AgustaWestland announced late last month that its AW609 Tiltrotor has completed dual-engine failure autorotation tests. This is a big milestone in the long development process that will result in the world’s only civilian tiltrotor, planned for certification in 2017.
The aircraft’s massive prop rotors make it impossible to land and take off with the engines in airplane mode. Because the aircraft exists in the space somewhere between an airplane and a helicopter, AW had to work with the FAA to determine exactly how it would be tested. The result was a requirement to be able to land safely in the same way a helicopter does after a failure in either mode. For the testing program that meant a demonstrated ability to go from a worst case scenario of full aircraft mode to a safe landing in full helicopter mode.
The few people outside company test pilots who have flown the aircraft praise its automated systems management capability. That is on display during the autorotation, where the aircraft automatically maintains an angle of incidence that results in 100 percent rpm after an engine or drive system failure. As the aircraft descends it must at some point convert fully to helicopter mode, which the company said it does rapidly. The nacelles go to a full aft position of 95 degrees for a run-on landing.
Most interesting about the aircraft is what might lead to a failure. It’s powered by Pratt & Whitney PT6 engines, each with its own gearbox. Both are connected by a common drive shaft, so if one engine fails the other working engine will provide power to both. AW thinks a complete and simultaneous dual failure is highly improbable, and the only time they envision a subsequent failure is with fuel contamination. Either way, more than 70 tests over 10 flight hours appears to prove the aircraft has the ability to handle such a problem.