FAA Instrument Flight Instructor (FII)IFR Procedures and ApproachesHard
On a nonprecision approach, the FAF crossing altitude is 2,400 feet MSL and the MDA is 780 feet MSL. The distance from the FAF to the missed approach point is 4.4 NM, and the aircraft's groundspeed on final is 100 knots. What is the approximate required rate of descent to reach the MDA at the MAP?
- AAbout 460 feet per minute
- BAbout 615 feet per minute
- CAbout 700 feet per minute
- DAbout 550 feet per minute
Show answer & explanationAnswer & explanation
Correct answer: B. About 615 feet per minute
Altitude to lose = 2,400 − 780 = 1,620 feet. Descent gradient = 1,620 ft ÷ 4.4 NM ≈ 368 ft/NM. At 100 knots groundspeed, the aircraft covers 100/60 ≈ 1.667 NM per minute. Required descent rate = 368 ft/NM × 1.667 NM/min ≈ 614 feet per minute.
Why the other options are wrong
- A. 460 fpm is too shallow and would not reach MDA by the MAP.
- C. 700 fpm overstates the descent rate needed for this altitude loss and distance.
- D. 550 fpm understates the required gradient for this distance/altitude loss.
Nonprecision Approach Descent Rate Calculation
The rate of descent needed on a nonprecision final segment is found by dividing the altitude to lose by the distance to the MAP to get a gradient (ft/NM), then multiplying by groundspeed in NM/min.
- Altitude loss = FAF altitude minus MDA
- Gradient = altitude loss ÷ distance (NM)
- Descent rate = gradient × (groundspeed ÷ 60)
- Steeper gradients or higher groundspeeds require faster descent rates
Memory trick: Drop the feet, divide by miles, multiply by speed per minute