Published on July 20th, 2018 | by FII Reader0
Tuskar Rock – The tragic story of Irish 712
Fifty years ago Ireland was plunged into mourning when an Aer Lingus Viscount plunged into the sea off Tuskar in Co. Wexford. At the time Michael McRitchie had just qualified as a UK licensed engineer and researched the tragedy after his examiner told him about an accident in Hong Kong which might yet be a clue to the disaster. This article was written for a Belfast newspaper eight years after the incident.
DRIVER Cheung Ho Lee gave an awed whistle as he drove his catering truck across the Hong Kong apron. It was the mini-skirt era, and walking from an aircraft was a breathtaking vision in the shortest skirt he had ever seen. His eyes were still on her long suntanned legs when his truck roof ploughed into the tail of a Viscount airliner.
As ex-driver Lee left to seek employment elsewhere, engineers began inspecting the damaged Viscount. What they found when they cut into the damaged tail could explain the unsolved mystery of its sister aircraft Oscar Mike, the wreckage of which still rests 10,000 miles away below the Irish Sea.
The Vickers Viscount was one of the world’s safest airliners, and Aer Lingus was (and is, 50 years later) one of the world’s safest airlines. Yet to this day nobody knows why Oscar Mike and its 61 occupants should descend into the sea without even a distress call.
The theories have been as wild as they have been many. Some suspected a bomb on board, while a rumour that the aircraft had been downed by a missile fired from a military range became so strong that London issued an official denial. But one of the most plausible explanations was given to me by an aircraft engineer and surveyor who spent many years in the Far East before joining the Air Registration Board, later to become the UK Civil Aviation Authority.
The tragic story of Irish 712 began at Cork at 1130 on March 24, 1968, when Captain Barney O’Beirne (35) set his aircraft rolling for the hour and a half trip to London. The weather was clear and calm and by 1157 they were cruising at FL170 en route Strumble. Flight crew Ann Kelly and Mary Coughlan were serving coffee as Capt. O’Beirne cleared Irish airspace. “Irish 712 clear contact London Airways on 131.2”, said the Shannon controller, “good day”.
In the London centre Irish 712 was represented by a card strip in front of the controller, who was waiting for the handover call. But the call which he received at 1158 was far from the routine message he expected.
“Twelve thousand feet, descending, spinning rapidly”, said the calm voice from the cockpit. Then the transmission became garbled and may have been meant for 22-year-old First Officer Paul Heffernan. “we moved … breaking up … that’s better … who are you talking to?” There was a brief crackle of static, and silence.
Another Viscount was diverted to 712’s last known position to search from 500ft, but the crew saw nothing. Rosslare lifeboat was launched, an RAF Shackleton took off from Ballykelly and shipping was alerted, but it was next day before the Royal Navy frigate HMS Hardy found nine bodies along the aircraft’s flight path. Five more were recovered later, post-mortems revealing that all had died as a result of impact.
Then a huge salvage operation began and divers, setting up endurance records in their search for the wreckage, located a 23ft section of the fuselage on the sea bed 275 ft down. In June it was raised by the Royal Navy salvage ship HMS Reclaim and after many hours’ lifting it was within a few yards of the deck, with passengers’ bodies visible in their seats, when it slipped and disappeared forever beneath the waves.
The accident report was issued two years later, concluding that “there is not enough evidence available to reach a conclusion of reasonable probability as to the actual cause of this accident. The probable cause of the final impact was impairment of the controllability of the aircraft in the fore and aft (pitching) plane.”
So what had happened? As well as Capt. O’Beirne’s report that his aircraft was spinning, many people reported seeing it flying low across the Irish Sea. Two had seen it crash into the sea “like a waterspout”. They timed the crash at 1210, some 12 minutes after the pilot’s report on the radio. The discrepancy could have been the time taken for the aircraft to spin from 17,000 ft to the surface. It’s a long time to spin, and the scene inside the cabin can only be imagined.
