AVIATION OCCURRENCE REPORT LOSS OF PROPELLER ......It is not the function of the Board to assign...

AVIATION OCCURRENCE REPORT

LOSS OF PROPELLER IN FLIGHT AND CABIN DEPRESSURIZATION

INTER-CANADIENATR 42-300 C-GIQV

VAL D'OR, QUEBEC 53 mi SE13 MARCH 1994

REPORT NUMBER A94Q0037

The Transportation Safety Board of Canada (TSB) investigated this occurrence for the purpose ofadvancing transportation safety. It is not the function of the Board to assign fault or determine civil orcriminal liability.

Aviation Occurrence Report

Loss of Propeller in Flight and Cabin Depressurization

Inter-CanadienATR 42-300 C-GIQVVal D'Or, Quebec 53 mi SE13 March 1994

Report Number A94Q0037

Synopsis

The aircraft, with 26 occupants on board, was on a flight from Val D'Or Airport, Quebec, to MontrealInternational (Dorval) Airport, Quebec. At about 17,000 feet above sea level, the No. 2 blade of theright propeller fractured in flight and penetrated the fuselage, causing a depressurization of the cabin. The crew members executed the required emergency procedures and landed at Dorval without furtherincident.

The Board determined that corrosion pitting had occurred on the surface of the taper bore of the No. 2blade as a result of water combining with chlorine deposits on the cork in the taper bore. The chlorinewas associated with the bleaching of the corks during their manufacture. One of the corrosion pits wasthe point of origin of the fatigue cracks that caused the propeller blade to fracture.

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TABLE OF CONTENTS

TRANSPORTATION SAFETY BOARD iii

Table of ContentsPage

1.0 Factual Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 History of the Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.2 Injuries to Persons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3 Damage to Aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3.1 Right Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.3.2 Fuselage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.4 Personnel Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4.2 Flight Crew . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4.3 Flight Attendant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4.4 Crew Training in Cockpit/Cabin Coordination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.4.5 Cockpit Resource Management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.5 Aircraft Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.5.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

1.5.2 Right Engine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5.3 Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5.3.1 Right Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5.4 Propeller Blade . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5.4.1 Blade Manufacture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1.5.4.2 Blade Balancing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.5.4.3 Corks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.5.4.4 No. 2 Blade Fracture Surface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.6 Meteorological Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.7 Aids to Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.8 Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

1.9 Aerodrome Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.9.1 Emergency Response Services Deployment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.10 Flight Recorders . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.10.1 Cockpit Voice Recorder (CVR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.10.2 Flight Data Recorder (FDR) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

1.11 Survival Aspects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.12 Tests and Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.12.1 Study on Fatigue Cracks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.12.2 Study on Cause of Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.13 Additional Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.13.1 Similar Occurrence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

TABLE OF CONTENTS

iv TRANSPORTATION SAFETY BOARD

1.13.2 External Examinations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.13.3 Emergency Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

1.14 Useful or Effective Investigation Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

1.14.1 Search for Reduction Gearbox and Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.0 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2 Flight . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2.1 Absence of Visual and Sensory Indications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.2.2 Crew Performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3 Propeller Separation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.4 Fuselage Damage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

2.5 Corrosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

2.6 Blades . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3.0 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.1 Findings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

3.2 Causes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

4.0 Safety Action . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

4.1 Action Taken . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

5.0 AppendicesAppendix A - Photographs of Aircraft . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Appendix B - List of Supporting Reports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Appendix C - Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

FACTUAL INFORMATION

TRANSPORTATION SAFETY BOARD 1

1.0 Factual Information

1.1 History of the Flight

On 13 March 1994 at 0957 eastern standardtime (EST1), an ATR 42, registrationC-GIQV, Inter-Canadien regular flight 1678,departed Val D'Or Airport, Quebec, en routeto Dorval Airport, Quebec. The aircraft, withtwo pilots, one flight attendant and 23passengers on board, was on an instrumentflight rules (IFR2) flight.

