28th of July 1994

With 267 passengers and 18 crew, a Boeing 747-238 was scheduled to operate a flight from San Francisco (California, USA) to London Heathrow Airport (United Kingdom). After an uneventful flight across the Atlantic Ocean, ATC instructed the flight to enter a holding pattern over the Bovingdon Airfield (North-west of London).

The damaged tip, as seen from the ground (© AAIB, amended by V2 Aviation - Training & Maintenance)

Upon entering the holding the captain as pilot flying (PF) noted there was some rain and turbulence over the beacon. The seatbelt sign was switched and the aircraft entered the holding pattern. While in the holding pattern at FL100 a load "BOOM" was heard through the aircraft while the whole aircraft shuddered. (Flight Level 100 = 10.000 feet above mean sea level when the pressure at sea level is 1013.2 mb)

By experience, the crew realised the aircraft had been hit by lightning. Al aircraft systems appeared to be operating as normal, and handling of the aircraft was normal. The captain, therefore, instructed the flight engineer to inform the passengers that there had been a lightning strike but everything was operating normally and there was no reason for anxiety. The crew did not inform ATC as there was no apparent issue with the aircraft systems. After a short time in the holding pattern, ATC vectored the aircraft for an ILS approach to one of Heathrow's runways. On final approach, it became apparent that both the ILS Glideslope indications were working normally, but neither of the ILS Localiser indications was available, they appeared not to receive a signal.

As the crew was in visual contact with the runway they requested a visual approach and landing, which was approved by ATC. An uneventful landing was completed. When the crew disembarked the aircraft the captain noticed that the top of the vertical stabiliser was missing.

Close-up of the damaged tip of the vertical fin (© AAIB) A subsequent investigation by maintenance staff revealed that the GRP fin cap (GRP = Glass-Fibre Reinforced Plastic) was indeed missing and that the VOR/Localiser antenna, located in the fin cap) had totally been destroyed. Furter structural damage was found to the area of the fin, above the rudder. The VOR/Localiser receivers were replaced before the flight, although a self-test of the receivers was carried out without fault. All other damage was repaired before the aircraft was returned to service. A field investigation into the lightning strike was completed by the Air Accident Investigation Branch, their report is available for your information by clicking here.

The severely damaged antenna assembly (© AAIB)

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