting, he eventually maintainedlevel flight at an attitude 3 to 5 degreesnose-higher than normal, with anincrease of 5 inches of manifold pressureto the live engine to maintain indicatedairspeed.

The commander was surprised by thesignificant reduction in performance fora relatively small amount of ice accretion,and he was, therefore, using theopportunity to make a training point tothe student. However, a student passengerin the back advised him that there was alarge amount of ice on the stabilator.The structure of the stabilator ice wassimilar to that on the leading edgeof the mainplane, but with little flow-back and a more pronounced ‘beak’of approximately half an inch. Thecommander operated the de-icing boots,with complete success on the mainplaneleading edges. However, there was onlypartial clearance on the stabilator of about30 to 40 percent, and two furtheroperations of the boot were required toeffect a full clearance,

The aircraft was climbed to 5000 feet,out of icing conditions, for the remainingholds, but picked up moderate ice duringthe descent, which cleared with the bootsbut required a further inflation to fullyclear the stabilator.

The captain of the second aircraft pointedout that the degradation of performancewas considerable, given the amount of


Videos

Here is a consolidated list of safety videos made available byCAA. Note the instructions on how to borrow or purchase(ie, don’t ring the editors).

Civil Aviation Authority of New ZealandNo Title Length Year released

1 Weight and Balance 15 min 19872 ELBA 15 min 19873 Wirestrike 15 min 19874 Mountain Flying 15 min 19885 The Human Factor 25 min 19896 Single-pilot IFR 15 min 19897 Radar and the Pilot 20 min 19908 Fuel in Focus 35 min 19919 Fuel Management 35 min 199110 Passenger Briefing 20 min 199211 Apron Safety 15 min 199212 Airspace and the VFR Pilot 45 min 199213 Mark 1 Eyeball 24 min 199314 Collision Avoidance 21 min 199315 On the Ground 21 min 199416 Mind that Prop/Rotor! 11 min 199417 Fit to Fly 23 min 199518 Drugs and Flying 14 min 199519 Fatal Impressions 5 min 199520 Decisions, Decisions 30 min 199621 To the Rescue 24 min 1996

Miscellaneous individual titlesWorking With Helicopters 8 min 1996**re-release date

Civil Aviation Authority, AustraliaThe Gentle Touch (Making a safe approach and landing) 27 minKeep it Going (Airworthiness and maintenance) 24 minGoing Too Far (VFR weather decisions) 26 minGoing Ag — Grow (Agricultural operations) 19 minGoing Down (Handling emergencies) 30 min

The videos are VHS format and may be freely copied, but for bestquality obtain professional copies from the master tapes – see “ToPurchase” below.

The New Zealand titles are produced on a limited budget, the first 11using low-band equipment. Quality improves in later titles. Whiletechnical quality may not be up to commercial programme standards,the value lies in the safety messages.

To Borrow: The New Zealand tapes may be borrowed, free of charge,as single copies or in multi-title volumes. Vol A contains titles 1 to 8,Vol B titles 9 to 14, Vol D titles 15 onwards. The Australian programmesare on a multi-title tape, Vol C. Contact CAA Librarian by fax(0-4-569 2024), phone (0-4-560 9400) or letter (Civil AviationAuthority, PO Box 31-441, Lower Hutt, Attention Librarian).There is a high demand for the videos, so please return aborrowed video no later than one week after receiving it.

To Purchase: Obtain direct from Dove Video, PO Box 7413,Sydenham, Christchurch. Enclose: $10 for each title ordered; plus$10 for each tape and box (maximum of 3 hours per tape); plus a $5handling fee for each order. All prices include GST, packaging anddomestic postage. Make cheques payable to “Dove Video”.

Publications0800 800 359 — Publishing Solutions, for CA Rules and ACs, Part 39Airworthiness Directives, CAA (saleable) Forms, and CAA Logbooks.Limited stocks of still-current AIC-AIRs, and AIC-GENs are also available.Also, paid subscriptions to Vector and Civil Aircraft Register.0800 500 045 — Aviation Publishing, for AIP documents, including PlanningManual, IFG, VFG, SPFG, VTCs, and other maps and charts.

Accident Notification24-hour 7-day toll-free telephone

0800 656 454CAA Act requires notification

“as soon as practicable”.

ice accretion, and the loss of performanceoccurred well before the ice hadaccumulated to the recommendedthickness for de-icing boot operation.The ice was thicker on the stabilator,probably due to the increased energyimparted to the airflow by the propellers.Worryingly though, the ice did not clearimmediately from the stabilator, despitefull clearance from the main wing leadingedges. At night, it is almost impossible tosee the stabilator.

[UK] CAA CommentIt would appear from the above thatcertain combinations of temperature andsuper-cooled water droplets produce thisspan-wise accumulation of ice, similar inlooks and effect to stall strips fitted tosome aircraft. It is likely that tailplanes,in the influence of prop-wash, are subjectto higher mass flow and therefore rates

of icing higher than the wings. As aconsequence, pilots can misjudge theprobability of tailplane stall when usingice accretion on the mainplane as thecriterion. The severe pitch-down whenflaps are selected, particularly with theCessna 400 series, has been highlightedin GASIL in the past.

Trim Tab IcingWhilst simulating an engine failure, theaircraft climbed to FL50 through aninversion at a constant –4°C throughout.The aircraft was in cloud for some 10minutes, and light ice accretion occurredwith a maximum of about 5 mm of rimeice on the wing leading edge, withapproximately 8 mm on the OAT probe,fuel cap, leading edges, etc. With full leftrudder trim applied, about 75 percent leftrudder travel was needed to sustainbalanced flight at 100 knots. On levelling

out in clear air (–4°C) the pilot wasunable to move the rudder trim. Hesuspected that it had frozen at full travelor otherwise jammed. Even maximummanual force would not release it. Afteran uneventful landing, where the OATwas still –2°C, the aircraft was takento the maintenance organisation forinspection.

After landing, 5 to 8 mm of ice was stilladhering to the airframe projections. Therudder trim was freed using manualrudder trim application after taxiing forthree minutes. The pilot inspected thetrim actuator rod which is on thelefthand side of the rudder surface, wherea small, 5 to 8 mm, knob of ice was stilladhering to the hinge attachment pointbetween the rod and the trim surface.This and other ice was easily removedbefore the next flight.

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LOOKOUT!How many helicopters did you see on our front cover?

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