Imperial Iranian Air Force Flight 48

1976 military aviation accident

Imperial Iranian Air Force Flight 48
Accident
An Iranian Air Force 747 similar to the one involved in the accident showing the aircraft livery in use at the time
Date	May 9, 1976 (1976-05-09)
Summary	Fuel tank explosion caused by lightning strike; leading to separation of the left wing
Site	Near Adolfo Suárez Madrid–Barajas Airport, Madrid, Spain
Aircraft
Aircraft type	Boeing 747-131(SF)
Operator	Imperial Iranian Air Force operated by TWA
Registration	5-283
Flight origin	Tehran-Mehrabad Airport, Tehran, Iran
Stopover	Madrid–Barajas Airport, Madrid, Spain
Destination	McGuire Air Force Base, New Jersey, United States
Occupants	17
Passengers	7
Crew	10
Fatalities	17
Survivors	0

Imperial Iranian Air Force Flight 48 was a military cargo flight from Tehran, Iran, to McGuire Air Force Base in the United States with a stopover in Madrid, Spain. On May 9, 1976, the Boeing 747-131 freighter operating the flight crashed during its approach to Madrid, killing all 17 people on board.

Aircraft

The aircraft involved was a five year old Boeing 747-131 (serial number 19677 and line number 73) which made its first flight on September 15, 1970. On September 26, the aircraft was delivered to Trans World Airlines (TWA) with registration N53111.

On October 15, 1975, the aircraft was returned to the Boeing factory in Wichita, Kansas. It was converted into a freighter cargo model (747-131F), during which time a large cargo door was added on the left side.

In October 1975, the aircraft was sold to the Imperial Iranian Air Force with serial number 5-283. The IIAF received the aircraft on November 1. The aircraft was powered by four Pratt & Whitney JT9D-3B turbofan engines.

The aircraft's last maintenance check was performed by the Imperial Iranian Air Force on May 4, 1976, after which it flew for 16 hours. During the subsequent investigation, it would be determined that American specialists were unaware of the check's results.

Accident

Flight ULF48 took off from Mehrabad airport in Tehran at 08:20 GMT bound for New Jersey, via Madrid. There were 10 crew members and seven passengers on board. The aircraft climbed to flight level FL330, meaning roughly 33,000 feet (10,000 m). At take off, the aircraft's weight was 610,299 pounds (276,827 kg), including 254,600 pounds (115,500 kg) of fuel. The fuel was a mixture of type JP-4 and Jet-A. The aircraft's weight and centering were within required limits.

At 14:15, Flight 48 contacted the Madrid Air Route Traffic Control Center and reported that the estimated landing time would be 14:40. At 14:19, the Madrid ARTCC controller told the flight that they were identified on the radar screens and cleared the flight to descend to the CPL VOR via the Castejon radio beacon. At 14:22, the crew received the weather conditions at the airport; at 14:25, they were cleared to descend to FL100. The crew acknowledged and began descent.

A cyclone had passed over Spain earlier in the day, along with strong thunderstorms. However, visibility was good, and no dangerous weather alerts were issued by the weather service. At 14:30, the crew diverted to the left of their assigned route due to bad weather. At 14:32, the Madrid ARTCC controller cleared the flight to descend to 5,000 ft (1,500 m) and contact Madrid approach. At 14:33, the crew contacted Madrid approach and reported more bad weather ahead, subsequently requesting to deviate away from it.

The approach controller reported that he had established radar contact, and then asked the crew to confirm their instructions. The crew confirmed, and reported passing the Castejon radio beacon. The controller instructed them to maintain a heading of 260°. The crew acknowledged the transmission and reported their descent to 5,000 ft (1,500 m). This was the last transmission from Flight ULF48.

At the same time, south of the town of Valdemoro, locals noticed the aircraft flying at around 6,000 feet (1,800 m) on a 220° heading. The crew was aware that they were flying into poor weather conditions, but none of them expressed any concern until 14:34, when a crew member said, "We're in the soup!" Three seconds later, two witnesses on the ground reported seeing lightning strike the aircraft, followed by an explosion on the left wing near engine #1 (outer left). The left wing exploded into three large parts, and then disintegrated into 15 fragments.

At this time, the Flight Data Recorder stopped recording, but the Cockpit Voice Recorder continued to record. The autopilot disconnect warning was then heard. Unaware of the loss of the left wing, the crew tried to regain control of the crippled aircraft in vain. The aircraft dove rapidly and it crashed onto a farm at a height 3,000 feet (910 meters) above sea level at 14:35 (15:35 local time), 54 seconds after the moment of the lightning strike. All 17 people on board were killed and the aircraft was destroyed.

Investigation

The Imperial Iranian Air Force and the United States National Transportation Safety Board investigated the accident.

The Spanish government gave the Iranian government the primary responsibility to investigate, and the NTSB also successfully argued that it should help investigating as the aircraft type originated from the US.

It was established that a bolt of lightning struck the fuselage near the cockpit and exited the left wing's static discharger located at the wingtip. This created a spark in fuel tank number 1 (which contained 11,200 kg (24,700 lb) fuel), igniting fuel vapor in the tank. The blast wave from the explosion, at more than 80 psi (5.5 bar), caused the tank walls to collapse.