The aircraft took off from runway18 in Val D'Or. The co-pilot occupied theright-hand seat and was flying the aircraft. TheATR 42 was cleared to climb to flight level 210and proceed on airway V372 to the MirabelVHF omni-directional range (VOR3). Shortlyafter take-off, the crew engaged the autopilot(A/P) at 3,000 feet above sea level (asl).

The climb was routine up to about17,000 feet asl, when a violent explosion rockedthe aircraft and the cabin depressurized. TheCONTINUOUS REPETITIVE CHIMEwarning sounded in

1 All times are EST (Coordinated Universal Time (UTC)minus five hours) unless otherwise stated.

2 See Glossary for all abbreviations and acronyms.

3 Units are consistent with official manuals, documents,reports and instructions used by or issued to the crew.

the cockpit, and at the same time the masterwarning light and cabin excessive altitude lightilluminated. The crew observed that the rightengine parameters indicated a total loss ofpower.

Nine seconds after thedepressurization, the pilot-in-commandassumed control of the aircraft and disengagedthe A/P. He aborted the climb, commenced a

descent, and maintained speed. The enginefailure procedure and single engine checklistwere completed during the descent. Theco-pilot contacted Montreal Area ControlCentre (ACC) and advised the controller thatthe aircraft had experienced an engine failureand requested clearance to descend to15,000 feet, then to 11,000 feet.

The co-pilot pulled fire handle No. 2after visually confirming the damage to theengine and observing a fuel leak. The cabinexcessive altitude checklist was then completed. Three minutes after the occurrence, the crewdeclared an emergency with the Montreal ACC.

About seven minutes after the cabindepressurization, the co-pilot visuallyconfirmed the structural damage in the cabin. The pilot-in-command felt it was preferable tominimize the number of turns in order toreduce the risk of further structural damage. The crew considered the position of theaircraft, the weather, the available airports, theemergency services available, the knowndamage to the aircraft, the flying stability of theaircraft, and the flying time to possibledestinations. After noting the damage andassessing the situation, the pilot-in-commanddecided to continue the flight to Dorval. Atthat time, the aircraft was 36 minutes flyingtime from Val D'Or, 39 minutes from Mirabeland 44 minutes from Dorval.

At 1028 EST, the aircraft initiated adescent toward 9,000 feet asl and maintainedthat altitude, which was above the cloud layer,until it entered the Montreal terminal zone. The pilot-in-command requested thatemergency response services (ERS) be placedon alert at Dorval and Mirabel airports. Theaircraft was aligned with the instrument landingsystem (ILS) for Dorval runway 06L by radarvectors. It landed without further incident at1116 EST.

1.2 Injuries to Persons

Crew Passengers Others Total

Fatal - - - -Serious - - - -

FACTUAL INFORMATION

2 TRANSPORTATION SAFETY BOARD

Figure 1 - Blade Trajectory

Minor/None 3 23 - 26Total 3 23 - 26

Two passengers felt ill and experienceddiscomfort in their ears as a consequence of thecabin depressurization. Shortly after thelanding, the airline conveyed them to hospital,where they were given a medical examination. Their discomfort was of brief duration andthere was no permanent damage to their ears.

1.3 Damage to Aircraft

The damage was confined to the right side ofthe aircraft, aft of the propeller disc.

1.3.1 Right Engine

The front portion of the engine, beginning atthe air inlet, separated from the remainder ofthe engine, and its three mounts were torn awayfrom the titanium nacelle structure. The tworear mounts supported the rear of the engine. Six of the eight bolts securing the engine to therear mounts sheared off. (SeeAppendix A.)

1.3.2 Fuselage

The top of the No. 2 blade punctured thefuselage as the blade passed on its trajectorytoward and beneath the aircraft. A vertical cutmeasuring 104 cm by 2.5 cm was observedbetween stations 9157 and 9333 on the rightside of the fuselage. The seat adjacent to thevertical cut was partially cut. Two landing gearhydraulic lines mounted under the floor wereslightly bent. (See Figure 1 - Blade Trajectory.)

Some debris penetrated the uppersurface of the landing gear nacelle and cut thepneumatic de-icer between the engine and thefuselage. Several scrapes were also observed onthe painted surface of the fuselage. (SeeAppendix A.)

