Did British missile hit Flight 712?

For three decades Ireland's conspiracy theorists have dissected the mystery of Aer Lingus Flight 712, which inexplicably plunged into the Irish Sea from 17,000 ft on a fine spring day, killing all 61 passengers and crew.

Tomorrow, Mary O'Rourke, the republic's enterprise minister, will re-open the case of the 1968 disaster when she meets the outgoing British ambassador to Dublin, Dame Veronica Sutherland. Ms O'Rourke now believes there was no aircraft failure, once more fuelling speculation that a British missile or target drone downed the plane.

At that time, the Ministry of Defence tested surface-to-air missiles over the Irish Sea, firing at pilotless aircraft, but denies involvement.

Victims' relatives banded together last year to find the truth. Jerome McCormack, aged 51, a Cork chef, who lost his brother, Neil, 35, said: "We need to lift the embargo of silence so those in the know are allowed to speak freely. We are not looking for anyone to be hanged. We just want to know what happened."

The St Phelim, a Vickers Viscount, crashed off the Wexford coast just after noon on Sunday, March 24, 1968, en route from Cork to Heathrow. Its penultimate, garbled message indicated another aircraft was in the area. In its last message, eight seconds later, co-pilot Paul Heffernan, aged 22, said: "12,000 ft descending, spinning rapidly."

Witnesses say Captain Barney O'Beirne, aged 35, managed to level the four-engine plane about 1,000 ft above the water, and flew on for about 15 minutes before it crashed close to Tuskar Rock. There was no black box recorder on the aircraft, which had undergone a major inspection three weeks earlier.

A paragraph in investigator Richard O'Sullivan's report is responsible for much of the speculation. He noted: "The conclusion that there was another aircraft involved is inescapable. No aircraft have been reported missing, but there remained the possibility that an unmarked aircraft, either a drone aircraft target or a missile, might have been there."

The most popular theory is that the St Phelim was hit by a rogue missile fired from the Royal Aircraft Establishment's range at Aberporth in Dyfed, then Britain's most advanced missile testing station. The MoD says the range was closed on Sundays. However, RTE, the state broadcaster, last year found inconsistencies in log books, and suggested testing could have taken place that day.

A second theory suggests that because a special radar transponder on the St Phelim failed, a British warship conducting exercises in the area, HMS Penelope, mistook the aircraft for a target drone. The MoD says no ships were close enough. But it admits that the logbooks of two of the five vessels in the vicinity are missing. It has never provided the logs of the others, including HMS Penelope, because the Irish government did not ask for them.

Another version is that the St Phelim may have been struck by a pilotless drone. Several witnesses described an aircraft with red wings close to the plane's last reported position.

The RAF then used de-commissioned Meteor jets for target practice, and the remains of one were discovered off Tuskar Rock in 1974. Fishermen ridicule RAF claims that the wreckage floated there, saying currents and tides make that impossible.

Whatever brought the St Phelim down, local people puzzle over the search operation, which was led by the Royal Navy. It took 70 days to find the wreckage, despite several reports which pinpointed where it was finally discovered. A local trawlerman, Billy Bates, found it on his first visit there. He says the navy had told him it had looked there three times already.

The search team on HMS Reclaim then tried to raise the fuselage without using a steel net. It scattered as it broke the surface and sunk to the seabed. With it went many of the victims, and any chance of discovering what had happened.

Ms O'Rourke said: "The RTE programme was vivid, and the evidence put forward did not find an echo in the records here. I remain open if there is new evidence to push further on this issue. It is an unexplained mystery."