Following the Pulkovo Airlines Ilyushin Il-86 crash, inspectors of Russia's State Service of Civil Aviation (GSGA) are continuing checks on the Il-86 fleet, but these have so far shown no horizontal stabiliser control problems. A stabiliser pitch-up just after take-off from Moscow Sheremetyevo, caused the 28 July crash, but why it happened is not known.
The GSGA admits that the cause may never be clear because the cockpit voice recorder (CVR) has no useful material on it and the stabiliser trim selectors were destroyed. Of the 103 Il-86s produced, 40 airframes remain in airline service.
Aleksandr Emtsov, deputy chief of the GSGA flight safety department, says the flight data recorder shows that "two seconds after take-off the stabiliser started moving to higher pitch and soon reached the +12° mechanical limit…but we do not know why it did so."
All four horizontal stabiliser actuators were working. The director of Russia's state centre for air transport flight safety, Henry Livshits, says: "This means a command signal was fed to these actuators. Aerodynamic forces could not produce that effect." The pilots were trying to compensate by using the elevator, but, he explains, "it can only compensate for 5° stabiliser pitch-up".
Emtsov says "nothing like this has been observed on the Il-86". The stabiliser control unit on the Il-86's yoke has two identical switches. The pilot needs to push both to move the stabiliser. In the Pulkovo case, both control switches needed to be stuck or pushed by the pilot's thumbs to have this effect. "We have all the evidence that 14min before take-off the checks had been performed in full, with no warning of anything abnormal."
Source: Flight International