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Wednesday, July 24, 1996 - Page updated at 12:00 AM

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Corrected version

Twa 747 Wasn't First To Explode In Midair -- Twenty Years Ago, Iranian Freighter Crashed In Spain

Seattle Times Aerospace Reporter

The crash of TWA Flight 800 was not the first time witnesses on the ground watched as a Boeing 747 burst into flames and tumbled to Earth.

In the week since the TWA crash, many commentators, from retired investigators to academic safety experts, have publicly said there was no precedent for a 747 exploding into flames in flight. That has led to speculation of a terrorist bomb in the TWA case.

But twenty years ago, in a crash that drew little public attention, a former Continental Airlines 747-100, converted into a freighter for the Iranian air force, exploded in flight near Madrid, Spain.

As the jet descended into Madrid in a heavy rainstorm on May 9, 1976, witnesses reported it caught fire and exploded, losing its left wing as it careened to Earth. All 17 on board were killed, including four Tehran-based Boeing employees on the flight.

U.S. aviation authorities studied the Madrid crash but were unable to pinpoint a cause.

The authorities suspected, but never officially concluded, that either a spark from an electrically driven valve or a bolt of lightning touched off a fiery explosion that ripped apart the plane's wing.

The scenario most widely considered was that leaking jet fuel had accumulated and mixed with air inside a "dry bay" section of the wing, above the engine, to create a highly combustible vapor.

Boeing has since strengthened the sealants in the dry bays of 747s to prevent leaks.

There are no known parallels between the Madrid and TWA crashes. All that's known by investigators, still in the early stages of retrieving and analyzing wreckage, is that the TWA jet exploded into a ball of flames last week off Long Island, N.Y., as the result of a bomb, a missile or catastrophic mechanical failure.

Thus far, they have found no traces of explosives on the wreckage recovered from the waters off Long Island.

Boeing spokesman Doug Webb had no specific information about the Madrid crash that might be applicable to the TWA tragedy, which killed all 230 on board. "At this point, we're looking at every possibility," Webb said this morning.

Bob Barlett, spokesman for the National Transportation Safety Board, said investigators continue to concentrate on retrieving perishable evidence, but intend to "review the history of all similar cases," including the Madrid crash, in due course.

In the Madrid case, the left wing landed some distance from the main wreckage, its skin torn off in a pattern indicating an explosion ignited inside the wing.

Another theory investigators postulated but never proved in the Madrid case held that an unusual gust of wind or turbulence overloaded the wing.

The Madrid crash had ramifications in the United States.

After the U.S. Air Force found fuel had leaked into the wing dry bay areas of the two 747s it then operated, the Federal Aviation Administration in late June 1976 ordered all 747 operators to immediately inspect for fuel leaks in the wing dry bay and engine strut, Aviation Week & Space Technology, a respected industry trade magazine, reported at the time.

Most found leaks, the magazine reported.

----------------------- 747-100 wing fuel tanks -----------------------

All the fuel on a 747-100 is stored in wing tanks. In a 1976 crash, investigators hypothesized that fuel could have leaked into a sealed cavity above one of the engines, called a dry bay, creating a combustible vapor that ignited.

Dry bay: An empty, sealed compartment located inside the wing and directly above the engines, adjacent to wing fuel tanks.

Fuel tanks: Jet-wing compartments store thousands of gallons of jet fuel.

Published Correction Date: 07/27/96 - The Iranian Air Force 747- 100 That Exploded And Crashed Near Madrid On May 9, 1976, Was Purchased From Twa. This Story Incorrectly Identified The Original Owner As Continental Airlines.

Copyright (c) 1996 Seattle Times Company, All Rights Reserved.

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