Helicopter height–velocity diagram

The FAA states "The height–velocity diagram or H/V curve is a graph charting the safe/unsafe flight profiles relevant to a specific helicopter.

As operation outside the safe area of the chart can be fatal in the event of a power or transmission failure it is sometimes referred to as the dead man's curve.

[2] The H/V curve is a diagram indicating the combinations of height above ground and airspeed that should be avoided due to safety concerns relating to emergency landings.

Conversely, a complete power loss, and resultant crash landing, from a three-foot hover taxi at walking pace may be survivable.

If above ideal autorotation speed, a pilot can avoid the deadman's curve by flaring, converting airspeed into height, and increasing rotor RPM through coning.

Bell 204B height–velocity diagram, showing the unsafe region on the left, due to insufficient airspeed for autorotation, the takeoff profile, and the unsafe region on the lower right due to limited pilot reaction time. [ 1 ]