Drift Down

Drift down is a procedure used by pilots when an engine fails at high cruising altitude. Since the aircraft can no longer maintain level flight at the original altitude with reduced power, the aircraft descends to a lower altitude where it can safely continue flying on the remaining engine(s). This descent is managed in a controlled way to ensure obstacle clearance, optimized fuel burn, and safety throughout the procedure.

Modern airliners are equipped with engine-out performance data and drift-down charts that assist pilots in determining the most suitable altitude for continued flight. These charts factor in aircraft weight, environmental conditions, and terrain along the route. The calculated drift-down path typically provides clearance from high terrain by maintaining a minimum obstacle clearance altitude (MOCA) or engine-out escape path where required.

The concept of drift down is especially important in extended twin operations (ETOPS) and transoceanic flights, where alternate airports may be hundreds of miles apart. Understanding drift-down performance helps ensure the aircraft remains within certified performance limits and is a critical component of inflight decision-making during engine failure scenarios.