1.4 Personnel Information

1.4.1 General

Captain FirstOfficer

Age 34 32Pilot Licence ATPL ATPLMedical Expiry Date 01 Nov 94 01 Nov 94Total Flying Time 8,733 hr 6,000 hrTotal on Type 4,000 hr 4,000 hrTotal Last 90 Days 165 hr 180 hrTotal on Type Last 90 Days 165 hr 180 hrHours on Duty Prior to Occurrence 3.5 hr 3.5 hrHours off Duty Prior to Work Period 60 hr 72 hr

1.4.2 Flight Crew

The pilot-in-command and co-pilot werecertified and qualified for the flight inaccordance with existing regulations. Bothwere experienced on the ATR 42 and had beenflying the aircraft type for several years.

1.4.3 Flight Attendant

A flight attendant was also responsible for thesafety and comfort of passengers on board theaircraft. She had received her initial training onthe ATR 42 in December 1988, and had

FACTUAL INFORMATION


successfully completed all courses,examinations, and practices required by thecompany and approved by Transport Canadaduring the year preceding the accident.

1.4.4 Crew Training in Cockpit/Cabin Coordination

The three crew members had received trainingto improve coordination and communicationbetween flight crews and flight attendants inemergencies and unusual situations. Thistraining is not required by Transport Canada.

1.4.5 Cockpit Resource Management

The pilot-in-command and co-pilot had taken acockpit resource management (CRM) course,which concentrates on achieving optimumutilization of the resources available to ensure asafe and efficient flight. This training is notrequired by regulation.

1.5 Aircraft InformationParticulars

Manufacturer Avions de transport régionalType ATR 42-300Year of Manufacture 1989Serial Number 203Certificate of Airworthiness (Flight Permit) validTotal Airframe Time 8,276.7 hrEngine Type (number of) PW120 (2)Propeller/Rotor Type Hamilton Standard (number of) 14SF-5 (2)Maximum Allowable Take-off Weight 16,704 kgRecommended Fuel Type(s) Jet BFuel Type Used Jet B

1.5.1 General

Inter-Canadien had been operatingC-GIQV since 08 September 1990. Theaircraft had never been involved in an accidentor struck by lightning. The weight and centreof gravity were both within the prescribedlimits. The aircraft was certified, equipped andmaintained in accordance with existingregulations and approved procedures. Allpertinent service bulletins and airworthinessdirectives had been completed.

The change to the aircraft's centre ofgravity caused by the separation of thepropeller was inconsequential. Although six ofthe eight bolts securing the engine to the rearmounts sheared off and the engine's three frontmounts were torn away, the engine remained inits frame. It is unlikely that there was any

possibility of the engine separating from theaircraft.

1.5.2 Right Engine

The engine had 8,603 hours total time inservice and 3,705 hours since overhaul.

The engine fractured at the mountsecuring the turbine to the reduction gearbox. The reduction gearbox auxiliary componentsremained attached to the engine by their linesand electrical harnesses.

The engine teardown and analysis didnot reveal any discrepancies prior to thepropeller rupture. Damage to the enginecorresponds to damage caused byinstantaneous overload.

1.5.3 Propeller

This type of composite propeller is used bymany aircraft manufacturers, on over2,000 aircraft. These propellers haveaccumulated over 17 million flying hours as ofthe occurrence date.

1.5.3.1 Right Propeller

The propeller was found on the frozen surfaceof the Cabonga Reservoir, Quebec. The No. 1,3 and 4 blades were twisted and their surfacesshowed substantial damage. The No. 2 blade(serial number 856922) was fractured at station22.27. The tip of the No. 2 blade was notfound.

The operator had inspected the rightpropeller three days before the occurrence andthe No. 2 blade retaining ring spacer clearancehad been set. Examination of the bladesurfaces did not reveal any discrepancies.

1.5.4 Propeller Blade

The blade is 188.55 cm long, with a chordwisedimension of 30.50 cm; its surface is fibreglass. The spar is bored out from the root to a depthof 56 cm.

