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TERPS for PILOTS John Andrick BPT, Inc. 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. Reason we’re not going too deep: { ln { Θ descent = tan-1 r + alt r + THRe + TCH }. r D fix }. 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 180 π 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) 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 VFR Obstacle Clearance 1000 feet 4000 feet IFR Obstacle Clearance – Enroute and initial approach segments Primary OC area Secondary OC area 500 feet 2 Miles IFR ROC 1000 feet 8 Miles Federal Airway or Initial Approach Secondary OCA – 2 miles Primary OCA – 8 miles IFR Obstacle Clearance – Intermediate, Final, and Missed Approach segments IFR ROC Secondary OC area (width varies) Primary OC area (width varies) General View – Final Approach Segment Primary OC area Secondary OC area 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. 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) Level OCS with Constant ROC - Enroute ROC OCS Segments of an Instrument Approach #1 IF FAF MAP MAF Level OCS with Constant ROC - VOR Approach IAF IF FAF 1,000 ft Stepdown MAP 500 ft 250 ft 250 ft Segments of an Instrument Approach #2 LOC IF FAF DH MAF Sloping OCS (Used for precision approaches, LPV approaches, and departure procedures). NOT USED FOR LNAV/VNAV approaches! VNAV does not provide obstacle clearance! For approaches, OSC slope = 102 / glideslope angle or glideslope angle = 102 / OCS slope ROC DH (HAT) OCS Those Darned Trees! Four solutions for the problem of obstacle penetration – from worst to best…. ROC DH (HAT) OCS Solution #1 – Increase the DH (The worst solution – and only allowed for existing obstacles) OCS Solution #2 – Increase the OCS angle This requires increasing the Glidepath angle – possibly reducing the airport utility. OCS Solution #3 – Displace the Runway Threshold Reduces the effective length of the runway for landing – reducing the airport utility New Threshold OCS Solution #4 – Best - Remove the Obstacle The most permanent solution DH (HAT) OCS The Bigger Problem (most of the time) (Precision Approach shown) What’s the solution? OUCH! ROC DH OCS Airport Solution #1 – Increase DH or MDA This solution increases the ceiling and visibility minimums for all aircraft on the approach ROC DH OCS Airport Solution #2 – Increase OCS Angle Missed approach requires a minimum climb of XXX feet per NM to XXXX. If unable to meet climb gradient (options) (This solution may limit the type of aircraft able to use the approach). ROC DH OCS Airport Why are the Non-Precision Approach minimums higher than expected? It often has to do with the location of the MAP ROC DH OCS Airport Why are the Non-Precision Approach minimums higher than expected? You get much closer to the airport (and the obstructions in the missed approach area) on the non-precision approach Remember! VNAV indications and VDP points don’t guarantee obstruction clearance (but VASI and PAPI do) FAF MAP OCS Airport 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….. Thanks for Listening • Questions ?