An Iraq-bound US air force cargo plane carrying almost 60 tonnes of "hazardous" gas cylinders was forced to make an emergency landing at Shannon airport yesterday.
Hundreds of employees working in a business park next to the airport were evacuated, and gardaí blocked vehicular access to the area amid fears that the plane could overshoot the runway.
The Boeing C17 Globemaster III had been carrying five crew and 38 compressed helium gas cylinders for use in security observation balloons in Iraq. Normally located at McChord air force base in Washington, it was en route from Kansas to an RAF base in Mildenhall in England.
At around 7am, the pilot reported a problem with the aircraft's hydraulic system, which could have resulted in brake failure, leaving the jet with only the reverse thrust of its engines to stop.
After informing Air Traffic Control at Shannon of the problem, the plane circled over the sea for about two hours to burn off excess fuel before landing amid fears that the weight of the cargo on board would cause the plane to overshoot the runway.
The plane landed safely, however, the brakes seemingly unaffected by the hydraulics problem.
In a statement, the US embassy in Dublin said the aircraft had sought to land at Shannon as the Mildenhall runway was not long enough to ensure a safe landing.
At 3,200 metres (10,500ft), the Co Clare runway is the longest in Ireland, and a regular host to emergency landings by troubled transatlantic flights.
However, emergency services described yesterday's incident as one of the most serious in recent times. Coast Guard services were on standby, along with gardaí, paramedics, and firefighting crews.
One Coast Guard source said: "We were told in no uncertain terms to head for the Shannon Estuary because if there was going to be a crash it would not be land based, it would be in the estuary or the sea."
Another rescue worker said: "This was the hairiest one in a long time. I think we were all prepared for the worst knowing that there was a serious risk the plane would overshoot the runway. There was also talk of the plane ditching in the estuary."
In its statement, the US embassy expressed its thanks to the staff and emergency response team at Shannon airport for their "quick action" in support of this emergency landing.
It said the gas carried on board was used in "radar balloons of the type that have been used by law enforcement agencies in the United States for many years.
"While this cargo is technically considered 'hazardous', it is non-flammable, commonly used in consumer applications [eg, birthday party balloons], and transported in accordance with international safety regulations."
The statement continued that, pursuant to UN security council resolutions, "this cargo is in transit to the multinational forces in Iraq operating at the request of the interim government of Iraq.
"Its transit through Shannon airport, as is the case with all other traffic supporting the multinational forces in Iraq, is in compliance with Resolution 1546, Section 15, which calls on all UN member states 'to contribute assistance to the multinational forces, including military forces, as agreed with the government of Iraq'."
A spokesman for the Department of Foreign Affairs said the American embassy had contacted it in the "immediate aftermath" of the landing to request retrospective permission to land - which was granted. He said in the short time available the embassy had been unable to request permission to land beforehand.
A spokeswoman for the Department of Transport said its Air Accident Investigation Unit had asked to speak to the crew of the aircraft to determine what happened.