The No. 2 blade was manufactured inDecember 1987. It had 12,238 hours total timesince new (TTSN) and 4,748 hours time sincemajor inspection (TSMI).

FACTUAL INFORMATION


Figure 2No. 2 Blade

1.5.4.1 Blade Manufacture

The blade spar was forged from 7075-T73aluminum alloy. A characteristic of this alloy isthat it inhibits stress corrosion cracking. Thefluorescent particle inspection (FPI) methodwas used to check the spar for cracks. Themanufacturer has never found cracks in thebore using this method. The spar and borewere then treated against corrosion; they wereanodized and coated with Alodine 1200solution.

Before April 1987, shotpeening wasused to enhance the blade material fatiguestrength in the taper bore area. HamiltonStandard evaluated the process and determinedthat shotpeening the bore was superfluous forthis type of blade. The No. 2 blade wasmanufactured in accordance with approvedprocedures after this shotpeening procedurewas discontinued.

1.5.4.2 Blade Balancing

The blades undergo static balancing with leadwool placed in the bore after manufacture,major inspection, or repair.

To avoid damage to the internal surfaceof the bore, the lead wool is packed with aseries of steel rods tipped with brass. (Apneumatic driver is occasionally used with thesteel rods to remove the lead.) The lead is thensecured in the bore with a cork placed againstthe lead.

The No. 2 blade was balancedfollowing the last major inspection. At thattime, the bore was visually inspected with thecork in place. The inspection can be donewithout removing the cork; in fact, it wasrecommended that the lead not be removed ifpossible. No signs of corrosion were observedin the bore.

1.5.4.3 Corks

There are no manufacturing specifications forthe corks; however, the corks meet laboratory-grade specifications. They were cooked insteam and washed in chlorinated water. Oninstallation, a V-shaped cut was made along thelength of the cork to allow air to escape. Examination of the corks established thatchlorine was present on their surface.

1.5.4.4 No. 2 Blade Fracture Surface

The fracture surface showed fatigue marksoriginating in the spar bore on the face side ofthe blade. Approximately80 per cent of the fracture surface exhibitedfatigue cracks; damage on the remainder of thefracture surface was attributable to overloadfailure. Metallurgical analysis revealed that acorrosion pit 0.1524 cm in the circumferentialdirection, 0.0762 cm into the material (radialdirection) and 0.1447 cm in the axial directionwas the point of origin of the fatigue crack. Tensile stresses were greatest on the face sideof the bore where the crack originated.

Four other superficial cavities werefound in the bore at the same station on thecamber side of the blade. The camber side ofthe taper bore was subjected to highcompression stresses in flight.

1.6 Meteorological Information

FACTUAL INFORMATION


A weather analysis was carried out by theQuebec Weather Centre of EnvironmentCanada. Western Quebec was under theinfluence of a low pressure system extendingfrom Parent, Quebec, to Maniwaki, Quebec. Associated with this system was an area of lightsnow covering all of western Quebec andcreating generally IFR conditions close to andsouth of the low pressure system.

Meteorological conditions at 1000 EST,15 minutes before the accident, were as follows:

- at Val D'Or, a ceiling of broken cloudat 800 feet and overcast at 1,500 feet,visibility reduced to three miles in lightsnow, temperature minus three degreesCelsius, dew point minus four degreesCelsius, and surface winds from 320degrees at three knots;

- at Dorval, ceiling overcast at 500 feet,visibility three miles in light snow,temperature minus six degrees Celsius,dew point minus eight degrees Celsius,and surface winds from 040 degrees at10 knots;

- at Mirabel, ceiling overcast at 700 feet,visibility four miles in light snow grainsand light freezing drizzle, temperatureminussix degrees Celsius, dew point minuseight degrees Celsius, and surface windsfrom 070 degrees at six knots.

At the time of the landing, theconditions at Dorval were: sky partiallyobscured, ceiling 500 feet above ground level(agl), visibility 1.5 miles in very light snowgrains and fog, winds northeast at seven knots. Turbulence was not considered to be animportant factor.

