airspeed increases beyond that which gives minimum rate of descent, the rate of descent increases again.  Today helicopters are quite reliable. However  emergencies do occur, whether a result of mechanical failure or pilot error. By having a thorough knowledge of the helicopter and its systems, you will be able to more readily handle the situation. In addition, by knowing the conditions that can lead to an  emergency, many potential accidents can be avoided. When landing from an autorotation, the energy stored in the rotating blades is used to decrease the rate of descent and make a soft landing. A greater amount of rotor energy is required to stop a helicopter with a high rate of descent than is required to stop a helicopter that is descending more slowly. Therefore, autorotative descents at very low or very high airspeeds are more critical than those performed at the minimum rate of descent airspeed. In a helicopter, an autorotation is a descending maneu- ver where the engine is disengaged from the main rotor system and the rotor blades are driven solely by the upward flow of air through the rotor. In other words, the engine is no longer supplying power to the main rotor. Each type of helicopter has a specific airspeed at which a power-off glide is most efficient. The best airspeed is the one which combines the greatest glide range with the slowest rate of descent. The specific airspeed is somewhat different for each type of helicopter, yet  certain factors affect all configurations in the same manner. For specific autorotation airspeeds for a partic- ular helicopter, refer to the FAA-approved rotorcraft flight manual. The most common reason for an autorotation is an engine failure, but autorotations can also be performed in the event of a complete tail rotor failure, since there is virtually no torque produced in an autorotation. If altitude permits, they can also be used to recover from settling with power. If the engine fails, the freewheel- ing unit automatically disengages the engine from the main rotor allowing the main rotor to rotate freely. Essentially, the freewheeling unit disengages anytime the engine r.p.m. is less than the rotor r.p.m. The specific airspeed for autorotations is established for each type of helicopter on the basis of average weather and wind conditions and normal loading. When the helicopter is operated with heavy loads in high density altitude or gusty wind conditions, best  performance is achieved from a slightly increased air- speed in the descent. For autorotations at low density altitude and light loading, best performance is achieved from a slight decrease in normal airspeed. Following this general procedure of fitting airspeed to existing conditions, you can achieve approximately the same glide angle in any set of circumstances and estimate the touchdown point. At the instant of engine failure, the main rotor blades are producing lift and thrust from their angle of attack and velocity. By immediately lowering collective pitch, which must be done in case of an engine failure, lift and drag are reduced, and the helicopter begins an immedi- ate descent, thus producing an upward flow of air through the rotor system. This upward flow of air through the rotor provides sufficient thrust to maintain rotor r.p.m. throughout the descent. Since the tail rotor is driven by the main rotor transmission during autoro- tation, heading control is maintained as in normal flight. When making turns during an autorotation, generally use cyclic control only. Use of antitorque pedals to assist or speed the turn causes loss of airspeed and downward pitching of the nose. When an autorotation is initiated, sufficient antitorque pedal pressure should be used to maintain straight flight and prevent yawing. This pressure should not be changed to assist the turn. Use collective pitch control to manage rotor r.p.m. If rotor r.p.m. builds too high during an autorotation, raise the collective sufficiently to decrease r.p.m. back to the Several factors affect the rate of descent in autorota- tion; density altitude, gross weight, rotor r.p.m., and airspeed. Your primary control of the rate of descent is airspeed. Higher or lower airspeeds are obtained with the cyclic pitch control just as in normal flight.  In theory, you have a choice in the angle of descent varying from a vertical descent to maximum range, which is the minimum angle of descent. Rate of descent is high at zero airspeed and decreases to a minimum at approximately 50 to 60 knots, depending upon the par- ticular helicopter and the factors just mentioned. As the 11-1 AUTOROTATION