The flight departed Prague airport at 8:52 and proceeded routinely to Bratislava. At 9:35:10 the flight was cleared by Bratislava tower to land on runway 22. For reasons that are unclear, the crew executed a highly unstabilized ILSinstrument approach to runway 22, with rates of descent as high as instead of ; speeds varying from instead of ; and flap selection directly from 0 degree to full flaps instead of in gradual increments. As they approached the runway, the crew inadvertently set thrust reversal at the no. 2 and no. 3 engine while still airborne. The thrust reversal caused the no. 3 engine to fail and the crew then inadvertently feathered the no. 4 prop, losing all thrust on the right side of the aircraft. At above the runway threshold the crew attempted to execute a go around. They tried to restart the no. 4 engine at, but the ensuing right bank due to asymmetric thrust increased; the aircraft then lost control and struck lake Zlaté piesky in a 60 degree right bank and a 60 degree nose down attitude.
Investigation
The investigators published the causes as follows:
Use of thrust reversal at altitude under.
Improper manipulation of the thrust levers of the inner engines.
Reducing speed under the allowed limit on final approach.
Erroneous feathering of the engine number 4 propeller.
Failure to bank the plane towards the working engines side.
The immediate cause was the attempt to start engine number 4 at low speed and altitude.
Rescue operation
The plane crashed into a lake in a densely populated area and rescue operations started immediately after the crash. Svazarm divers tried to help, but most passengers drowned or died due to crash forces. Initially, four passengers were pulled out alive; one passenger later died in the hospital.
Controversy
A surviving passenger later claimed in an interview that flight captain requested emergency landing in Brno but it was rejected because of the Vietnamese delegation visiting the city and an emergency landing would harm the image of the country. He also claimed that Vienna airport offered an emergency landing permission but communist authorities rejected it. It is unclear how a surviving passenger would be aware of the captain's actions during the flight, or how searching for an alternate emergency landing site relates to an unstabilized approach with inadvertent thrust reversal deployment at Bratislava.
