Event Details


Title:Uncontained engine failure, Fokker F27 Mk 500 Friendship, G-CEFX
Micro summary:This Fokker F27 Mk 500 experienced an uncontained engine failure on takeoff.
Event Time:2001-06-05 at 1049 UTC
File Name:2001-06-05-UK.pdf
Publishing Agency:Aircraft Accident Investigation Board (AAIB)
Publishing Country:United Kingdom
Report number:EW/C2001/6/5
Pages:55
Site of event:Takeoff, Jersey Airport, Channel Islands
Latitude/Longitude:04912.4'N 00212.6'W
Departure:Jersey Airport, Jersey, Channel Islands
Destination:Bournemouth International Airport, Bournemouth, England
Airplane Type(s):Fokker F-27 Mk 500 Friendship
Flight Phase:Takeoff
Registration(s):G-CEXF
Operator(s):Channel Express
Type of flight:Revenue
Occupants:3
Fatalities:0
Serious Injuries:0
Minor/Non-Injured:3
Other Injuries:0
Executive Summary:Shortly after takeoff from Runway 27 at Jersey Airport on an empty positioning flight to Bournemouth with three crew members on board, an uncontained failure occurred to the left engine at an altitude of approximately 670 feet. This resulted in a sudden and complete loss of power from the left engine and a major fire external to the nacelle, but this was extinguished during the Engine Fire Drill as the Low Pressure (LP) fuel cock was closed. The aircraft completed a left hand circuit and landed uneventfully back on Runway 27. The engine failure was caused by high cycle fatigue (HCF) cracking of the High Pressure Turbine (HPT) disc. Five similar Dart HPT failures had occurred over the previous 29 years, the most recent at London Stansted Airport on 30 March 1998 to an engine fitted in a HS 748 - Series 2 aircraft, G-OJEM. (AAIB Air Accident Report No: 3/2001.) Prior to that accident, the failures had been attributed to a combination of turbine entry flow distortion and turbine blade wear and the engine manufacturer and the CAA had concluded that the likely period before recurrence of failure was such that additional remedial action was unnecessary. While the engine failure in G-OJEM was initially attributed by the engine manufacturer to the same causes as the previous cases, major difficulty was experienced in confirming the likely causes. Following the necessarily protracted study, testing and analysis by the engine manufacturer, the evidence collected then indicated that a small gap, under running conditions, between the seal arm abutment faces of the HPT and Intermediate Pressure Turbine (IPT) discs could result in high cyclic stresses being present in the HPT seal arm radius at the disc diaphragm, and that these stresses could result in high cycle fatigue (HCF) cracking.

As a result of this, a manufacturer's Service Bulletin (SB), Modification No 1946, was issued in April 2001 and this was mandated by the CAA as an Airworthiness Directive. This modified the HPT to ensure that a positive interference or 'nip' would exist between the HPT and IPT disc seal arm abutment faces, as this was found to significantly reduce such damaging cyclic stresses. The compliance date of this SB was 'not later than 31 December 2005'. Following the HPT disc failure to G-CEXF, which had not yet been modified, the SB was changed to a cycles based requirement, essentially with the highest cycle discs being removed from service first, and with a compliance end date of 30 June 2004. Additional study has suggested a correlation may exist between the fit of the taper bolts, which clamp the three turbine discs together, and excessive seal arm wear found during routine overhauls, although insufficient evidence was available to determine the fit of the taper bolts on the HPT from G-CEXF. This has resulted in the manufacturer amending the relevant Overhaul Manual (OM) to take account of, amongst other process changes, the individual fit of these bolts to each turbine disc.
Learning Keywords:Operations - Maintenance
Systems - Engine - Uncontained Engine Failure
Other - Certification
Close match:In-flight loss of propeller blade, forced landing, and collision with terrain, Atlantic Southeast Airlines, Inc., Flight 529, Embraer EMB-120RT, N256AS, Carrollton, Georgia, August 21, 1995

 




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