US secretary of homeland security John Kelly has defended the decision to allow personal electronic devices to be transported in aircraft holds despite being considered a potential threat within the passenger cabin.

Kelly addressed the apparent contradiction in remarks to the recent Aspen Security Forum in Colorado on 19 July.

The US ban – which has since been lifted against the airports concerned – prevented passengers from carrying large electronic devices, such as laptop computers, on board, but nevertheless allowed them to be stored in the hold.

Kelly indicated that the nature of the threat which triggered the measures would have required direct access to the device affected.

"The threat would indicate, at this point, that there was no possibility of remote detonation," he said.

Kelly gave further details of the reasoning behind the electronics ban, stating that – after he took over in January – he was briefed on a "very sophisticated" emerging threat.

"It was not only sophisticated but it was real, and it was targeted at certain airports," he said.

The US Transportation Security Administration, which is responsible for passenger screening at airports, built two devices to test.

"Having been around explosions all my life, the device, as it was described to me, had an amount of explosive on it that I just did not believe could destroy an airplane in flight," says Kelly, who served with the US Marine Corps before his appointment to head the Department of Homeland Security.

"We tested it on a real airplane on the ground, pressurised, and – to say the least – it destroyed the airplane," he says.

"We didn't feel at the time that overseas airports had the kind of security initially that could give me comfort that they could detect this device."

Under a ban imposed in March, passengers on US-bound services from 10 airports were prohibited from taking large electronic devices into the cabin.

While the restriction affecting these airports has since been lifted, following enhancement of security measures, Kelly insists there has been "no compromise".

"I am reasonably confident that we can detect the devices, given all of the things that we are requiring people to [do]," he says.

"But, again, I can't emphasis enough – there are people out there, very smart people, very sophisticated people who do nothing but [try] to figure out how to blow up an airplane in flight."

Kelly views computer tomography technology as the "next thing" to counter the threat from explosives. Computer tomography scanners have been certified by the US FAA for more than two decades.

"The technology generally already exists," he says. "We just have to now start purchasing it."

Kelly stresses that US authorities are "not mandating" such equipment, but he says that airports and airlines without the capability will not be able to operate services to the USA unless they impose a restriction on large electronic devices.

Source: Cirium Dashboard