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] 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. 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 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.  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. 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 The height/velocity diagram depicts altitude and air- speed situations from which a successful autorotation 11-5 THE EFFECT OF WEIGHT VERSUS DENSITY ALTITUDE VORTEX RING STATE (SETTLING WITH POWER) Figure 11-3. Assuming a density altitude of 5,500 feet, the height/velocity diagram in figure 11-2 would be valid up to a gross weight of approximately 1,700 pounds. This is found by entering the graph at a density altitude of 5,500 feet (point A), then moving horizontally to the solid line (point B). Moving ver- tically to the bottom of the graph (point C), you find that with the existing density altitude, the maximum gross weight under which the height/velocity diagram is applicable is 1,700 pounds. Figure 11-2. By carefully studying the height/velocity  diagram, you will be able to avoid the combinations of alti- tude and airspeed that may not allow you sufficient time or altitude to enter a stabilized autorotative descent. You might want to refer to this diagram during the remainder of the  discussion on the height/velocity diagram. A B C 7,000GLYPH<.notdef> 6,000GLYPH<.notdef> 5,000GLYPH<.notdef> 4,000GLYPH<.notdef> 3,000 1,500 1,600 1,700 1,800 1,900 GROSS WEIGHT – POUNDS DENSITY ALTITUDE –FEET 500GLYPH<.notdef> 450GLYPH<.notdef> 400GLYPH<.notdef> 350GLYPH<.notdef> 300GLYPH<.notdef> 250GLYPH<.notdef> 200GLYPH<.notdef> 150GLYPH<.notdef> 100GLYPH<.notdef> 50GLYPH<.notdef> 0 A B Smooth Hard Surface .GLYPH<.notdef> Avoid Operation inGLYPH<.notdef> Shaded Areas. INDICATED AIRSPEED KNOTSGLYPH<.notdef> (CORRECTED FOR INSTRUMENT ERROR) HEIGH T ABOVE SURFACE - FEET 0 10 20 30 40 50 60 70 80 90 100 110 120 