An emergency on a cargo plane alarmed residents of Askeaton, Co Limerick, who reported “loud bangs and flames” and contacted gardaí to report an aircraft in trouble.
The serious incident took place on March 28th last year when the US-registered McDonnell Douglas DC8 suffered engine stalls shortly after take-off. The crew was forced to shut down two of the engines and to return to Shannon.
There were four crew members on board the 40-year-old aircraft, which was carrying 34,911lbs of "clothing and personal belongings".
The incident received media attention at the time after anti-war campaigners claimed it was carrying material for US military use.
At the time, the operators declined to say what was on board the flight but confirmed it was licensed to carry ammunition, as well as depleted uranium and that the US military was one of its customers.
A final report by the Air Accident Investigation Unit (AAIU) of the Department of Transport published today said the probable cause of the emergency was rapid icing of the engines. No damage to the engines was found when the aircraft was inspected afterwards.
Accident inspector Paddy Judge commended the air traffic controller at Shannon airport who brought the plane down safely after it declared an emergency and was forced to turn back shortly after it took off for Qatar 10.30pm.
Mr Judge said when the controller “realised the developing serious situation” he directed the aircraft directly to runway 6 at Shannon, an area clear of obstacles. This decision was “clear thinking and correct”, Mr Judge said in his report.
“If the situation had deteriorated further this decision offered the best possibility of an optimum outcome. The investigation therefore commends the approach controller on his quick thinking and the clarity of his instruction during this emergency situation.”
The pilot’s decision to descend rapidly in order to pick up speed and maintain control of the aircraft had initially caused “significant and justifiable” concern to the air traffic controllers, who were not informed of the reason for the sudden descent because "the efforts of the flight crew were directed towards retaining control of their aircraft", the report said.
“Although local residents may also have been concerned due to the loud bangs and flames seen coming from the aircraft nevertheless the minimum altitude recorded during the occurrence was 1,100 ft."
The pilot landed the aircraft with all four engines operating normally.
After the incident, the operator wrote to all flight crew informing them of the incident and that rapid icing of the engine inlets was the most likely cause.
The operator also implemented a flight operations policy “to strongly encourage the use of engine anti-ice for departures when icing conditions are in any way suspect and the temperature is below 10ºC”.
If performance [was] limited then the new procedure “strongly encourages the use of the engine anti-ice after completion of the second segment climb at 400 feet”.
The AAIU inspector did not make any safety recommendations.
In line with its usual procedure, the AAIU did not identify the operator of the aircraft involved in the emergency and declined to do so when asked.
The flight was operated by US-based Murray Air, which confirmed after the incident last year that it is licensed to carry explosives, armaments and other munitions. A spokeswoman for the firm confirmed the licence included the carriage of depleted uranium.
"It's an insurance-based licence. We are insured to do so, we are therefore licensed to do so. That does not necessarily imply that we have used the licence to transport uranium," she said.