Gazpromavia Superjet Crash Caused By Malfunctioning AOA Sensor

An investigation by the Moscow-based Interstate Aviation Committee has concluded that a malfunctioning angle-of-attack (AOA) sensor played a central role in the crash of a Gazpromavia Superjet 100 regional jet on July 12.

The aircraft, which carried reg. RA-89049, went down during a ferry flight back to Moscow Vnukovo International Airport from a maintenance center at Lukhovitsy, outside Moscow, where it had passed 2А, 4А, 1C, 2С and 5С checks.

According to the investigator’s report, the first sudden changes in the AOA values were recorded during the takeoff roll after the SSJ100 reached a speed of 60 kt. at a pitch angle of 0 deg. A speed discrepancy was indicated 2 min. after takeoff when the flaps had been retracted.

Two minutes later, the pilots attempted to climb, but the stabilizer began to trim nose-down, and the aircraft started to descend. At that point, the pilots realized that the AOA sensors were not working properly, but the AOA limit system did not allow the crew to pull up. The elevator had been deflected for nose-down due to the presence of AOA feedback signals in the control system and to compensate for the nose-up movement caused by the deployment of the spoilers.

The aircraft crashed 6 min. after takeoff in a forest near Kolomna at a speed of 365 kt. and at a pitch angle of 25 deg. nose-down. The two pilots and one flight attendant onboard died in the crash.

The investigation revealed that two out of four AOA sensors on the aircraft were replaced during the C check in Lukhovitsy. These sensors provided data for the captain’s and the second pilot’s primary flight displays. The two intact sensors provided data for the reserve air data computer.

Another Gazpromavia’s SSJ100—reg. RA-89029—experienced similar discrepancies in AOA and speed readings during a ferry flight on May 6 after it also had two AOA sensors replaced during maintenance at Lukhovitsy. At that time, the crew switched the captain’s instruments to the reserve air data computer and successfully completed the flight, the report said.

The SSJ100’s manufacturer, Yakovlev, informed investigators that it had begun developing a service bulletin to clearly secure the AOA sensor mounting plate to a specific location on the aircraft by applying corresponding permanent markings to the surface of the plate.

Additionally, the company is preparing a bulletin for pilots regarding the operation of the AOA limit system in the event of incorrect data from two or more automatic dependent surveillance channels.