Feet AGL KIAS Height/Velocity Diagram 700 650 600 550 500 450 400 350 300 250 200 150 100 50 0  0 10 20 30 40 50 60 70 80 90 100 110 120 130 Avoid operation in shaded areas 10 8500 FT Density Altitude at 2500 LB Sea Level at 2500 LB Recommended Takeoff Profile Figure 7-1.  Sample height/velocity diagram for a Robinson Model  R44 II. As the airspeed increases without an increase in height, there  comes a point at which the pilot’s reaction time would be  insufficient to react with a flare in time to prevent a high  speed, and thus probably fatal, ground impact. Another thing  to consider is the length of the tailboom and the response  time of the helicopter flight controls at slow airspeeds and  low altitudes. Even small increases in height give the pilot  much greater time to react; therefore, the bottom right part of  the H/V diagram is usually a shallow gradient. If airspeed is  above ideal autorotation speed, the pilot’s instinct is usually  to flare to convert speed to height and increase rotor rpm  through coning, which also immediately gets them out of the  dead man’s curve. Conversely, an increase in height without a corresponding  increase in airspeed puts the aircraft above a survivable  uncushioned impact height, and eventually above a height  where rotor inertia can be converted to sufficient lift to enable  a survivable landing. This occurs abruptly with airspeeds  much below the ideal autorotative speed (typically 40–80  knots). The pilot must have enough time to accelerate to  autorotation speed in order to autorotate successfully; this  directly relates to a requirement for height. Above a certain  height the pilot can achieve autorotation speed even from a  zero knot start, thus putting high OGE hovers outside the  curve. cruise, without entering the shaded areas or with minimum  exposure to shaded areas. The typical safe takeoff profile involves initiation of forward  flight from a 2–3 feet landing gear height, only gaining  altitude as the helicopter accelerates through translational  lift, as airspeed approaches a safe autorotative speed. At this  point, some of the increased thrust available may be used to  attain safe climb airspeed, which will keep the helicopter out  of the shaded or hatched areas of the H/V diagram. Although  helicopters are not restricted from conducting maneuvers  that will place them in the shaded area of the H/V diagram,  it is important for pilots to understand that operation in  those shaded areas exposes pilot, aircraft, and passengers to  a certain hazard should the engine or driveline malfunction.  The pilot should always evaluate the risk of the maneuver  versus the operational value.  The grey portion on the left side of the diagram marks a flight  profile that probably does not allow the pilot to complete an  autorotation successfully, primarily due to having insufficient  airspeed to enter an autorotative profile in time to avoid  a crash. The shaded area on the lower right is dangerous  due to the airspeed and proximity to the ground resulting  in dramatically reduced reaction time for the pilot in the  case of mechanical failure, or other in-flight emergencies.  This shaded area at the lower right is not portrayed in H/V  diagrams for multiengine helicopters capable of safely  hovering and flying with a single engine failure. The following examples further illustrate the relevance of  the H/V diagram to a single-engine helicopter. At low heights with low airspeed, such as a hover taxi, the  pilot can simply use the kinetic energy from the rotor disk  to cushion the landing with collective, converting rotational  inertia to lift. The aircraft is in a safe part of the H/V diagram.  At the extreme end of the scale (e.g., a three-foot hover  taxi at walking pace) even a complete failure to recognize  the power loss resulting in an uncushioned landing would  probably be survivable. The height/velocity diagram  [Figure 7-1]  depicts altitude and  airspeed 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 is valid only when the helicopter is  operated in accordance with the gross weight versus density  altitude chart. If published, this chart is found in the RFM  for the particular helicopter.  [Figure 7-2]  The gross weight  7-3 The Effect of Weight Versus Density Altitude