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AIR ACCIDENTS INVESTIGATION INSTITUTE

Covering form of preliminary or final report


Date of event : 2015-04-08
Incident number :
Report : Final report
Place of event : 15 NM SW from LKKT
Registration mark : Serious incident
Weight category MTOM: : 2250 – 5700 kg
Type of operation : other
Plane / SFM : Airplanes
Type of plane / SFM : SHORTS SC7 SKYVAN
Health effects of event : Without injury
PDF document : pdf

Description:

On 8 April 2015, while the foreign operator’s Skyvan was flying from the Landsberg aerodrome to the Klatovy aerodrome, approximately when crossing the national border of the Czech Republic, the crew overheard a bang coming from the right side of the aircraft. It was accompanied with RPM, torque and oil pressure drop in the right engine. Simultaneously, smoke was blowing from the rear part of the right engine. Shortly afterwards, the cockpit smelt of fuel and continuous depletion of the amount of fuel in the right tank was observed. Upon emergence of the critical event, the instructor took over control, applied single-engine flight procedures and completed the flight at LKKT. Landing was successful. While the aircraft was taxiing to the stand, ground became contaminated with leaking fuel.

The cause of the serious incident was the total loss of power of the right engine due to an infringement of the integrity of the 2nd and 3rd stage of the turbine, which led to a penetration of the combustor plenum, damage to the fuel tanks of the aircraft and engine shutdown. The turbine wheel fracture mechanism could not be determined due to lack of evidence. On 3rd stage of the turbine, there was a crack due to the fatigue fracture that emanated from the corner of the rivet.

Factors that may have affected the failure:

  • the absence of the airplane operations data led to the fact that during the rebuilding of the engine in 2004 there was no correction of the baseline for the calculation of the equivalent cycles worked around the 3rd stage of the turbine and consequently the exceeding of the lifetime of the third stage turbine set by the manufacturer.
  • during inspections by FPI the rivets in the 3rd stage turbine wheel holes have not been removed, which was not in accordance with the maintenance manual, and this could reduce the appearance of cracks.