The (Stealth) Blackhawk Crash
The reason a stealthy version of the MH-60 Blackhawk crashed during the May 1 raid that killed Osama bin Laden includes the vortex ring state phenomenon, according to officials, but helicopter crashes in the Middle East are far from uncommon. Hot air close to the ground and the aircraft's proximity to the high walls of the compound could have caused that thin, hot air to be driven by propwash up the walls and then down through the rotor, causing the vortex ring state. With those conditions, the helicopter would have lost lift and settled with power, which is what officials say happened. The resulting hard landing immediately altered the original plan for SEALS to fast rope to the ground from a hovering aircraft. They fared better than they might have. In Iraq, only IED explosions and being shot by the enemy rank higher than U.S. helicopters for killing American soldiers, according to the Armed Forces Journal. And 80 percent of the helicopter accidents occur without the intervention of hostile forces. That said, the military helicopter crash rate is actually better than that of GA aircraft.
The non-hostile, non-combat accident rate for military helicopters currently stands near 2.1 per 100,000 hours while flying in some of the least hospitable conditions available to helicopters. Meanwhile, the accident rate for GA aircraft stands at 6.86 per 100,000 hours. The military helicopter pilots are most often brought down due to a combination of weather conditions and terrain. Night vision goggles have improved matters, but dust storms, brownouts caused by rotor wash, wire strikes and controlled flight into terrain are still problems the military and Congress hopes to better address. Proposed fixes include terrain avoidance avionics that would warn pilots of potential hazards. That specific technology would not have helped during the bin Laden raid, for which the mission profile put the aircraft in a hover at treetop level. Three-dimensional radar, also a proposed fix, penetrates brownouts and could have produced a synthetic image of the landing zone, but may not have saved the aircraft from vortex ring state.