This theory for the still unexplained disaster has emerged from investigations by attorneys acting for the victims' families in New York. If true, it raises serious concerns about the way in which aircraft not owned by airlines are able to avoid inspections ordered by the air safety authorities. It also serves to bring home the age of the TWA aircraft.
The lawyers have discovered that the plane was bought by TWA from Boeing in 1971 and sold to the Imperial Iranian Air Force, for use by the Shah, in 1975. The aircraft left the US for Iran on 15 December 1975.
A year later, on 14 December 1976, the aircraft was bought back by TWA. However, shortly before its sale to Iran, the Federal Aviation Authority issued a series of airworthiness directives for 747s. Lee Kreindler, from New York law firm Kreindler & Kreindler, maintains those checks were never applied because by the time they came into force the Boeing was sold to the Shah and was outside official control.
"They [the checks] would not have to be because it was not in the hands of an airline. My guys think nothing was done," said Mr Kreindler.
Nor, he claims, when the aircraft returned to commercial use with TWA, were the checks then enforced. "The mandate requires a full engine survey. This one was re-certified immediately, without a survey. It was stamped and approved in a day," said Mr Kreindler.
As further evidence for his claims that the Iranians failed to follow safety changes meted out to airlines, Mr Kreindler points to another Boeing 747 which exploded near Madrid on 9 May 1976, killing 15 passengers. The aircraft, which had been converted into a freighter, was also owned by the Imperial Iranian Air Force and was on a military flight. According to an official accident report, "Witnesses observed lightning strike the aircraft followed by fire, explosion and separation of the left wing".
Mr Kreindler believes the coincidence of two Boeing 747s, both of which once belonged to the Iranians exploding in mid-air, albeit years apart, is remarkable. If nothing else, he claims, it shows that some 747s were prone to explosion.
Despite the witnesses' claim to have seen lightning hit the aircraft, accident investigators were unable to establish for certain the cause of the disaster. In their report, they said that "one hypothesis is that an explosion in a fuel tank destroyed the left wing and that lightning- strike currents ignited the explosion". But, the investigators went on: "Another credible hypothesis is that severe turbulence was encountered which caused the wing to fail as a result of structural overloads." They were at a loss to say for definite why the fuel tank was so vulnerable to lightning.
The Madrid disaster, argues Mr Kreindler, shows the Iranians had not heeded the mandate issued to airlines in 1975.
US investigators appear to be no nearer determining the cause of the Long Island explosion. Meanwhile, in the absence of an explanation, Mr Kreindler, who represents the relatives of 49 of those on board, has launched a law-suit against TWA. The first, preliminary hearing in what promises to be a protracted case, took place in Manhattan two days ago.
Mr Kreindler pooh-poohs the idea of bomb or missile, claiming there is no firm evidence to support either theory. The fault, claims Mr Kreindler, lies with TWA for failing to pursue the necessary safety and maintenance checks.
This is hotly disputed by the airline. John MacDonald, TWA's public affairs chief, described Mr Kreindler's law suit as "baseless". His airline's plane, said Mr MacDonald, "met all the applicable airworthiness directives and all the safety standards at the time it left JFK".
For 21 years after it was returned to TWA, the aircraft had flown without incident, Mr MacDonald pointed out: "That is a very impressive safety record for that aircraft."
The lawsuit also implied a mechanical failure. In fact, admitted Mr MacDonald, "we are no nearer knowing what happened. If we were, Mr Kreindler would not have a law suit".