Narrative:
The Boeing was operated on a military logistic flight from Tehran to McGuire AFB via Madrid. The flight took off from Tehran at 08:20 GMT and climbed to a cruising altitude of FL330. After establishing contact with Madrid control, clearance was received to CPL VOR via Castejon. At 14:25 the flight was cleared to FL100. At 14:30 the crew advised Madrid that they were diverting to the left because of thunderstorm activity, and at 14:32 Madrid cleared ULF48 to 5000 feet and directed him to contact Madrid approach control. At 14:33 the crew contacted approach control and advised them that there was too much weather activity ahead and requested to be vectored around it. Last radio contact was when ULF48 acknowledged the 260deg heading instructions and informed Madrid that they were descending to 5000 feet. The aircraft was later found to have crashed in farmland at 3000 feet msl following left wing separation.
It appeared that the aircraft had been struck by lightning, entering a forward part of the aircraft and exiting from a static discharger on the left wingtip. The lightning current's conductive path to the static discharger at the tip was through a bond strap along the trailing edge. Concentration of current at the riveted joint between this bond strap and a wing rib were sufficient conductive to cause the flash to reattach to this rivet and to leave the discharger. Fuel vapors in the no. 1 fuel tank then ignited. The explosion caused the upper wing skin panel to separate, causing a drastic altering of the aero elastic properties of the wing, and especially the outboard section of wing. The outer wing began to oscillate, developing loads which caused the high-frequency antenna and outer tip to separate. The whole wing failed a little later.
Fuel tank explosion
Wing failure
Loss of control
» ICAO Circular 146-AN/96 (116-140)
» NTSB-AAR-78-12
accident date: 09-05-1976
type: Boeing 747-131F
registration: N53111
| Status: | Accident investigation report completed and information captured |
| Date: | Sunday 9 May 1976 |
| Time: | 14:35 UTC |
| Type: |  Boeing 747-131F |
| Operator: | Imperial Iranian Air Force - IIAF |
| Registration: | 5-283 |
| MSN: | 19677/73 |
| First flight: | 1970-09-15 (5 years 8 months) |
| Engines: | 4 Pratt & Whitney JT9D-7A |
| Crew: | Fatalities: 10 / Occupants: 10 |
| Passengers: | Fatalities: 7 / Occupants: 7 |
| Total: | Fatalities: 17 / Occupants: 17 |
| Aircraft damage: | Destroyed |
| Aircraft fate: | Written off (damaged beyond repair) |
| Location: | near Madrid ( Spain)
|
| Phase: | En route (ENR) |
| Nature: | Cargo |
| Departure airport: | Tehran-Mehrabad Airport (THR/OIII), Iran |
| Madrid-Torrejón AFB (TOJ/LETO), Spain | |
| Flightnumber: | ULF48 |
The Boeing was operated on a military logistic flight from Tehran to McGuire AFB via Madrid. The flight took off from Tehran at 08:20 GMT and climbed to a cruising altitude of FL330. After establishing contact with Madrid control, clearance was received to CPL VOR via Castejon. At 14:25 the flight was cleared to FL100. At 14:30 the crew advised Madrid that they were diverting to the left because of thunderstorm activity, and at 14:32 Madrid cleared ULF48 to 5000 feet and directed him to contact Madrid approach control. At 14:33 the crew contacted approach control and advised them that there was too much weather activity ahead and requested to be vectored around it. Last radio contact was when ULF48 acknowledged the 260deg heading instructions and informed Madrid that they were descending to 5000 feet. The aircraft was later found to have crashed in farmland at 3000 feet msl following left wing separation.
It appeared that the aircraft had been struck by lightning, entering a forward part of the aircraft and exiting from a static discharger on the left wingtip. The lightning current's conductive path to the static discharger at the tip was through a bond strap along the trailing edge. Concentration of current at the riveted joint between this bond strap and a wing rib were sufficient conductive to cause the flash to reattach to this rivet and to leave the discharger. Fuel vapors in the no. 1 fuel tank then ignited. The explosion caused the upper wing skin panel to separate, causing a drastic altering of the aero elastic properties of the wing, and especially the outboard section of wing. The outer wing began to oscillate, developing loads which caused the high-frequency antenna and outer tip to separate. The whole wing failed a little later.
Accident investigation:
 |
|
Classification:
LightningstrikeFuel tank explosion
Wing failure
Loss of control
Sources:
» Flight International 15 May 1976 (1283)» ICAO Circular 146-AN/96 (116-140)
» NTSB-AAR-78-12
Photos
accident date: 09-05-1976
type: Boeing 747-131F
registration: N53111
Map
This map shows the airport of departure and the intended destination of the flight. The line between the airports does not display the exact flight path.
Distance from Tehran-Mehrabad Airport to Madrid-Torrejón AFB as the crow flies is 4713 km (2946 miles).
Accident location: Global; accuracy within tens or hundreds of kilometers.
Distance from Tehran-Mehrabad Airport to Madrid-Torrejón AFB as the crow flies is 4713 km (2946 miles).
Accident location: Global; accuracy within tens or hundreds of kilometers.
This information is not presented as the Flight Safety Foundation or the Aviation Safety Network’s opinion as to the cause of the accident. It is preliminary and is based on the facts as they are known at this time.
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Boeing 747
- 1551+ built
- 5th loss
- 2nd fatal accident
- 2nd worst accident (at the time)
- 18th worst accident (currently)
Spain- 18th worst accident (at the time)
- 28th worst accident (currently)
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