1.7 Aids to Navigation

Shortly after the depressurization, the pilot-in-command asked the controller for a radarvector to Dorval Airport to align the ATR 42with the runway 06L ILS. Although part of theflight had been conducted below the minimumen route

3 TESTRA is a French acronym. Roughly translated,it stands for Type of problem, Evacuation (whichexits), Signal to be given, Time, Relocation ofpassengers, Announcement to passengers.

altitude (MEA) of 10,000 feet, the aircraft'snavigational equipment functioned normallythroughout the flight. Although the aircraftwas below the MEA, it stayed above theminimum obstacle clearance altitude (MOCA)of 4,000 feet for most of the flight and was inno danger of colliding with any obstacles.

1.8 Communications

The air-to-ground communication systemsfunctioned normally during the flight. Air-to-ground communications were recorded onmagnetic tape by Air Traffic Services (ATS). The tapes were obtained for analysis.

The intercom system between thecockpit and the flight attendant also functionedproperly. However, after the depressurization,the ambient noise in the cabin made the publicaddress system practically inaudible. Somepassengers did not hear the pilots'announcements clearly. The flight attendantrepeated the pilots' messages to the passengersto ensure effective communications betweenthe crew members and passengers.

The flight attendant was serving thepassengers when the depressurization occurred. She immediately sat down in the aft jump seatand informed thepilot-in-command, via the intercom, that theforward portion of the right engine hadseparated from the aircraft.

Just after the depressurization, theflight crew and flight attendant coordinatedtheir actions to manage the unusual emergency. The flight attendant reported the damage sheobserved to the pilot-in-command and anemergency plan was immediately established. She noted that no passengers were injured andthat the fuselage was cut at seat 3D. Anemergency landing action plan (TESTRA3) wasestablished by the crew and flight attendant. She returned to the cabin and moved thepassengers sitting near the cut to a positionfurther aft.

The pilot-in-command kept the flightattendant and passengers informed of thesituation during the flight until the landing. All

FACTUAL INFORMATION


indications are that effective communicationswere established between the crew members.

1.9 Aerodrome Information

Dorval Airport is located on the western part ofMontreal Island. The municipalities of Dorvaland St-Laurent share the airport, and theirfirefighting services respond to emergencies. The airport also has an emergency responseservice (ERS) for first response.

Aerodromes are categorized accordingto the level of ERS response they provide. TheERS category provided is based on the lengthof the aircraft and the number of aircraftmovements. The longer the fuselage, thehigher the ERS category. With a higher ERS,the quantity offire-extinguishing agent available increases. The highest category is 9. The ERS categoryfor Val D'Or is 4; Dorval's is 8, and Mirabel's is9. A category of 5 is recommended for theATR 42. However, the ERS category can beup to two categories below the category of theaircraft.

Dorval Airport has three runways: onerunway 10/28 and two runways 06/24. Runway 06L, with a length of 11,000 feet, is thelongest.

1.9.1 Emergency Response Services Deployment

Dorval and Mirabel Airport ERS were placedon alert at the request of thepilot-in-command.

At 1025 EST, the shift supervisor in theDorval tower informed the ERS of theATR 42's situation and reported that itsestimated landing time was 1108 EST. Theemergency centre was put in operation at1030 EST. The Royal Canadian MountedPolice (RCMP), airport firefighters, MontrealUrban Community Police Service (SPCUM),City of Dorval fire department, Urgence-Santé,Inter-Canadien, and TSB were informed. At1050 EST, the Dorval fire department and ERSvehicles were in position to respond on runway06L.

The aircraft landed without furtherdifficulty and stopped on taxiway Echo, wherea damage assessment was carried out todetermine the risk of fire. No significant fuelleaks were found, and the aircraft was clearedto taxi to gate 43P, where the passengers

disembarked. There was no emergencyevacuation of the passengers from the aircraft.

1.10 Flight Recorders

The flight recorders were retrieved just after thepassengers disembarked. The recorders wereplayed back and analyzed at the TSBEngineering Branch Laboratory.

1.10.1 Cockpit Voice Recorder (CVR)

The CVR is a Fairchild model A100A. As itsrecording period is only 30 minutes, thematerial recorded at the time of the occurrencehad other information recorded over it and waslost.

