TERPS for PILOTS - PBPT · For approaches, OSC slope = 102 / glideslope angle or glideslope angle =...
Transcript of TERPS for PILOTS - PBPT · For approaches, OSC slope = 102 / glideslope angle or glideslope angle =...
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TERPS for PILOTS John Andrick
BPT, Inc.
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INTRODUCTION
• This course will introduce the pilot to elementary principles of obstacle analysis for the most popular instrument procedures today.
• We’re not going to get into the “nuts and bolts” of creating instrument procedures – even the feds disagree on some of this stuff!
• That means I probably cannot answer specific questions about specific approaches.
• The goal is to make you aware of the various metrics used in obstacle clearance analysis so you will understand the risk you’re taking if you depart from standard procedures.
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Reason we’re not going too deep:
Θ descent = tan-1 { r + alt r + THRe + TCH } . r
D fix } . { 180
π ln
Where: • Alt = FAF altitude • THRe = Threshold elevation in feet above sea level • r = radius of the earth at the FAF in feet • TCH = Threshold Crossing Height • D fix = Distance from FAF to MAP in feet
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DEFINITIONS
• Precision Approach - Approach with electronic vertical guidance that meets the requirements of ICAO Annex 10. • ILS and PAR (DH published)
• (Why not LPV? ICAO needs to move into the present!)
• Approach with Vertical Guidance - Approach with electronic vertical guidance that does not meet the requirements of ICAO Annex 10. • LPV, LNAV/VNAV, and LDA with Glideslope (DA published)
• Non-Precision Approach • Everything else (MDA published)
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Definitions – cont.
• OCS – Obstacle Clearance Surface • An imaginary plane determined by the highest obstacle within a defined
lateral or longitudinal space. No obstacles are permitted above the OCS.
• Can be level or sloping, depending on phase of flight.
• ROC – Required Obstacle Clearance • The minimum vertical separation needed between the OCS and the airplane.
• Can be constant, increasing or decreasing, depending on phase of flight.
• These concepts are familiar to the VFR pilot, but they are applied in a different way for IFR operations. • FAR 91.119
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VFR Obstacle Clearance
4000 feet
1000 feet
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IFR Obstacle Clearance – Enroute and initial approach segments
IFR ROC 1000 feet 500 feet
Primary OC area Secondary OC area
8 Miles 2 Miles
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Federal Airway or Initial Approach
Primary OCA – 8 miles
Secondary OCA – 2 miles
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IFR Obstacle Clearance – Intermediate, Final, and Missed Approach segments
IFR ROC
Secondary OC area (width varies)
Primary OC area (width varies)
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General View – Final Approach Segment
Secondary OC area
Primary OC area
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Standard Dimensions
The dimensions of the final approach trapezoid are defined by the type of facility used for lateral guidance in the approach: VOR – 30 miles long. Primary area is 2 miles wide at the facility and expands to 5 miles wide at the 30 mile point. Secondary widths are 0 to 1 mile. NDB – 15 miles long. Primary area is 2.5 miles wide at the facility and expands to 5 miles wide at the 15 mile point. Secondary widths are 0 to 1.34 miles. LOC/ILS/LP/LPV – 50,000 feet long. 1,400 feet wide at the narrow end (200 feet from the runway threshold) increasing to 2 nm wide at the 50,000 foot point. Secondary areas are 300 feet wide increasing to 2,500 feet. LNAV or LNAV/VNAV – No length specified. Primary width is 4 NM at the FAF decreasing to 1.2 NM at the MAP. Secondary areas are 1 NM wide.
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Standard ROC’s
• Enroute – 1,000 / 2,000 feet (possibly 1500/1700 feet with waiver)
• Initial Approach – 1000 feet
• Intermediate Approach – 500 feet
• Final Approach • NDB without FAF – 350 feet
• VOR without FAF or NDB with FAF – 300 feet
• LOC, LDA, LNAV, LNAV/VNAV, LP, VOR with FAF – 250 feet
• ILS and LPV – 200 feet HAT (we will not consider cat 2/3 in this course)
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Level OCS with Constant ROC - Enroute
OCS
ROC
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Segments of an Instrument Approach #1
IF FAF MAP MAF
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Level OCS with Constant ROC - VOR Approach
1,000 ft 500 ft 250 ft
250 ft
IF
FAF Stepdown
MAP
IAF
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Segments of an Instrument Approach #2
IF FAF DH MAF
LOC
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Sloping OCS
OCS
DH (HAT)
(Used for precision approaches, LPV approaches, and departure procedures). NOT USED FOR LNAV/VNAV
approaches! VNAV does not provide obstacle clearance!
ROC
For approaches, OSC slope = 102 / glideslope angle or glideslope angle = 102 / OCS slope
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Those Darned Trees!
OCS
DH (HAT)
ROC
Four solutions for the problem of obstacle penetration – from worst to best….
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Solution #1 – Increase the DH (The worst solution – and only allowed for existing
obstacles)
OCS
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Solution #2 – Increase the OCS angle
OCS
This requires increasing the Glidepath angle – possibly reducing the airport utility.
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Solution #3 – Displace the Runway Threshold
OCS
Reduces the effective length of the runway for landing – reducing the airport utility
New Threshold
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Solution #4 – Best - Remove the Obstacle
OCS
DH (HAT)
The most permanent solution
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The Bigger Problem (most of the time)
OCS DH
(Precision Approach shown)
ROC
OUCH!
What’s the solution?
Airport
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Solution #1 – Increase DH or MDA
OCS
DH ROC
This solution increases the ceiling and visibility minimums for all aircraft on the
approach
Airport
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Solution #2 – Increase OCS Angle
OCS
DH ROC
Missed approach requires a minimum climb of XXX feet per NM to XXXX. If unable to meet climb gradient (options)
Airport
(This solution may limit the type of aircraft able to use the approach).
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Why are the Non-Precision Approach minimums higher than expected?
OCS
DH ROC
Airport
It often has to do with the location of the MAP
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Why are the Non-Precision Approach minimums higher than expected?
OCS
MAP
Airport
You get much closer to the airport (and the obstructions in the missed approach area) on the non-precision approach
FAF
Remember! VNAV indications and VDP points don’t guarantee obstruction clearance (but VASI and PAPI do)
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Important Takeaways
• Follow established procedures!
• If you can’t maintain the required minimum climb gradient, you are not assured of adequate obstacle clearance!
• Min 200 feet per mile for Departures and Missed approaches – can sometimes be more
• Enroute performance minimums: • SL to 5000 feet – 150 ft./NM • 5000 to 10,000 feet – 120 ft./NM • Above 10,000 feet – 100 ft./NM
• Think long and hard about the wisdom of IFR flight if you can’t climb at these rates…..
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Thanks for Listening
• Questions ?