A phenomenon called “Augmented Dutch Roll” during a high speed dive test caused the fatal crash of AW609 tiltrotor aircraft on October 2015...
A phenomenon called “Augmented Dutch Roll” during a high speed dive test caused the fatal crash of AW609 tiltrotor aircraft on October 2015, according to the interim investigation report released by Italian civil aviation safety investigation authority ANSV.
The second prototype with registration N609AG crashed to a field near the city of Tronzano Vercellese, Italy, killing the both experienced test pilots onboard.
Analysis of the combined CVR and FDR data, along with the telemetry data showed that the Pilot In Command (PIC) felt the onset of oscillations on the roll axis of the aircraft. He then tried to counteract that motion by maneuvering the aircraft on the roll axis, which is correct according to the normal flying technique.
However the flight control laws of the aircraft was designed to generate a coupling in the yaw axis to compensate for expected aerodynamic effect of flaperon control surface motion on yaw axis, thus forming a phenonmenon called “augmented dutch roll”.
Analysis of previous flight test data of the two flight test prototypes showed both aircraft have experienced these oscillations in roll and yaw axis, but to a lesser extend.
Also this was the first flight with the new rear fuselage configuration and tail fin modifications, to reach the maximum dive speed of 293 kt required for the certification. Earlier flight had only achieved 285 kt in dive.
During the accident flight two dives to the maximum speed of 293 kt were executed and the crash happened while executing the third one.
The investigation found that the aircraft behavior at high speed was not completely known to the manufacturer Leonardo Helicopters ( formerly AgustaWestland), also the project simulator SimRX used for developing the aircraft flight control laws, was unable to reproduce the flight profile happened in the accident flight.
ANSV recommends to review the control laws of the aircraft in the extreme flight conditions in the framework of the certification process led by US Federal Aviation Administration.
The Multi Purpose Flight Recorder (combined CVR and FDR) was significantly damaged with considerable no of parameters not recorded including latitude, longitude, ground speed, drift angle etc. Hence reconstruction of the flight during the investigation was completed using the telemetry data and MPFR data.
The AW609 tiltrotor is the first commercial tiltrotor aircraft design and combines the speed of a turboprop aircraft with the mobility of a helicopter. The aircraft takes off and land like a helicopter with its two turboshaft engines in vertical position, which then rotate to horizontal position for cruise flight. With a Maximum Take Off Weight of 7600 kg, the AW609 can seat 9 passengers.
The second prototype with registration N609AG crashed to a field near the city of Tronzano Vercellese, Italy, killing the both experienced test pilots onboard.
Analysis of the combined CVR and FDR data, along with the telemetry data showed that the Pilot In Command (PIC) felt the onset of oscillations on the roll axis of the aircraft. He then tried to counteract that motion by maneuvering the aircraft on the roll axis, which is correct according to the normal flying technique.
However the flight control laws of the aircraft was designed to generate a coupling in the yaw axis to compensate for expected aerodynamic effect of flaperon control surface motion on yaw axis, thus forming a phenonmenon called “augmented dutch roll”.
Analysis of previous flight test data of the two flight test prototypes showed both aircraft have experienced these oscillations in roll and yaw axis, but to a lesser extend.
Also this was the first flight with the new rear fuselage configuration and tail fin modifications, to reach the maximum dive speed of 293 kt required for the certification. Earlier flight had only achieved 285 kt in dive.
During the accident flight two dives to the maximum speed of 293 kt were executed and the crash happened while executing the third one.
The investigation found that the aircraft behavior at high speed was not completely known to the manufacturer Leonardo Helicopters ( formerly AgustaWestland), also the project simulator SimRX used for developing the aircraft flight control laws, was unable to reproduce the flight profile happened in the accident flight.
ANSV recommends to review the control laws of the aircraft in the extreme flight conditions in the framework of the certification process led by US Federal Aviation Administration.
The Multi Purpose Flight Recorder (combined CVR and FDR) was significantly damaged with considerable no of parameters not recorded including latitude, longitude, ground speed, drift angle etc. Hence reconstruction of the flight during the investigation was completed using the telemetry data and MPFR data.
The AW609 tiltrotor is the first commercial tiltrotor aircraft design and combines the speed of a turboprop aircraft with the mobility of a helicopter. The aircraft takes off and land like a helicopter with its two turboshaft engines in vertical position, which then rotate to horizontal position for cruise flight. With a Maximum Take Off Weight of 7600 kg, the AW609 can seat 9 passengers.
