Date:	Sunday 9 May 1976
Time:	14:35
Type:	Boeing 747-131F
Owner/operator:	Imperial Iranian Air Force - IIAF
Registration:	5-283
MSN:	19677/73
Year of manufacture:	1970
Engine model:	Pratt & Whitney JT9D-7A
Fatalities:	Fatalities: 17 / Occupants: 17
Aircraft damage:	Destroyed, written off
Category:	Accident
Location:	near Madrid -   Spain
Phase:	En route
Nature:	Cargo
Departure airport:	Tehran-Mehrabad Airport (THR/OIII)
Destination airport:	Madrid-Torrejón AFB (TOJ/LETO)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

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.

Flight International 15 May 1976 (1283)
ICAO Circular 146-AN/96 (116-140)
NTSB-AAR-78-12

photo (c) via Werner Fischdick; Frankfurt International Airport (FRA); December 1974

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