The aircraft, registered RA-85572, crashed soon after taking off from Sochi, where it had stopped to refuel. Built in 1983, it was carrying the Alexandrov military choir and orchestra to perform for Russian forces serving in Syria. It had accumulated 6,689 flight hours, spending its entire service life with the Russian air force, including with the 223 Flight Detachment of the Russian defense ministry. It underwent heavy maintenance two years earlier and was serviced two months before the crash.
On December 26 and 27, divers were able to locate and recover the aircraft’s voice and flight data recorders, both of which were found in a good condition. The data retrieved thus far indicates that the flap-setting mechanism worked incorrectly in climb. Further, the crew seemed to be unable to take corrective action to address the problem in flight. The flight recorder also revealed that in moments before crash the commander recognized the failure, as he used the word “flaps” when talking to other crew members. Analysis of the retrieved data continues, and more findings are expected to be made public by year-end.
Investigators say their findings are preliminary, and the Russian defense ministry promised to publish a full report once the investigation is complete. The work is led by the Russian defense ministry’s central air force scientific research institute in Lyubertsy near Moscow.
It was not yet possible to assess whether the crew’s actions were in full compliance with regulatory requirements in the event of a flap failure. The Tu-154B-2 flight manual requires the crew to retract the flaps in two stages, pulling them in completely at the speed of 360 km/h. There was also no information made public on the distribution of loads inside the airplane and its center of gravity position, important considerations for a tri-jet with rear-positioned engines. There was speculation that the aircraft might have flown into a flock of birds, which led to a technical failure. Investigators expect that all three Nikolai Kuznetsov NK-8 engines will be recovered from the sea bottom for inspection.
The investigators are also viewing videos taken by people who witnessed the aircraft’s takeoff and climb-out. The tri-jet was last seen executing a right turn at the speed of 500 to 550 km/h. On December 29, investigators said the Tu-154B-2 was in the air for 70 seconds and attained a maximum altitude of 150 meters (492 feet).
An SPZ-1A sensor device is used to monitor whether the flaps move symmetrically; if they do not, it de-activates the hydraulic actuator and issues a warning to the crew to assume manual control. The Tu-154B-2 flight manual and other documents prescribe using an electrically-controlled stabilizer and control yoke to offset the diving force that the flaps generate should they have not retracted. Crews are required to perform simulator training to deal with such a situation. If the failure of the flaps retraction mechanism is discovered in a timely manner, the pilots are instructed to land at the nearest airfield while maintaining a relatively low speed. They are also instructed to keep the throttles at a low setting so that the engine thrust does not further complicate the issue of aircraft stability and controllability.
Developed in the early 1960s, the Tu-154 first flew in 1966 and entered production between 1968 and 1970. More than 600 copies were built before the manufacturing plant changed in 1984 for more advanced Tu-154M. Total production reached 930 aircraft, with the last example completed in February 2013 for the Russian defense ministry. Some 70 Tu-154s were lost in accidents and crashes. Several dozen Tu-154M jets remain in active service worldwide, mostly with government agencies, but some with commercial airlines.
(Vladimir Karnazov - AINOnline News)