Plain English Meaning

When a helicopter loses engine power, the rotor blades keep spinning on their own because air flows up through them as the helicopter descends. The pilot uses this spinning to glide down and land safely.

Full Definition

A flight condition in a helicopter where the main rotor system is driven by air flowing up through the rotor disc rather than by engine power. It is used as an emergency procedure following an engine failure, allowing the pilot to make a controlled descent and landing without engine power.

Context Anchor

Seen in helicopter emergency procedures, especially engine-failure training and without engine power.