FAA Aircraft Dispatcher (ADX)Flight Planning and PerformanceMedium
A twin-engine turbojet loses one engine while cruising at FL350 over mountainous terrain where the MEA is FL190. The aircraft's single-engine service ceiling at the current weight is FL210. What should the crew do per standard drift-down procedure?
- AMaintain FL350 using maximum continuous thrust on the remaining engine
- BImmediately descend to FL190 at maximum rate of descent
- CDeclare an emergency and land at the nearest airport regardless of terrain clearance
- DDescend at the best single-engine climb speed, gradually losing altitude down toward the single-engine service ceiling while maintaining obstacle clearance
Show answer & explanationAnswer & explanation
Correct answer: D. Descend at the best single-engine climb speed, gradually losing altitude down toward the single-engine service ceiling while maintaining obstacle clearance
Drift-down is a gradual, controlled descent at the optimum single-engine speed that allows the aircraft to reach the highest altitude it can sustain on the remaining engine(s), while ensuring terrain and obstacle clearance is maintained throughout the descent.
Why the other options are wrong
- A. The aircraft cannot sustain FL350 on one engine; this would result in an uncontrolled descent.
- B. A rapid uncontrolled descent is not the correct procedure and could descend below a safe altitude too quickly.
- C. Terrain clearance must still be considered even in an emergency.
Drift-Down Procedure
A controlled descent following an engine failure at cruise altitude, flown at the optimum single-engine speed to reach the highest sustainable altitude while maintaining obstacle clearance.
- Uses best single-engine climb/descent speed
- Target altitude is single-engine service ceiling or higher of MEA
- Critical for route planning over mountainous or oceanic terrain
Memory trick: Drift down like a feather, not a rock — controlled, not panicked.