Spraying (Agricultural)

The reason for the accident with An-2 RA-84553 was performing a flight in a known defective aircraft, leading to engine failure and the need for in-flight forced landing, during which there was a collision with power lines, followed by a rough landing that led to the structural failure and fire. Investigation to determine the cause of the engine failure was not possible due to the failure to ensure the safety of the aircraft after the accident and the absence of operational and technical documentation. The adoption of the decision by the pilot to reject takeoff after detecting a loss engine power on the takeoff could have prevented the accident. The aircraft did not have a valid Certificate of Airworthiness and the time between overhauls had been exceeded on 10 April 2015.

The accident with An-2 RA-17890 aircraft was caused by its nosing-over during the emergency landing at the submerged rice bay. The emergency landing was due to the engine power loss in flight caused by the destruction of the can type combustor of the exhaust collector and burnout of the carburetor intake valve with the following high-temperature gases ingestion in the intake areas of the engine carburetor. The fatigue destruction of the can type combustor of the exhaust collector was caused along the main crack near the intake flex socket, it started from the surface of the damaged inlet port under the tube attachment pin towards the exhaust collector. By the moment of the main crack formation both inlet ports in left can type combustor under the tube attachment pin towards the exhaust collector had intolerable damage and size. During the last overhaul of the engine exhaust system of An-2 RA-17890 aircraft the left can type combustor had intolerable damage in its attaching lug to the exhaust collector which wasn't eliminated. The destruction of the inlet port valve was caused by the fusion of the boundaries of it material grains in conditions of acute temperature exposure induced by the destruction of the left can type combustor wall towards the main crack. Inadequate material (aluminum alloy D-16) of the valve specified by the drawing of aluminum allow AL-9T contributed to the valve destruction.

A loss of engine power caused by the failure of the valve on cylinder n°9 that remained in open position due to an excessive deposit of calamine (soot).

The accident was caused by the combination of the following factors:
- Violation by the crew of the airplane flight control of the An-2,
- Loss of speed while making a turn,
- Unsatisfactory knowledge of the work area by the crew.

The accident was the result of a turn at low altitude and insufficient speed under the circumstances. The following contributing factors were identified:
- High ambient temperatures,
- The static load on the airplane at its maximum permissible level,
- Dust filter switched on unnecessarily,
- Unjustified use of carburetor heating,
- Increase propeller angle in the given flight position,
- Reducing engine power in the given flight position by taking back the throttle.

In violation of Section 5.1.15 of the Guidelines for Aviation Chemical Works (ACW), the Aircrew Commander (AC) decided to combine the production flight with followed inspection of the new site, taking a representative of the Customer on board. In violation of Section 5, PPLS, the passenger was seating in the co-pilot seat and this is prohibited. Before making a decision to operate a flight, the Aircrew Commander received an indicative weather forecast from the hydro meteorology experts of Osh International Airport. The revised weather forecast was not drawn up and the crew did not receive it because the flight control officer did not send an actual weather data provided by the crew after take-off, in accordance with the requirements of paragraph 8.7.7, APKR-3 . The technology of air traffic controllers’ work at Osh International Airport does not include responsibility for the transfer of information about the actual weather obtained from the crews to base aerodrome meteorological office responsible for forecasting weather and it does not specifically define the actions of air traffic services in obtaining information about an aviation accident. No changes were made in the temperature regime when performing aviation chemical works in accordance with the Guidelines for the Implementation of ACW technology in Agriculture and Forestry” designed by the Civil Aviation Ministry, USSR, and issued on December 30, 1980, Number 668/Y (these instructions were entered into operation by the order of the Director of the Civil Aviation Department under the Kyrgyz Ministry of Transport and Communications on March 20, 2009, number 188/p in the “List of Legislative Acts Regulating the Civil Aviation Activities of the Kyrgyz Republic”). Portable emergency radio beacon, PARM -406, did not function at the time of the accident. The Statute of Aeronautical Search and Rescue Service of the Kyrgyz Republic has no changes related to its reorganization in 2007.

The accident occurred during crop-dusting flight due to late aircraft entry into climb for flying over PTL resulted in aircraft collision with power transmission line tower on a field under cultivation, followed by ground impact and fire. Probably late aircraft entry into climb was caused by PIC performance impairment (final crop dusting in final flight was performed after which PIC had to rest during 1,5 hours and short recreation cycle was disordered during flight operation), and also low-observability of PTL wires without day marking.