On 6 December 1997, a British Airways Boeing 747-100, departing from London Heathrow airport, had an engine bird strike just after take off, causing substantial damage and falling debris.
The following are extracts from the official AAIB report, which sustained five Safety Recommendations concerning bird strike risk assessment and aircraft powerplant certification.
"The aircraft was cleared to take off at 1446 hrs and the initial part of the take off run was normal. At a speed between V1 and Vr the commander saw a large bird ahead of the aircraft flying from right to left. He called "Rotate" at the correct speed, at which point the bird was on the left side of the aircraft but it then appeared to veer back and upwards towards the aircraft. All three crew members felt a pronounced 'thump' at about 100 feet agl, at which time the speed was estimated to be 165 KIAS. Almost immediately the Exhaust Gas Temperature for the No 2 engine rose rapidly, exceeding the maximum limit, and the crew noted that the other engine parameters for the No 2 engine also indicated damage to that engine. None of the other engines showed any unusual indications and the FO encountered no significant handling problems in controlling the aircraft. The crew of another aircraft which had been cleared for take off…saw debris fall from the inboard left engine of the incident aircraft…
The gear was selected up and the aircraft was climbed straight ahead as the crew confirmed the engine failure. Once above 400 feet agl the drill for 'Engine fire, severe damage or separation' was initiated for the No 2 engine and the FO transmitted a Pan call…informing ATC of the engine failure; this call was acknowledged by the controller. The FO engaged the autopilot, the commander took control of the radio and upon reaching 4,000 feet they were given radar vectors towards the south coast. They were offered a discrete frequency, but declined because the frequency they were then operating was very quiet. The flight engineer confirmed that the Checklist items for an 'Engine fire, severe failure or separation' had been completed and then carried out the associated drills followed by the after take off checks. …The cabin services director had already reported to the flight deck that the cabin crew had witnessed significant damage to the No 2 engine.
The aircraft was levelled at FL120 over the sea to the south of the Seaford VOR and 50,000 kg of fuel was jettisoned to reduce the aircraft weight to the maximum for landing. When the jettison drill had been completed the flight engineer went back into the passenger cabin to conduct a visual inspection of the No 2 engine and noted that the intake nose cowl and the fan cowls were missing; he did not observe any related damage to the airframe. Although there were no apparent hydraulic or flap/slat problems, the crew decided that they would reduce the speed early at every stage of the subsequent approach in order to detect any handling problems as soon as possible. Whilst in the holding pattern, which was flown at 260 KIAS in the clean configuration, there was noticeable airframe vibration. The vibration level increased as speed was reduced and flap progressively extended and was most marked at 205 KIAS with flaps 5. However, the level of vibration did not affect the operation of the aircraft and the crew did not experience any difficulty in reading the flight deck instruments. The commander positioned the aircraft for an ILS approach to Runway 27L with flap 25 selected; the approach and landing were normal with full reverse selected on the outboard engines after touchdown…
…Initial examination…showed that the left inner (No 2) engine had suffered severe damage to the fan; two adjacent fan blades had lost substantial portions of their outer length and all the blades had some hard object damage. It was also observed that the complete intake assembly, fan cowls, jet pipe and exhaust cone had separated from the powerplant assembly; these components, together with fragments of fan blade and some feathered bird remains were retrieved from the western end of Runway 27R…The feathers…were identified as having come from a Grey Heron.
…The overall damage to the engine was sufficient to render it beyond economic repair.
…Typical Grey Herons fall into the weight range of 1.3 to 1.6 kg. and as such are regarded as large birds. The Pratt and Whitney JT9D engine was granted Type Approval by the FAA to earlier requirements in which the criteria for tolerance to the ingestion of large birds was specified in Advisory Circular 33-1A and was certificated by a test using two, 2 lbs birds. However, its performance in this incident indicated that the basic engine would probably have met current requirements for this category of engine."
"Whilst the primary cause of this incident was the ingestion by the right engine of a single 'large' bird which had approached the western area of Runway 27R undetected, it is apparent that there is a growing population of large birds adjacent to Heathrow Airport which poses an increasing hazard to aircraft. It is evident that the scale of this hazard needs to be quantified and improved measures devised to control the bird population in the short term and to further protect public transport aircraft using the Airport. An effective automated Airport system to detect large birds about to transit across the Airport could enable the pilots of departing or arriving aircraft to be alerted to potential multiple birdstrike conflicts. Such a future development could reduce the risk of a related large scale accident in the congested vicinity of the airport as a result of associated multiple engine damage, and also reduce the commercial costs of damage arising from lesser birdstrike incidents."
As a result of such concerns and considerations, the following Safety Recommendations are made:
- Recommendation 98-58 In view of the apparent increased incidence of large bird formation (e.g. Canada Geese) transit flying over London Heathrow Airport, with the attendant increasing risk of multiple birdstrike occurrence involving departing or arriving public transport aircraft, it is recommended that Heathrow Airport Limited and the CAA should set up a working group, in conjunction with Airport Operators, to review available technology to determine if a radar based large bird flock detection system, or an alternative automated system, could more effectively alert pilots and ATC to potential multiple birdstrike encounters.
- Recommendation 98-59 In order to reduce the risk of multiple large birdstrike encounters, involving bird formations overflying London Heathrow Airport conflicting with departing or arriving public transport aircraft, Heathrow Airport Limited should seek maximum cooperation with the relevant local authority bodies and associated land owners to expedite effective management of the associated large bird habitat and population around Heathrow Airport. Similar co-operative initiatives should be actively promoted by the CAA around other affected major airports in the UK.
- Recommendation 99-18 The CAA should expand the remit of its sponsored current study by the Central Science Laboratory Birdstrike Avoidance Team of the habitat, population and transit flight behaviour of flocking large bird species around Heathrow Airport to include the formulation of recommendations on the best means of managing and reducing the associated hazard of multiple birdstrike encounters involving departing or arriving public transport aircraft.
In addition, since the detachment of large heavy engine nacelle parts from aircraft in flight poses a serious hazard to populated areas being overflown, the following Safety Recommendations are made:
- Recommendation 98-60 In order to reduce the likelihood of large intake assemblies suffering in-flight detachment from Pratt and Whitney JT9 powerplants on Boeing 747 aircraft as a result of bird ingestion damage induced vibration effects, the aircraft manufacturer should be review the reduction in the number of associated intake attachment bolts (from 74 to 37) which was introduced by Service Bulletin 747-71-2065 to ease intake interchange.
- Recommendation 98-61 The current engine certification requirements, FAR 33.77 and JAR-E 800, should be amended to require that large nacelle components remain attached to the engine up to the limit of forces on the engine and nacelle which result in the detachment of the entire nacelle from its pylon or wing attachments.