International investigators led by Italy's national flight safety agency are wrapping up their probe of the October 2015 in-flight breakup of AW609 prototype that killed its two test pilots and interrupted final development and certification of that civil tiltrotor.
The Agenzia Nazionale per la Sicurezza del Volo (ANSV)-led investigation has been scrutinizing the interaction of the AW609’s fly-by-wire flight control system and the pilots during final flight-test sequence. The Italian agency's work includes an assessment of any aircraft-pilot coupling in which out-of-phase control inputs by the flight crew or responses by the flight control system may have inadvertently sustained aircraft oscillations and pitch, roll, yaw and airspeed (or combination of those factors).
Investigators reportedly are not considering that the pilots’ actions started the accident sequence, but that their interactions with the AW609’s flight control system might have intensified or prolonged the sequence that led to the in-flight breakup.
As part of their work, the investigators reviewed an incident that occurred some months in which an AW609 flight test in Italy was terminated after one of the rotors struck a wing leading edge, resulting in an emergency landing.
The Oct. 30, 2015, breakup led to a suspension of flight tests that ended Jan. 30 when the No. 3 prototype took flight from Leonardo's Philadelphia facility. The manufacturer now aims to achieve certification of the tiltrotor in 2018; it had targeted that for this year before the crash.
The ANSV convened representatives of the international team in early April to review their findings and discuss the awarding of their conclusions and recommendations in the final report on the probe. The investigative team includes representatives of AW609 manufacturer Leonardo Helicopters, Pratt & Whitney Canada (which makes the aircraft's PT6C engines), Bell Helicopter (which launched development of tiltrotor with then-Agusta Aerospace), the U.S. FAA and National Transportation Safety Board.
The crash occurred Oct. 30, 2015, while AW609 Prototype No. 2 (bearing the registration N609AG) was performing a high-speed flight test. About 27 minutes into that test, real-time telemetry from the aircraft was lost, according to Leonardo, which added that there was no further contact. The manufacturer said tests scheduled for that day included high-speed ones that “had already successfully been performed” by the No. 1 prototype.
Wreckage of the civil tiltrotor was found in the small town of Santhià, about 30 nm west-southwest of the aircraft’s departure point, AgustaWestland’s base at Cascina Costa di Samarate.
In a related development, a criminal prosecutor in the region reportedly has received final report from aviation advisors on their assessment of the crash’s causes. The prosecutor is tasked with assessing culpability in the deaths of the two pilots.