Incident
On 3 December 1999, at approximately 1605 UTC, a large metal object fell on a house in Mansfield, Nottingham, damaging the back door. The object, measuring about 1.5 metres by 0.5 metres and weighing roughly 25 lb, was later identified as a strut-to-aft fairing seal assembly from a Boeing 757-236, registration G-BIKJ. The aircraft was operating a public transport flight from London Heathrow Airport to Glasgow. The flight crew was unaware of the detachment.
Examination
Two days after the incident, during a ramp inspection at London Heathrow, an engineer noticed the missing seal assembly on the aircraft's engine pylon. The operator's maintenance personnel examined the assembly and found no evidence that the retaining bolt had been engaged; the bolt was not recovered. The associated engine on G-BIKJ had been changed on 16 November 1999, which was the last time the seal would have been disturbed.
Previous Occurrences
Similar detachments of the strut-to-aft fairing seal assembly had occurred on other aircraft of the same type due to apparent non-fitment of the retaining bolt. One such incident was reported in AAIB Bulletin 2/97 involving aircraft G-BIKF.
Modifications
In response to this incident, the operator introduced a modification to prevent recurrence. The modification adds a hole in the existing bolt head to allow wirelocking, or alternatively permits the use of a different bolt with a pre-existing hole for the same purpose. The operator intended to modify its entire fleet within two weeks of this incident. Additionally, consideration was being given to another modification introducing a modified seal catch retainer.