Pilots Discuss Use of Osprey

We have not seen a vortex ring state event in the fleet. Other than the mishap, the only other time this has been seen was during the extensive testing where were actually looking for it -- to gather the data during test flights. From that testing we learned that MV-22 is less susceptible to VRS than any other military rotorcraft currently in use (i.e. it's harder to get MV-22 into VRS than a regular helicopter). We also implemented a warning system that tells the pilot when they are approaching the boundary, and we learned that just tilting the nacelles forward a couple of degrees, which is just a flick of your thumb, alleviates the condition nearly instantly.

It is a fairly narrow condition of slow speed and high rate of descent. However, it should be in the range of foreseeable use of the aircraft. It is not so much that the Osprey can get into [vortex ring state], it is how it responds. Even conventional helicopters can get into VRS. What the Osprey does different is its aerodynamic reaction. In a conventional helicopter, the thrust (and effect of VRS) is centered on the fuselage. To recover from VRS in a conventional helicopter, the pilot reduces power and adds forward stick (pitches forward). The conventional helicopter will fly itself out of it. In the V-22, the two rotors are set at the ends of the wing tips. If the helicopter encounters VRS, it is likely that it will occur asymmetrically, i.e. affecting one rotor more than the other. If this occurs the dissymmetry of lift of the two rotor systems will cause the V-22 to roll. Because of the immense thrust of the engines and the weight of the engines, pylons and rotor systems, the roll rate can become so rapid that a pilot cannot recover if in a landing mode. Instead of naturally pitching forward like a conventional helicopter would do and fly out of VRS, the VRS rolls inverted and dives into the ground. This is part of what happened on April 7, 2000 killing 19 Marines.

VRS is not the only thing that can cause the Osprey to enter an unrecoverable roll. Any malfunction in flight controls, flight computer, or hydraulics that creates an asymmetrical condition on the Osprey can create a roll that can be unrecoverable. In addition, aerodynamic conditions such as uneven airflow around a superstructure of a ship, mountain wave conditions or the wake from other aircraft can also induce an asymmetrical condition. Environmental factors can contribute as well including uneven icing conditions or battle damage.