DAVID LEARMOUNT / LONDON
Investigation shows impact of DHL Boeing 757 tail on port fuselage of Tupolev Tu-154 brought down aircraft
The German accident investigation agency (BFU) has revealed the two airliners which collided over southern Germany on 1 July were brought down by the impact of the Boeing 757's tail on the fuselage of the Tupolev Tu-154M as the 757 passed underneath it.
Wreckage and flight data analysis shows that when the aircraft collided the Bashkirian Airlines Tu-154M was heading west on 274°, the DHL 757-200F north on 004°, both at flight level (FL) 360 (36,000ft/11,000m) and it was the impact of the 757's tail on the port fuselage of the Tu-154 near its emergency exits that precipitated the break-up of the Tu-154 and the 757's loss of control.
The aircraft's data recorder timelines and the air traffic control (ATC) tapes reveal the Tu-154M pilots obeyed within 7s an ATC call to carry out an expedited descent to FL 350, but did not acknowledge it until it was repeated 14s later. As the crew was descending, they received a climb order from their airborne collision avoidance system (ACAS). The crew decided to continue descent, and the repeated ATC descent instruction 7s later may have served to confirm their decision. They ignored the ACAS "resolution advisory" (RA) and also another RA 28s later calling for the crew to "increase climb".
The 757 crew, however, had immediately followed their RA requiring descent, told ATC of their action, and the two aircraft were set on collision trajectories. The BFU report says: "From the flight recorders it is evident crew members of both aircraft became aware of the proximity of the other aircraft several seconds before the collision and tried to prevent it by appropriate flight manoeuvres."
The report confirms the aircraft were fitted with Honeywell 2000 traffic alert and collision avoidance systems version 7, both serviceable, which gave their complementary traffic advice and RAs to the two crews at the same time. There was no indication of any malfunctions in either aircraft.
ACAS gives RA "increase climb"
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Collision
Collision
Source: Flight International