1.10.2 Flight Data Recorder (FDR)

The FDR is a Sundstrand. The recording lastsapproximately 25 hours, during which time 43flight parameters are registered. Theparameters for the last 21 flights were recordedduring that period. Analysis of this datarevealed no anomalies prior to the bladefracture. The aircraft systems recorded by theFDR were operating within the prescribedlimits.

Since the commissioning of the aircraft,the Inter-Canadien maintenance departmenthas uploaded certain FDR data onto computerdisks on a daily basis. These data are analyzedto monitor engine performance and patterns. The analysis is also used to detect operationalirregularities in aircraft systems. Examinationof the data revealed that no prescribed limitswere exceeded.

1.11 Survival Aspects

When the No. 2 blade punctured the fuselage, itpartially cut the aluminum seat of seat 3D. (SeeFigure 1 - Blade Trajectory.) Seats 3D and 3Cwere unoccupied. Depressurization occurred atan altitude where the risks associated withdecompression sickness are minimal.

1.12 Tests and Research

1.12.1 Study on Fatigue Cracks

A crack propagation study is ongoing atHamilton Standard. The study involvescorrelating the flight parameters retrieved fromthe FDR and the fatigue tests done by themanufacturer, Hamilton Standard, with the

FACTUAL INFORMATION


striations observed on the fractured section ofthe No. 2 blade. This study provided additionalsupport to the 1,250 cycle blade ultrasonicinspection interval that Hamilton Standardaddressed in the Alert Service Bulletin 14SF-61-A74 dated 29 August 1994.

1.12.2 Study on Cause of Corrosion

Examination of the spar revealed nodiscrepancies related to its fabrication.

The physical evidence and the testsconducted by Hamilton Standard indicated thatwater combined with the chlorine on thesurface of the cork to produce an acidicsolution strong enough to corrode the anodiccoating and aluminum alloy.

Although there were five corrosion pitsin the bore, only the pit on the face side of theNo. 2 blade produced the fatigue cracks.

1.13 Additional Information

1.13.1 Similar Occurrence

On 30 March 1994, in Brazil, a similar bladefractured in flight. The fracture was caused byfatigue originating from a corrosion pit. It wasdetermined that a solution of chlorine, comingfrom the cork, and water probably producedthe corrosion in the bore where the fractureoriginated. The blade had 4,185 hours totaltime in service.

1.13.2 External Examinations

A visual examination of the exterior of theaircraft was carried out by the co-pilot. Thisexamination must be done after each crewchange.

No discrepancies related to thepropellers were reported by the pilots who hadflown the aircraft on the days preceding theaccident.

1.13.3 Emergency Procedure

There is no particular emergency procedure forthe event of a blade separating in flight.

1.14 Useful or Effective InvestigationTechniques

1.14.1 Search for Reduction Gearbox and Propeller

The blade broke 53 nm from Val D'Or Airport,over the Cabonga Reservoir and the LaVérendrye game reserve. This area isuninhabited and densely wooded. The area hasrelatively uniform topography and numerouslakes.

A ballistic study was conducted by theTSB laboratory to determine the area where thereduction gearbox and propeller could havefallen. The elements considered in the studyincluded the FDR data, radar data,meteorological information, and thedimensions, weights, and shapes of the missingparts. The reduction gearbox and propellerwere found less than 500 metres from theestimated point of impact.

FACTUAL INFORMATION


ANALYSIS


2.0 Analysis

2.1 Introduction

The following analysis concentrates on theflight, the aircraft, the propeller, and themanufacturing of the blades.

2.2 Flight

2.2.1 Absence of Visual and Sensory Indications

Because the point of origin of the fracture wasinside the bore, the fatigue cracks propagatedfrom the interior toward the blade surface. Itwas, therefore, impossible for the crew todetect any discrepancies during the externalinspection of the aircraft. Additionally, therewere no indications prior to or during the flightwhich could have enabled the flight crew toanticipate the fracture of the blade. Analysis ofthe FDR data for the occurrence flight and forprevious flights revealed no failures orabnormal vibrations prior to the blade fracture.

