Heathrow airport in London was Thursday disrupted by a major security alert after a man carrying a rucksack scaled the security fence and ran into the path of an aircraft on one of the airport's two runways.
Armed officers tackled the man as he ran towards a plane, dumping his bag as he was wrestled to the ground. The intruder would have had to scale a high perimeter fence, topped with barbed wire, to enter the security area. ( dpa )
The incident came a day before the planned opening of Heathrow's new Terminal 5 (T5) building by Queen Elizabeth II Friday.
Although police gave no indication as to the background of Thursday's security breach, one theory was that the man wanted to protest against the controversial expansion.
Scotland Yard said officers had carried out a controlled explosion on the rucksack but no explosives were found.
However, security analysts said the incident was "extraordinarily serious," as the intruder managed to get close to a plane on the airport's busy runways.
An aircraft was due to take off at the time but waited for the incident to pass, causing immediate tailbacks and delays, airport operators said.
Aviation security expert Chris Yates said Thursday that "serious questions" would have to be asked about how the man could have got so close to a plane carrying passengers.
"If there had been an explosive device, it could have been quite a disaster," he Yates.
Campaign groups Greenpeace and Plane Stupid, which have in the past staged protests against Heathrow's expansion, Thursday denied any involvement.
At the end of February, Greenpeace campaigners walked on to the runway at Heathrow and climbed on to the tail-fin of a BA Boeing to unfold a banner protesting against expansion.
A few days later, supporters of campaign group Plane Stupid scaled the roof of the Houses of Parliament in London, sending paper planes flying in protest against the controversial new terminal at Heathrow and plans to build a third runway.
The queen is due to open the "dream facility" new terminal, which cost 4.3 billion pounds (8.6 billion dollars) to build, at a lavish ceremony Friday.