Drift Down and Escape Routes

What is Drift Down?

Drift down is the controlled descent performed after an engine failure when the aircraft is above its one-engine-inoperative (OEI) cruise ceiling. The goal is to descend to an altitude where the remaining engine(s) can sustain level flight. The drift down procedure is calculated to ensure the aircraft clears all obstacles by a regulatory margin—typically 2000 ft within 5 NM (9.3 km) either side of the intended track during descent, and 1000 ft once stabilized at the new cruise altitude.

Drift Down Procedure

• Initiate drift down immediately after engine failure if above OEI ceiling.
• Set maximum continuous thrust (MCT) on the operative engine(s).
• Fly at the optimum drift down speed (VMD for jets, 1.1 VS for props) to maximize obstacle clearance or range, depending on the situation.
• If required for terrain clearance, fuel jettisoning should start at the beginning of the drift down, but always retain enough fuel for safe diversion and reserves.

Escape Route Planning

Escape routes are pre-determined lateral and vertical paths that guarantee obstacle clearance during drift down, especially over high terrain or remote areas. These routes are charted based on the highest obstacles within a specified corridor (usually 5 NM either side of track) and take into account aircraft performance, wind, and fuel requirements. Accurate position determination before descent is essential to ensure the escape route provides the necessary ground clearance.

Key Calculations

• Determine wind correction angles and ground speeds to ensure the aircraft remains on the intended escape route.
• Identify the highest obstacle within the defined corridor along the route.
• Calculate revised fuel and landing mass if an in-flight diversion is required, ensuring final reserve fuel is always available at the alternate.

Commander’s Responsibilities

The commander must verify that, even in the event of a diversion, the aircraft can reach a suitable aerodrome with the required fuel reserves. In-flight updates require reassessment of destination suitability, meteorological conditions, and landing mass at the alternate.