'Clipper One' Pan American's scheduled service from London Heathrow Airport to New York J.F. Kennedy Airport ran into a minor delay due to a last-minute fuel uplift do on this Day in Aviation History. With 392 passengers and 15 crew onboard the engines of the Boeing 747-100, N656PA, were started at 13.52lt.
After an uneventful start of the engines the aircraft taxies to Runway 28R and receives its take-off clearance at 14.09lt. The captain, who was pilot flying) set the throttles to achieve 1.1 EPR, and confirmed all engines spooled up. He then set the throttle to the take-off setting for the calculated take-off thrust 1.44 EPR.
After brake release, as per procedure, when transferring throttle control to the flight engineer, a loud bang was heard from the right-hand side of the aircraft. The Captain closed the throttles and aborted the take-off, at low speed. No reverse thrust of heavy braking was used to slow the aircraft down. Without any further warning on a failure, cockpit indications made it clear to the crew engine number #3 (right-hand inboard) was the cause of the loud noise, and the engine was shut down before the aircraft taxied to the terminal where the passengers were disembarked.
The cracked combuster casing (source www.aaib.go.uk)
A detailed inspection of the aircraft revealed major damage to the aircraft;
#3 engine inner cowling doors blown off
#3 engine casing ruptured
#3 engine starter, oil tank and pneumatic ducting torn off the engine
Slat inboard of engine #3 damaged
#3 engine pylon punctured
#4 engine 1 fan blade damaged
1 cut tire
As the CVR was not isolated until 45 minutes after the incident the voice data was overwritten. The Digital Flight Data Recorder had recorded the EPR values for the engines, with the exception for engine #3 the other engines had been achieved 1.44 EPR, the #3 engine EPR was recorded to be 13% higher. It achieved an EPR of 1,57. The engine was replaced, the other damages were repaired and after the necessary tests, the aircraft was returned to revenue service.
A P&W JT9D cutaway, indicating the area of failure between flange K and M. (Source www.aaib.gov.uk)
The failed engine was sent to the PanAm engines shop for a stripdown. The primary failure of the engine was the failure of the engine (diffuser) casing between engine flange K and flange M, through flange L. This primary failure had a length of 33 inches (83 cm), with a separation up to 15 inches (38cm wide) at the widest point of the failure. The diffuser case was not a Life Limited Part and was only changed on condition. Investigators suspect a fatigue crack existed already in the casing, and when the engine reached 1,57 EPR (The reason for this high EPR is not explained in the investigation report which is available by clicking here).
A revised engine inspection, using a flexible horoscope, was introduced after the incident and an SB was issued by the engine manufacturer.