They must also be easy to use, take up little space and provide quick results, says Chris Yates, a security expert with Jane's Airport Review.

ECONOMIST: Airport screening technology

Air traffic control personnel "would have known immediately" of a crisis when the planes veered away from their normal route, according to Chris Yates, aviation security editor of Jane's Defence Weekly.

BBC: Cockpit drama of doomed planes

Chris Yates, an aviation security expert, told CNN it was likely there would be questions about whether the helicopter that crashed should have been flying, given the poor visibility Wednesday morning.

CNN: London helicopter crash prompts safety questions

Finnigan, 33, will be assisted by captain Chris McPhee following the departure of Mark Yates.

BBC: Finnigan takes over as Kidderminster temporary boss.

Chris Bryant MP claimed in a Commons debate two weeks ago that Mr Yates, had misled the Home Affairs Committee last September when he said only 10 to 12 people had had their mobile phone messages intercepted.

BBC: Culture, Media and Sport Committee