History of the Flight
The flight from Cork to London Heathrow proceeded without incident until approaching the Ockham VOR, when the Hydraulic and Master Caution lights flickered and then extinguished. The first officer noted that the System B quantity indicated 39%. The crew requested ATC permission to hold while assessing the situation. During the hold, the crew informed ATC that the problem involved one hydraulic system and completed the appropriate checklist. Flap 5 was selected and speed reduced to 180 kt. The crew classified the situation as abnormal, not an emergency, and did not declare a 'Pan' or 'Mayday'. The Senior Cabin Crew Member (SCCM) was briefed that the landing would be normal but at a slightly higher speed, with emergency services in attendance.
The commander made a PA announcement to passengers about the hydraulic failure and the need for a faster landing with emergency vehicles present. ATC was informed of readiness for approach, and the crew requested to join the final approach at 10 miles. Two aircraft were vectored ahead of the flight on Runway 27L, with none behind, in case the runway became blocked. A discrete frequency (121.6 MHz) was provided for communication with Rescue and Fire Fighting Services (RFSS).
Landing and Evacuation
An auto-coupled approach led to an uneventful landing. Reverse thrust (80% N1) and manual braking were used, stopping the aircraft slightly beyond the normal turn-off point. The commander made a PA for passengers to remain seated, indicating no evacuation was necessary. The first officer requested a thorough inspection of the landing gear and aircraft by RFSS. The commander shut down both engines and secured the aircraft as fire personnel approached. RFSS reported smoke from the left side; the commander then requested confirmation and the Fire Chief noted smoke from the right side as well. Based on this, the commander decided to evacuate and informed the first officer. The SCCM, hearing the word 'evacuate', asked for confirmation and then made a PA: 'cabin crew evacuate the aircraft'. The commander did not activate the 'Evac Alert' system as the evacuation was already underway.
All doors were used except door 1 Right, where the slide inflated fully but tilted forward and was not usable. Overwing exits were initially used, but passengers faced a significant drop because flaps were at Flap 15 (as per the Quick Reference Handbook for a B system hydraulic failure). RFSS, assessing no immediate danger, redirected passengers back into the aircraft to use slide exits. Cabin and flight deck crew checked the entire cabin and toilets before evacuating via slides.
One infant, carried by a passenger, stopped breathing at the slide’s end but was revived by mouth and nose resuscitation from a fire officer. Another passenger sustained slight back injuries from exiting the slide. Both were taken to hospital but not detained. Passengers were assembled in groups, with minors kept together, and buses transported them to the terminal.
Technical Findings
Examination revealed the hydraulic 'B' system pump (P/N 5718F03) had failed due to damage to a plug and bleeder 'O' ring seal (P/N NAS1612-4). The damaged 'O' ring exhibited flattening on the side facing the belleville washer. Another pump with an 'O' ring from the same batch showed similar flattening but recovered shape overnight. Six 'O' rings were sent for testing, including the failed ring, one from the same batch removed from a serviceable pump, a ring from the 'bad batch', and three from batch 1034521 for comparison. The defective ring failed due to mould misforming. The ring from the same batch had been heavily buffed to remove excess flash, and another from batch 1034562 also showed buffing. The three rings from batch 1034521 had no defects. The exact cause was either a pinched seal on assembly or a manufacturing fault from buffing. The entire batch of 'O' rings was withdrawn from service.
Slide Malfunction
The failure of door 1 Right slide to deploy correctly was investigated. The slide was repacked by the same individual who had previously packed it and refitted. A cabin crew member opened the door and the slide deployed flawlessly. It was considered that requiring the manual inflation handle to be pulled regardless of automatic inflation could hazard cabin crew due to common system parts.
Safety Actions
The operator took several follow-up actions, including:
- Purging all stock and aircraft-fitted 'O' rings of batch number 1034562.
- Issuing instructions to personnel emphasizing avoidance of pinching the seal on assembly.
- Stressing the need for a single movement when opening doors to ensure correct slide operation.
- Re-examining the procedure for cabin crew to immediately pull the manual inflation handle of escape slides regardless of automatic inflation.