AN-24 RA-47302 09.07.2011

     The Interstate Aviation Committee Investigation team has completed the investigation of the accident with An-24RV RA-47302 aircraft operated by "Angara" Airlines occurred in the Tomsk region (RF) on July 11, 2011.
     The fatal accident with An-24RV RA-47302 aircraft occured during the emergency ditching caused by fire in nacelle of AI 24 2 series № Н49312005 left engine. The aircraft destruction with people fatalities was caused by aircraft collision with submurged obstacles that couldn't be predicted and prevented by the crew.
     Fire most probably was caused by pressurization of left engine breather system due to destruction of TsS-24 № G872VТ9 centrifugal breather followed by emission of air-oil emulsion in cowl compartment and late engine cut-off by crew when the chip warning was actuated as well, PCM pressure variation of left engine within the fame of ± 5 kg/cm², burning odor and oil pressure drop below alowable value.
     Untimely pilot information on the engine elevated vibration due to deterioration of ИВ 41AM vibration measurement system performance most probably due to rotor speed cycling during destruction of compressor rotor rear support structure bearing and (or) maladjustment of ИВ-41AM system could influence the crew decision on engine cut-off. 
     The destruction of TsS-24 № Г872ВТ9 centrifugal breather was caused by the destruction of its spinner due to long-term exposure of air-oil emulsion with high temperature due to destruction of compressor rotor rear supprt structure bearing.
     Substantial secondary damage of the compressor rotor rear bearing section details didn't allow to determine the cause of the bearing destruction. Most probably the destruction was caused during its operation with higher races swash.
    Higher races swash could be caused by:
     - adverse combining of the compressor rotor rear bearing section beatings with bearing beating caused by incorrect installation during intermediate-level (according to technical condition) engine maintenance at "AARZ" JSC;
     - deviation from specifications of the compressor rotor rear bearing section geometry
    Contributing factors of the accident were:
     - PIC's psychological unreadiness to cut-off engine midair due to the lack of practice of actual flights with the engine out; 
     - late fire detection by the crew followed by untimely decision on fire extinguishing.
    Due to insufficient objective information it wasn't possible to determine the cause of late fire detection by the crew and evaluate operability of SSP-7 and SSP-2 all fire warning system components.
    The appropriate safety recommendations based on the investigation results were developed.