On 19 October 2009, a Boeing 737-300 being operated by British Midland subsidiary bmibaby on a scheduled passenger flight from Knock (also more recently known as ‘Ireland West’) to Manchester encountered a large flock of medium-sized birds during rotation for take off in normal day visibility and engine malfunction followed. Increasing engine vibration during the climb led to the decision to divert to Shannon, which was completed without further event. There were no injuries to the 133 occupants or anyone on the ground.
An Investigation was carried out by the Irish AAIU. Flight Data Recorder (FDR) data was available to assist the Investigation. Damage to No 1 engine was found to have been significant but damage to No2 engine only minor. Some engine debris was found near the site of the encounter.
The Investigation established that although birds had passed down both sides of the aircraft, increases in engine vibration had been mainly in respect of engine No 1. Initially these indications, whilst abnormal, had remained well within the band that requires no crew action and although they had increased as the aircraft climbed from FL70 to FL100, they remained below 4 on the five point scale, which is the level where Quick Reference Handbook (QRH) drills become applicable and normal use of engine thrust had therefore been maintained throughout the flight. It was apparent that most of the debris from No 1 engine had bypassed the engine core after passing through the fan blades.
The birds were identified as Lapwings and eight carcasses were recovered from the runway. Estimates of the size of` the complete flock were in the range 30 to 40 birds. The Aerodrome Manual was noted to contains the remark that “flocks of lapwing…. frequent the airport from November to March” and that “from a distance the presence of these flocks is apparent only when they are in flight”.
Bird patrols at the airport prior to the event were reviewed and it was found that after four patrols in the two hour period 1000 – 1200, none of which reported any bird activity, there has been no more before the departure of the incident aircraft at 1420, which had itself followed the departure of an Airbus A320 from the same runway six minutes earlier.
It was noted that under ‘Wildlife Hazard Management’, the Aerodrome Manual allocated the responsibility for day-to-day monitoring of bird activity on the airfield, and for reporting the presence of birds to the RFFS to elicit a response, to ATC. However, it also required that “routine day patrols as well as any patrols requested by ATC shall be carried out to ensure that bird hazard is controlled”. The aerodrome Manual of Air Traffic Services was noted to state that “Where possible, ATC should request bird patrols prior to the arrival or departure of scheduled or jet traffic (and any) observed bird activity on or near the aerodrome shall be brought to the attention of the Fire Service Duty Officer.”
The Investigation concluded that as “there is a relatively low level of commercial and jet aircraft activity at (this airport)…the requirement to carry out mobile patrols prior to aircraft movements is more appropriate there than it would be at airports with more intense traffic levels, where birds are likely to be disturbed by arriving and departing aircraft and thus be more visible to ATC and other airport personnel”. It also concluded in respect of the existing Aerodrome Manual advice that “when viewed from a distance the presence of flocks of lapwings is only apparent when they are in flight…..the requirement for patrols into areas where such flocks may become a hazard is more appropriate than observation from a distance, such as from a Control Tower”.
The Investigation concluded that the Probable Cause of the event was:
- Damage to both engines as a result of multiple bird strikes.
And that Contributory Causes were:
- The absence of a bird patrol immediately before the take-off of the aircraft.
- The discretion in requesting bird patrols afforded to ATC personnel by the Manual of Air Traffic Services.
It was noted that whilst the Investigation was in progress, the Airport Authority had
- Amended the Aerodrome Manual of Air Traffic Services to state that “In order to minimise the impact of bird activity on aircraft operations, the Duty ATCO shall initiate a bird patrol prior to the arrival or departure of scheduled or jet traffic”.
- By means of a Safety Bulletin reminder all staff of their responsibilities in respect of bird strike risk management.
The first action above was specifically endorsed by the Investigation and “accordingly, the Investigation considers that there is no requirement for a further Safety Recommendation in this respect”.
The Final Report: AAIU Report No: 2011-002 of the Investigation was published on 24 January 2011.