Records from an inspection of the Aer Lingus Viscount St Phelim, carried out three months before it crashed killing all 61 people on board, went missing soon after the maintenance check in December 1967.
It was the penultimate full inspection of the aircraft, and although a routine inspection was again carried out in early March 1968 - only two weeks before the crash - it is not known whether defects identified in December were specifically addressed.
But the 1970 report into the crash at Tuskar Rock made no reference to the missing documents, a circumstance which the Minister for Public Enterprise said "deeply disturbed" her, as she presented the findings yesterday of a review by Irish and British civil servants of all files held on the accident.
In a damning series of conclusions, Ms O'Rourke's departmental investigators said it was "difficult to comprehend" the omission from the original report of details of the aircraft's maintenance history, "except in the briefest terms".
They had the same difficulty understanding the total omission from the 1970 findings of "serious errors", originating within Aer Lingus, in the St Phelim's maintenance operating plan. Most damning of all was the fact that the aircraft's maintenance history was extensively investigated by Aer Lingus after the crash, but Ms O'Rourke's investigators found it "difficult if not impossible to understand" why none of this research was included in the 1970 report.
The review concedes there is no evidence that the St Phelim's maintenance history was a factor in the accident. But it also concludes it was "unsatisfactory" that the official of the old Department of Transport and Power who approved the aircraft's certificate of airworthiness in early 1968 was also responsible for the investigation of the subsequent crash.
The official in question, aeronautical officer Mr R.W. O'Sullivan, died earlier this year aged 95. He was interviewed by the Department of Public Enterprise investigating team, but had no recollection of events surrounding the inspections of December 1967 and March 1968.
Presenting the findings, Ms O'Rourke said people reading it would be "concerned that the arrangements of the time were such that those who regulated the safety procedures of airlines were also entrusted with investigating accidents". This was the "norm" then, she added, but since the establishment of the Irish Aviation Authority and the separate Air Accident Investigation Unit in the early 1990s, such conflicts of interest no longer existed.
The departmental review also places the missing 1967 documents in a historical context - one of generally poor record-keeping in the Aer Lingus of the 1960s. The loss of the St Phelim paperwork was "not the first such occurrence", it found, noting that "the employment of maintenance personnel from a non-aviation background was perceived as an important factor".
While the loss of the records was a matter for concern, the review concludes: "The available evidence is that these errors were by no means unique to EI-AOM [the St Phelim]. There is evidence that there were significant failures in these areas within Aer Lingus at the time, and that these were not being detected by the Department.
"However, it must be noted that this was in the days before computerisation, and it is generally accepted that the problems experienced in Aer Lingus were widespread within the international aviation industry at the time."
The February 1968 renewal by Department of Transport and Power officials of the St Phelim's Certificate of Airworthiness (C of A) was on the basis of an inspection of maintenance paperwork rather than a physical inspection of the aircraft, according to evidence given by surviving officials.
But the review's authors found that since a full check of paperwork should have revealed documents were missing from December 1967, and as the March inspection was yet to be carried out, the gap in the maintenance record would have been a cause of concern for those certifying airworthiness. They envisaged three possible scenarios to explain the decision to renew the C of A. One was that the Department authorities noticed the paperwork missing but were satisfied the December inspection had been carried out and decided not to comment (this would be "most unusual", the authors say).
The second theory is that they noticed the missing documentation and called for a repeat of the December check.
The third possibility, which the review finds most likely, is that the missing paperwork was not noticed by officials prior to the renewal of the C of A, "or even prior to the accident". But this is in conflict with the recollections of one of the Department officials involved.
Finally, referring to the possibility raised by the 1970 report that a mid-air impact with an object such as a missile or an RAF aircraft might have precipitated the crash, the review notes that the position of the UK has not changed. The British authorities still say there were no naval or military exercises in the area where the plane went down; missile ranges were closed at the time of the flight; no missile fragments trawled by fishermen at or near Tuskar Rock have been connected with the St Phelim; and there was no loss of any UK military or civil aircraft on March 24th, 1968.