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S61, vicinity Bournemouth UK, 2002

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Summary
On 15 July 2002, a Sikorsky S-61 helicopter operated by Bristow suffered a catastrophic engine failure and fire. After an emergency landing and evacuation, the aircraft was destroyed by an intense fire.
Event Details
When July 2002
Actual or Potential
Event Type
Airworthiness, Fire Smoke and Fumes
Day/Night Day
Flight Conditions VMC
Flight Details
Aircraft SIKORSKY S-61
Operator Bristow Helicopters
Domicile United Kingdom
Type of Flight Aerial Work
Origin RNAS Portland Heliport
Intended Destination RNAS Portland Heliport
Take off Commenced Yes
Flight Airborne Yes
Flight Completed No
Flight Phase Cruise
ENR
Location - Airport
Airport vicinity Bournemouth Airport
FIRE
Tag(s) Fire-Power Plant origin
AW
System(s) Engine - General
Contributor(s) Component Fault in service
Outcome
Damage or injury Yes
Aircraft damage Hull loss
Non-aircraft damage Yes
Injuries None"None" is not in the list (Few occupants, Many occupants, Most or all occupants) of allowed values for the "Injuries" property.
Fatalities None"None" is not in the list (Few occupants, Many occupants, Most or all occupants) of allowed values for the "Fatalities" property. ()
Off Airport Landing Yes
Causal Factor Group(s)
Group(s) Aircraft Technical
Safety Recommendation(s)
Group(s) Aircraft Airworthiness
Investigation Type
Type Independent

Description

On 15 July 2002, a Sikorsky S-61 helicopter operated by Bristow suffered a catastrophic engine failure and fire. After an emergency landing and evacuation, the aircraft was destroyed by an intense fire.

Synopsis

The following is an extract from the synopsis is taken from the official Aircraft Accident Investigation Branch (UK) (AAIB) accident report:

"G-BBHM, which was based at Portland, was being operated in the Search and Rescue role. Following the first alert of the day, G-BBHM had been airborne for about 40 minutes over Poole Harbour when the two rear crew members became aware of an unusual noise. Almost immediately, the pilots saw the ‘NO 2 ENG FIRE WARN’ light illuminate accompanied by the audio alert. The pilots commenced their emergency procedures, including shutting down the No 2 engine and activating the fire extinguisher, and initially set heading for Bournemouth Airport. However, with the ‘FIRE’ light still illuminated and indications of hydraulic failures from both tactile and warning systems, the co-pilot alerted the commander to a suitable nearby landing area. The commander called for an immediate landing and made a successful approach and touchdown; during the approach, the pilots became aware that ‘NO 1 ENG FIRE WARN’ was also illuminated. After touchdown, the pilots shut down the No 1 engine and the crew quickly vacated the helicopter. G-BBHM was destroyed by fire shortly after they were clear. The time between the onset of the original fire warning and touchdown was 82 seconds."

The investigation identified the following causal factors:

  • "The No 2 engine had suffered rapid deterioration of the No 5 (location) bearing of the free turbine, causing failure of the adjacent carbon oil seal and mechanical interference between the Main Drive Shaft Thomas coupling and the Engine Mounting Rear Support Assembly tube, which completely severed the support tube.
  • A severe fire, outside of the engine fire zone, was caused because the released engine oil was ignited either by this mechanical interference, or by contact with the hot engine exhaust duct.
  • The No 2 engine’s No 5 bearing failed because of unusual and excessive cyclic loading conditions arising from shaft vibration. The bearing deterioration was exacerbated by a reduction in its oil supply during the same period, when the live oil jet fractured as a consequence of the vibration.
  • It is probable that the Main Drive Shaft vibration was caused by damage or distortion sustained during one or more previous No 2 engine starts involving a high torque rotor engagement.
  • There was no specific torque limitation published in the manufacturer’s Flight Manual, used by Bristow Helicopters Limited, during rotor engagement after engine start."

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