A Boeing 757-236 was being operated on a scheduled passenger flight from Glasgow (Scotland) to London (England), on this day in 1993. After all the preparations were completed the aircraft taxied to the runway and after receiving the take-off clearance an uneventful take-off run and lift off followed.
The missing panels on the right-hand wing-to-body fairing (source & © AAIB)
During the climb out, for a short period of time, a vibration was felt by the crew. By the time the aircraft reached an altitude of 7000 feet (2100 meters) `the vibrations ceased. During the time of the vibrations, and afterwards, there were no abnormal system indications, cautions or warnings presented to the crew. Based on the lack of alerts and the absence of the vibrations the crew decided to continue to London Heathrow. The flight was uneventful until the aircraft was on the approach to London Heathrow when the crew observed higher than normal vibrations in the airframe.
Apart from the vibrations the remainder of the approach and the landing were uneventful, and after landing the aircraft taxied to its parking position. During an external inspection of the aircraft, it was found that a part of the right-hand wing to body fairing had separated from the aircraft.
The GRP/Hineycomp (Glassfibre Reinforced Plastic) panel that initially separated from the aircraft, measured 3 feet x 4,5 feet (91 cm x 137 cm). This led to the loss of a second panel, L-shaped measuring approximately 5 feet x 5 feet (152 cm x 152 cm). The remnant of the panels fell down into the playground of a primary school, luckily nobody in the playground sustained physical injuries. The panels were transported to London Heathrow and were inspected in conjunction with the damage to the aircraft. The panel was normally secured to the aircraft along with three out of four sides with a row of countersunk fasteners, with the top edge free to move along the fuselage.
Close up of the missing panels (Source & © AAIB)
It was determined that a considerable amount of fasteners had not been installed on the panels, mainly on the leading edge of the panel. This was based on the lack of damage to the fastener holes on the panels A subsequent test of the friction locking properties of the anchor nuts on the aircraft to determine the ability to retain the fasteners s was carried out. This test revealed that all the nuts associated with fasteners that were missing on the aircraft had lost their locking properties.
The fasteners could be screwed in and out without any effort using finger strength.
As a result of this finding, the operator carried out a fleetwide check, which revealed that on 75% of the fleet the particular panels had loose or missing fasteners. These and other findings resulted in an amended maintenance program for the operator's Boeing 757 fleet. More details on this incident are available in the report on the incident which was published by the British Air Accident Investigation Branch. Click here for access to the report.