A Sikorsky S-61N-II helicopter was on standby in a Coastguard role out of the Royal Marine Barracks Poole, in Dorset (United Kingdom) on this day in 2002. After completing the necessary preflight checks from 08.00 lt (local time) the crew (two pilots a winch operator and a winchman) was on standby.
The aircraft wreckage after the fire was extinguished (Source AAIB © Unknown)
At 14.25 lt the crew was scrambled for a person in the water in Poole Harbour, 5 minutes later the aircraft was airborne and heading for Poole Harbour. Once on site, a search pattern was established over the harbour at ~200 feet at a speed varying from 20 to 80 knots. 40 minutes after arriving over Pool Harbour the crew was directed to a ship emitting a lot of smoke, north of Pool Harbour. Shortly afterwards an unusual sound (hissing) was noticed by the crew in the cabin, their call to the pilots about their observation was followed immediately with ‘NO 2 ENG FIRE WARN’ and ‘No 2 T HANDLE’ lights. After confirming the right Speed Select lever was held by the co-pilot the #2 SPEED SELECT lever was moved to the idle and then the Cut-off position. Subsequently, the fire extinguisher for the #2 engine was discharged. ATC and the Coastguard were informed of their situation while the commander turned the aircraft towards Bournemouth Airport. While heading for Bournemouth the co-pilot informed the commander the ‘NO 2 ENG FIRE WARN’ was still on and a possible landing sight was on their left.
The main gearbox and No 1 engine (source AAIB © unknown)
This was followed by a ‘TRANS OIL PRESS’ light and not long after by a ‘PRI SERVO PRESS’ light illuminated followed by the illumination of the ‘AUX SERVO PRESS’ light. As the commander noticed an uncommanded movement of the cyclic control he called for an immediate landing on a sports field. On the final approach, the co-pilot extended the landing gear when the commander called "Fire in No 1". The aircraft touched down at speed of 10 knots coming to a stop after a ground roll of 30 meters although the brakes had failed~. The No 1 engine was shut down and the rotor-brake was applied. The shutdown was completed and all crew evacuated the aircraft. When the fire brigade arrived all they could do was extinguish the flames. The aircraft was lost to the flames. The time between the onset of the original fire warning and touchdown was 82 seconds.
The accident was investigated by the AAIB (Air Accident Investigation Branch), in their report, published in March 2004, they 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. The AAIB report is available by clicking here.
The aircraft in better days (Source airliners.net © Alan McKnight)
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