While cruising over high mountainous terrain, a twin-engine transport experiences a failure of one engine. The crew is unable to maintain the current cruise altitude on the remaining engine and initiates a drift-down procedure. What is the primary objective of this maneuver?
- ATo immediately divert to the nearest suitable airport regardless of terrain clearance
- BTo descend at a speed and configuration that optimizes single-engine climb performance while maintaining terrain and obstacle clearance until reaching a new stabilized altitude
- CTo jettison fuel first, then maintain the original cruise altitude using maximum continuous thrust
- DTo descend as rapidly as possible to minimize fuel burn on the remaining engine
Show answer & explanationAnswer & explanation
Correct answer: B. To descend at a speed and configuration that optimizes single-engine climb performance while maintaining terrain and obstacle clearance until reaching a new stabilized altitude
Drift-down is a controlled descent following an engine failure at altitude, flown at the speed for best single-engine climb performance (typically near best L/D or a specified drift-down speed) so the airplane loses altitude as slowly as possible while remaining clear of terrain and obstacles, until it stabilizes at a new single-engine cruise/ceiling altitude. It is not a rapid emergency descent, nor does it bypass terrain clearance planning.
Why the other options are wrong
- A. Diversion decisions are separate from the drift-down maneuver itself, which focuses on altitude and terrain clearance.
- C. Fuel jettison may be considered separately, but drift-down itself is about descent profile, not maintaining original altitude.
- D. Rapid descent is not the goal; the objective is to minimize altitude loss while clearing terrain.
Drift-Down Procedure
A controlled descent following an engine failure at altitude, flown at optimum single-engine climb speed to minimize altitude loss while maintaining terrain/obstacle clearance until reaching a new stabilized altitude.
- Triggered when single-engine thrust cannot maintain current altitude
- Flown at best single-engine climb/L-max speed
- Requires pre-planned escape routes over mountainous terrain
- Ends at a new single-engine cruise ceiling altitude
Memory trick: Drift down like a feather, not a rock — save altitude for terrain clearance