Plain, Valley

The aircraft accident was caused by a sudden loss of control of the aircraft in clouds while turning in for the approach to Friedrichshafen at night. Probably the frontal weather with light to moderate turbulence, snowfall and icing contributed to this. The absence of information about the events on board the aircraft meant that it was not possible to determine the causes of the loss of control.

Double engine failure in flight due to fuel starvation, forcing the crew to attempt an emergency landing in trees.
The following contributing factors were identified:
- Recurrent failures on the ground and in flight of the aircraft fuel quantity indicators, a situation that was maintained because the Maintenance Programme did not include an inspection and calibration of the fuel quantity gauges.
- Initiating the flight with a fuel indication system inoperative.
- Complacency on part of the crew who decided to continue the flight by having an aerodrome nearby after the first engine failure.

The probable cause of the accident was the shut down of the right engine and then the left engine, possibly due to a faulty shut down on part of the crew. In the course of the subsequent emergency descent due to complete loss of power of the engines with no radio communication with air traffic controllers, as well as possibly due to the resulting confusion and nervousness, the crew unintentionally forgot to switch the pressure value on the mechanical barometric altimeter of the aircraft to the pressure on the landing airfield (704 mm Hg), leaving the pressure value of 760 mm Hg, which led to incorrect readings of true altitude of the flight. Subsequently, the crew was able to start the engines and attempt to make a forced landing at a distance of 28 km from the airfield of Almaty at night in poor weather conditions in an unlit area. Incorrect readings on the barometric altimeter of the true flight altitude (the radio altimeter showed 750 m) resulted in the aircraft colliding with a power line, causing a fire, as well as colliding with the ground, as a result of which the aircraft structure completely collapsed and burned down.

The cause of the accident was an inner mechanical defect in the left engine past its stipulated TSO. The defect caused a forced stall of the engine. For this reason, the propeller on this engine could not be feathered. During the shutdown of the right engine, the feathering of the propeller on this engine did not take place. The aircraft entered to the fall and a stall-spin in which it fell to the ground.
Contributing factors:
- The left engine TSO was over the stipulated limit of 12 years. (The last general overhaul was performed on 29 October 2001.),
- Limited experience of the pilot on this type of aircraft.

Loss of engine power due to the failure of the cylinder n°5 caused by a faulty manufacturing.

Loss of control during climb due to the combination of the following factors:
- The particular characteristics of the aircraft;
- The attention required by the transponder as it is not displayed by air traffic control;
- The detour of the planned flight at the request of the inspection department of air traffic;
- Aircraft trajectory management with autopilot switched off;
- The pilot's limited experience in instrument flight conditions. In addition, the absence of additional instruction in the aircraft type (due to the lack of specific regulations) can be considered a contributing factor, according to the probable scenario described above. In addition, the research identified the following elements with potential impact in operational safety:
- Absence of the TAWS system on the aircraft in non-conformity with the established RAAC 91;
- Lack of effective means to enable the flight plan office to quickly determine whether an aircraft has operating restrictions;
- Shortcomings in the training of staff in the units ATS and SAR in search and rescue.