2.2.2 Crew Performance

Fracture of a propeller blade in flight isconsidered a highly improbable occurrence, asis the partial disintegration of an engine. Crewsare not specifically trained to deal with suchemergencies. In an emergency situation, thecrew will react in accordance with theprocedures practised during training. In theabsence of training or standard proceduresdictating how to deal with a particular situation,the crew must react by drawing upon theirknowledge and experience.

The crew reacted first to the cabindepressurization, then to the engine failure. The pilots were not fully aware of the situationuntil the flight attendant informed them thatthe forward portion of the engine hadseparated in flight and that there was a cut inthe fuselage. When it became evident that theyhad indeed lost the right engine, the co-pilot cutoff fuel to the engine by pulling fire handleNo. 2.

After stabilizing the aircraft andcontrolling the emergency, the crew assessedthe situation. Because the behaviour of theaircraft in horizontal flight was satisfactory andthe crew did not know the extent of thedamage to the aircraft, the pilot-in-commandfelt it was preferable to minimize the number ofturns in order to reduce the risk of further

structural damage. The crew took intoconsideration the position of the aircraft, theweather, the airport services available, theknown damage, the reactions of the aircraft,and the flying time to possible destinations. Analysis of ATS communications and thepilots' statements suggests that the decision tocontinue the flight to Montreal was taken nineminutes after the blade fracture.

2.3 Propeller Separation

When the blade separated, the forces inducedby the propeller imbalance on the three forwardengine mounts exceeded the ultimate limits ofeach support and of the reduction gearboxmount. This allowed the propeller andreduction gearbox to separate from the turbine.

2.4 Fuselage Damage

None of the propeller or reduction gearboxcomponents found showed traces of paint fromthe fuselage. All indications are that the No. 2blade fractured when in a position such that itstrajectory allowed it to penetrate and then passthrough the fuselage before following itscourse. The other damage to the aircraft wascaused by nacelle debris during the separation.

2.5 Corrosion

There were traces of chlorine in the corrosionpit at the point of origin of the No. 2 bladefracture. The chlorine was associated with thebleaching of the corks during theirmanufacture.

Chlorine deposits on the surface of thecork, in the presence of water, produce anacidic solution which can attack the anodiccoating on the aluminum and initiate superficialcorrosion pitting.

There were five corrosion pits in thetaper bore of the No. 2 blade. Only one of thepits observed had progressed to the pointwhere it initiated the fatigue fracture. This wasthe only pit on the face side of the blade bore. It is on this side of the blade bore, and at thisstation, that tensile stresses are greater than atany other point in the bore.

2.6 Blades

ANALYSIS


The blades on this type of aircraft aremanufactured in accordance with their FederalAviation Administration (FAA) certification.

The investigation revealed thatshotpeening as part of the blade manufacturingprocess was discontinued in April 1987. Shotpeening offered supplementary protectionin the form of reduced crack propagation in thearea of the residual compressive stress inducedby the shotpeening.

Corks have been used for many yearsto hold lead wool in place in blade bores.

Hamilton Standard had never observedthat corrosion had been initiated by the use ofcorks. Additionally, the taper bore was not anarea of the blade that was susceptible tocorrosion. Internal visual inspection duringmajor inspections was the only kind ofinspection required by the manufacturer forthis area.

The moisture necessary to initiate thecorrosion pitting must have been introducedwhen the cork was installed: that is, either at the7,500-hour major inspection or during themanufacturing process. However, it could notbe determined with certainty at which momentthe moisture was introduced.

CONCLUSIONS


3.0 Conclusions

3.1 Findings

1. The aircraft was certified, equipped andmaintained in accordance with existingregulations and approved procedures.

2. The blade was manufactured andinspected in accordance with themanufacturer's standards andprocedures.

3. The corks used in the taper bore arecovered with a chlorine deposit.

4. Water in the taper bore in contact withthe chlorine from the cork can producean acidic solution which can causecorrosion.

5. The fractured blade showed corrosion

pitting in the taper bore.

