"Dead man's curve" is a danger zone for helicopters where flying too low and too slow can make it nearly impossible to land safely if the engine fails.
This area is shown in a helicopter's height-velocity (HV) diagram, which helps pilots know what combinations of height and speed to avoid. If a helicopter is too close to the ground and moving slowly, it may not have enough time or energy to land safely in an emergency.
Pilots stay out of this zone by keeping enough height or speed, especially during risky maneuvers like takeoff and landing.
