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You should avoid the low altitude, high airspeed portion of the diagram (section B), because your recognition of an engine failure will most likely coincide with, or shortly occur after, ground contact. Even if you detect an engine failure, there may not be sufficient time to rotate the helicopter from a nose low, high airspeed attitude to one suitable for slowing, then landing. Additionally, the altitude loss that occurs during recognition of engine fail- ure and rotation to a landing attitude, may not leave enough altitude to prevent the tail skid from hitting the ground during the landing maneuver. 

Basically, if the helicopter represented by this H/V dia- gram is above 445 feet AGL, you have enough time and altitude to enter a steady state autorotation, regardless of your airspeed. If the helicopter is hovering at 5 feet AGL (or less) in normal conditions and the engine fails, a safe hovering autorotation can be made. Between approximately 5 feet and 445 feet AGL, however, the transition to autorotation depends on the altitude and airspeed of the helicopter. Therefore, you should always be familiar with the height/velocity diagram for the particular model of helicopter you are flying. 

## THE EFFECT OF WEIGHT VERSUS DENSITY ALTITUDE 

The height/velocity diagram depicts altitude and air- speed situations from which a successful autorotation 

can be made. The time required, and therefore, altitude necessary to attain a steady state autorotative descent, is dependent on the weight of the helicopter and the density altitude. For this reason, the H/V diagram for some helicopter models is valid only when the helicop- ter is operated in accordance with the gross weight vs. density altitude chart. Where appropriate, this chart is found in the rotorcraft flight manual for the particular helicopter. [Figure 11-3] 

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The gross weight vs. density altitude chart is not intended as a restriction to gross weight, but as an advi- sory to the autorotative capability of the helicopter during takeoff and climb. You must realize, however, that at gross weights above those recommended by the gross weight vs. density altitude chart, the H/V diagram is not restrictive enough. 

## VORTEX RING STATE (SETTLING WITH POWER) 

Vortex ring state describes an aerodynamic condition where a helicopter may be in a vertical descent with up to maximum power applied, and little or no cyclic authority. The term the fact that helicopter keeps settling even though full engine power is applied. 

In a normal out-of-ground-effect hover, the helicopter is able to remain stationary by propelling a large mass of air down through the main rotor. Some of the air is recirculated near the tips of the blades, curling up from the bottom of the rotor system and rejoining the air 

