Incident Overview
On the day of the accident, the crew of a Tu-154M aircraft encountered technical problems while preparing for departure from Irkutsk Airport. Starting all three engines took 17 minutes due to an issue with the starter of engine number 2. A warning light activated in the cockpit, but the crew, believing it to be a false alarm, decided to proceed with the takeoff after finding no corrective actions in the operations manual.
Technical Issues and Decision
The starter on engine number 2 had a technical malfunction that manifested as a warning light during preflight. The crew considered the warning unreliable and opted to depart despite the unresolved indication. The flight departed runway 12.
Starter Failure and Fire
Four minutes after takeoff, while climbing, the starter on engine number 2 failed. Debris scattered and severed hydraulic and fuel lines. The crew declared an emergency and received clearance for an immediate return after engine number 2 caught fire. However, they were unable to extinguish the fire, and the aircraft entered an uncontrolled descent.
Crash and Casualties
The aircraft crashed on farm buildings approximately 11 kilometers from the airport. The impact disintegrated the aircraft. All 124 occupants on board were killed. One farmer on the ground was also killed, and another farmer sustained serious injuries.
Probable Cause
According to the official investigation, the starter malfunction occurred when a structural element of the air conditioning system, likely a fragment of the air-to-air radiator splitter of engine number 2, struck the constant pressure flap during engine start. This was possible due to the lack of protection against foreign objects in the air lines and low operational reliability of the radiator. A constant supply of pressurized air from the other engines, operating near nominal thrust, kept the starter engaged, causing the turbine to overspeed and triggering a 'Dangerous starter speed' alarm, which the flight engineer detected after all engines were started. Pressing the starter shutdown button did not clear the alarm. The crew, believing the alarm was false, made the wrong decision to take off, a consequence of their unpreparedness due to inadequate regulatory documentation, insufficient information support, and a lack of detailed technical condition monitoring for the starter in the cockpit. Additionally, routing the main lines of all three hydraulic systems through the fire-hazardous compartment of engine number 2 was identified as a design deficiency of the Tu-154M.