It is most likely that the ignition spark originated from an open circuit in a fuel valve's wiring. The explosion led to part of the wing trim separating and damage to the side members; as a result, the air flow deteriorated sharply and the wings began to bend significantly. As the flight was passing through an area of turbulence at high speed, the wing experienced major mechanical stress. The entire left wing separated just seconds later.

The NTSB could not determine if the wing separated due to the explosion or the stress.

Notes and References

Notes

Times are expressed in Greenwich Mean Time (GMT).

References

Ranter, Harro. "ASN Aircraft accident Boeing 747-131F 5-8104 Madrid". aviation-safety.net. Retrieved 2019-05-12.
"Iran Air Force 5-283 (Boeing 747 - MSN 19677)". Airfleets aviation. Retrieved 2019-02-01.
"5-283 Iran Air Force Boeing 747-100". Planespotters.net. Retrieved 2019-02-01.
^ "Special Investigation Report - Wing Failure of Boeing 747-131, Near Madrid, Spain, May 9, 1976" (PDF). National Transportation Safety Board. October 6, 1978. Retrieved May 12, 2019. - Copy at Embry-Riddle Aeronautical University.
"Crash of a Boeing 747-100 in Huete: 17 killed". Bureau of Aircraft Accidents Archives. Retrieved 2019-02-03.

External links

The accident aircraft

v t e Aviation accidents and incidents in Spain
Before 1970	Hubert Le Blon (April 1910) Aviaco SNCASE Languedoc crash (December 1958) Transair Douglas Dakota accident (August 1959) Iberia Flight 401 (May 1965)
1970s	Dan-Air Flight 1903 (July 1970) Iberia Flight 602 (January 1972) Scandinavian Airlines System Flight 130 (September 1972) Tenerife Spantax Convair CV-990 crash (December 1972) Aviaco Flight 118 (August 1973) Imperial Iranian Air Force Flight 48 (May 1976) Tenerife airport disaster (March 1977)
1980s	Dan-Air Flight 1008 (April 1980) Spantax Flight 995 (September 1982) Avianca Flight 011 (November 1983) Madrid runway disaster (December 1983) Iberia Flight 610 (February 1985)
1990s	Britannia Airways Flight 226A (September 1999)
2000s	Binter Mediterráneo Flight 8261 (August 2001) Flightline Flight 101 (October 2001) Spanair Flight 5022 (August 2008)
2010s	2015 Seville Airbus A400M crash (May 2015)

v t e Aviation accidents and incidents in 1976 (1976)
Jan 1 Middle East Airlines Flight 438Jan 3 Aeroflot Flight 2003Jan 15 Taxi Aereo el Venado Douglas DC-4 accidentFeb 9 Aeroflot Flight 3739Mar 6 Aeroflot Flight 909Apr 5 Alaska Airlines Flight 60Apr 26 Gubir shootdownApr 27 American Airlines Flight 625May 9 Imperial Iranian Air Force Flight 48May 15 Aeroflot Flight 1802May 23 Philippine Airlines Flight 116Jun 1 Aeroflot Flight 418Jun 4 Air Manila Flight 702Jun 6 Double Six CrashJun 27 Air France Flight 139Jul 28 ČSA Flight 001Aug 15 SAETA Flight 232Aug 23 EgyptAir Flight 321Sep 3 Venezuelan Air Force C-130 crashSep 9 Anapa mid-air collisionSep 10 Zagreb mid-air collisionSep 10 TWA Flight 355Sep 19 Turkish Airlines Flight 452Oct 6 Cubana de Aviación Flight 455Oct 12 Indian Airlines Flight 171Oct 13 LAB Boeing 707 crashNov 23 Olympic Airways Flight 830Nov 28 Aeroflot Flight 2415Dec 17 Aeroflot Flight N-36Dec 25 EgyptAir Flight 864
1975 ◄ ► 1977

Aviation accidents and incidents in 1976 (1976)

Jan 1 Middle East Airlines Flight 438Jan 3 Aeroflot Flight 2003Jan 15 Taxi Aereo el Venado Douglas DC-4 accidentFeb 9 Aeroflot Flight 3739Mar 6 Aeroflot Flight 909Apr 5 Alaska Airlines Flight 60Apr 26 Gubir shootdownApr 27 American Airlines Flight 625May 9 Imperial Iranian Air Force Flight 48May 15 Aeroflot Flight 1802May 23 Philippine Airlines Flight 116Jun 1 Aeroflot Flight 418Jun 4 Air Manila Flight 702Jun 6 Double Six CrashJun 27 Air France Flight 139Jul 28 ČSA Flight 001Aug 15 SAETA Flight 232Aug 23 EgyptAir Flight 321Sep 3 Venezuelan Air Force C-130 crashSep 9 Anapa mid-air collisionSep 10 Zagreb mid-air collisionSep 10 TWA Flight 355Sep 19 Turkish Airlines Flight 452Oct 6 Cubana de Aviación Flight 455Oct 12 Indian Airlines Flight 171Oct 13 LAB Boeing 707 crashNov 23 Olympic Airways Flight 830Nov 28 Aeroflot Flight 2415Dec 17 Aeroflot Flight N-36Dec 25 EgyptAir Flight 864

1975 ◄ ► 1977

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