Information on the behaviour of such large aircraft in extreme situations is sparse, but a wartime bomber pilot told me that his Lancaster, about the size of a Viscount, spun down at about 2500 fpm after being hit in the tail over Essen. He and two of his crew, pinned to the sides by the spin, escaped by parachute when the aircraft broke up around them. Shorts test pilot at the time, Don Wright, told me he thought that a machine of this size would descend at about 4000 fpm, but if the spin was stable or some control had been retained the descent could be much slower.
The victims’ bodies bore no trace of explosion or fire. In fact seat cushions smelt of fuel, which would have been consumed had the wreck been ablaze. Had there been engine failure the captain would have said so; the only thing that could have caused him to lose control was catastrophic failure of the airframe.
By 1968 the problems of metal fatigue and pressurisation were well known following the Comet disasters of the 1950s. The Viscount never had such troubles. It built up a brilliant record and was well liked by crews and passengers alike.
But now comes the link between the Wexford tragedy and Driver Lee’s encounter with the parked Viscount. The engineers inspecting the damage found hidden corrosion at the rear of the pressure cabin – corrosion which might not have been found in normal inspection procedures. The machine had seen extensive service in the Dutch East Indies, and it was concluded that high humidity and tropical conditions had been a factor in the corrosion. The aircraft was scrapped.
The Aer Lingus Viscount, EI-AOM, had been bought from KLM in 1967 but I could not determine whether KLM had used it on its East Indies short-haul services. Had the rear of the pressure cabin failed due to corrosion, the metal would have burst outwards, severing or jamming vital controls. The tail could have broken off. Engine torque would have caused the aircraft to spin, and the pilots could do nothing to recover.
Aer Lingus spokesman at the time, Capt. Jack Millar, was interested in the theory and put it to his colleagues. “We are still a small enough airline for everybody to know everybody else, and the loss is still deeply felt. None of us will ever forget that dreadful time”, he said. After the accident every Viscount had been grounded for inspection, but all were perfect.
Technical chief at the time, Dick White, told me he was confident that any sign of corrosion in the pressure hull would have been picked up during normal inspection programmes. “No such corrosion was ever found in the Aer Lingus fleet either before or after the accident. “BAC, which made the aircraft, have had no problems with the Viscount pressure bulkhead”.
Yet the rumours persisted. The Viscount had been brought down by a stray missile fired from the Aberporth testing grounds even though they were closed at the time. Or it was hit by a target drone from another test area, and the UK Government had covered up the missile launch. Or it had collided with a second aircraft. So in 2000, the Irish Minister for Public Enterprise commissioned a review of the accident, followed by an independent report from an International Study Team which published its findings in December 2001.
After reviewing witness statements the team concluded that the Viscount crew had recovered from the initial spin at about 1000ft and by brilliant airmanship had kept their damaged aircraft in flight for half an hour before finally losing control. Because of the missing tailplane they could only control pitch by using full power, so could not descend to land or ditch without losing all control. They further concluded that:
- An initial event, which cannot be clearly identified, disturbed the air flow around the horizontal tail surfaces and the pitch control of the aircraft. In the light of what was observed by non-skilled people there was a strong indication that structural fatigue, flutter, corrosion or bird strike could have been involved.
- It is possible that the sensitivity of the engine fuel control units to negative accelerations imposed during the initial upset, had an adverse effect on the subsequent flight path of the aircraft.
- The severe manoeuvres of the aircraft following the initial upset and the subsequent flight would have been outside the airworthiness certification envelope and may have resulted in some deformation of the structure.
- A number of possible causes for an impairment of pitch control were examined and it is considered very possible that excessive spring tab free play resulted in the fatigue failure of a component in the tab operating mechanism thus inducing a tailplane-elevator tab free flutter condition.
- The loads induced by the flutter condition would be of sufficient magnitude and frequency to cause a fatigue failure of the port tailplane within the timescale estimated for EI-AOM.
- There was no involvement of any other aircraft or missile.
Today the disaster is remembered in a memorial garden in Rosslare village. Half a century on, I still wonder about that chance discovery of corrosion following the apron accident in Hong Kong, although it seems that excess play in a control linkage may well have led to elevator flutter and the subsequent disaster. Sadly, it seems that there will never be closure for the relatives of those lost on Irish 712.
By Michael McRitchie