Accident description
Last updated: 29 July 2014
Status:Final
Date:Sunday 9 May 1976
Time:14:35 UTC
Type:Boeing 747-131F
Operator:Imperial Iranian Air Force - IIAF
Registration: 5-8104
C/n / 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
Airplane damage: Damaged beyond repair
Location:near Madrid (   Spain) show on map
Phase: En route (ENR)
Nature:Cargo
Departure airport:Tehran-Mehrabad Airport (THR/OIII), Iran
Destination airport:Madrid-Torrejón AFB (TOJ/LETO), Spain
Flightnumber: 48
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.


Classification:
Lightningstrike

Wing failure
Loss of control

Sources:
» Flight International 15.5.76(1283)
» ICAO Circular 146-AN/96 (116-140)
» NTSB-AAR-78-12

Official accident investigation report
investigating agency: National Transport Safety Bureau (NTSB) - USA
report status: Final
report number: NTSB/AAR-78-12
report released:06-OCT-1978
duration of investigation:880 days (2 years 5 months)
download report: Special Investigative Report: Wing Failure of Boeing 747-131, near Madrid, Spain, May 9, 1976. (NTSB/AAR-78-12)
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Photos

photo of Boeing 747-131F N53111
N53111 was sold to the Iranian Air Force in November 1975.
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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).

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