6. The inside of the taper bore of thefractured blade had not beenshotpeened during manufacture.

7. An inspection of the No. 2 blade threedays before the occurrence did notreveal any damage to the blade surface.

8. The 7,500-hour major inspection wasperformed using the procedures andmaterials specified by the manufacturer.

9. The fractured section of the bladepunctured the fuselage and caused thecabin depressurization.

3.2 Causes

Corrosion pitting had occurred on the surfaceof the taper bore of the No. 2 blade as a resultof water combining with chlorine deposits onthe cork in the taper bore. The chlorine wasassociated with the bleaching of the corksduring their manufacture. One of thecorrosion pits was the point of origin of thefatigue cracks that caused the propeller blade tofracture.

SAFETY ACTION


4.0 Safety Action

4.1 Action Taken

The Board issued an Aviation Safety Advisoryrequesting that Transport Canada confirm withHamilton Standard and the FAA that themeasures taken by Hamilton Standard meetCanadian airworthiness requirements.

Hamilton Standard was able to take thefollowing steps to prevent similar occurrences:

A - Field Actions:

1) Alert Service Bulletin 14SF-61-A73,dated 18 April 1994 (mandated byFAA Airworthiness Directive 94-09-06, effective date 02 May 1994),provided instructions to perform aone-time inspection of all 14SFblades using ultrasonic methods toinspect the taper bore foranomalies.

2) Alert Service Bulletin14SF-61-A74, dated 29 August1994, provided instructions for theperformance of a blade taper boreultrasonic inspection as describedabove every 1,250 cycles, or toperform a one-time removal of thetaper bore cork and visually inspectthat portion of the taper bore forpits for blades that had not beenshotpeened or had not had theirtaper bores inspected at HamiltonStandard's overhaul facility. Thecork removal/visual inspectionprocedure is addressed by ServiceBulletin 14SF-61-75. At the presenttime, the FAA is preparing anAirworthiness Directive to mandatethis bulletin.

3) Revision No. 8 to the HamiltonStandard Component MaintenanceManual 61-13-02, dated01 September 1994, includesinstructions for inspection andrepair of the blade taper bore areawhen the blade is returned to arepair facility. It also requiresshotpeening of the taper bore forblades not previously shotpeenedand mandates the use of new toolsto reduce the chance of damagingthe taper bore during lead wool

removal. It also deletes instructionsto install cork in the taper bore.

B - Manufacturing Actions:

1) Re-introduced shotpeening to bladetaper bores in May 1994.

2) Deleted cork installation in thetaper bores in May 1994.

3) Changed the sequence of stepsassociated with the manufacturingto prevent water being introducedinto the taper bore after lead woolis installed.

This report concludes the Transportation Safety Board'sinvestigation into this occurrence. Consequently, the Board,consisting of Chairperson, John W. Stants, and membersGerald E. Bennett, Zita Brunet, theHon. Wilfred R. DuPont and Hugh MacNeil, authorizedthe release of this report on 28 February 1995.

APPENDICES


Appendix A - Photographs of Aircraft

Propeller Damage to Fuselage

Engine as it was at Landing

APPENDICES


Appendix B - List of Supporting Reports

The following TSB Engineering Branch Laboratory reports were completed:

LP 042/94 - FDR Analysis;

LP 048/94 - ATR-42 Propeller Separation Analysis;

LP 049/94 - Propeller and Gearbox Analysis; and

LP 050/94 - Propeller and Gearbox Search.

These reports are available upon request from the Transportation Safety Board of Canada.

APPENDICES


Appendix C - GlossaryA/P autopilotATS Air Traffic Servicescm centimetre(s)CRM cockpit resource managementCVR cockpit voice recorderERS emergency response servicesEST eastern standard timeFAA Federal Aviation AdministrationFDR flight data recorderhr hour(s)IFR instrument flight rulesILS instrument landing systemkg kilogram(s)MEA minimum en route altitudeRCMP Royal Canadian Mounted PoliceSPCUM Montreal Urban Community Police ServiceTSB Transportation Safety Board of CanadaUTC Coordinated Universal TimeVHF very high frequencyVOR very high frequency omni-directional range

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