Privacy concerns raised after US air marshals revealed to be secretly shadowing passengers

Thousands of airline passengers have been subjected to discreet observation by armed US air marshals under a programme called “Quiet Skies”.

The existence of the programme was disclosed by the Boston Globe, triggering complaints that passengers’ civil liberties were being compromised.

This was emphatically denied by the Transportation Security Administration (TSA), which insisted that the programme was purely intended to head off any threat faced by the travelling public.

The programme, which was first established in 2010 and updated in 2012, was designed to prevent a repetition of the September 11 atrocities when four domestic US flights were hijacked.

Two planes were flown into the Twin Towers in New York, a third plummeted into the Pentagon in Washington and a fourth crashed before reaching its target. Nearly 3,000 people were killed.

“This is observation, not surveillance,” Michael Bilello, an assistant administrator at the TSA, told the Telegraph.

“We are looking for people with a unique pattern of travel, but that is not enough on its own to be put into the programme. There has to be a review by legal and privacy experts as well.

“We are observing where we believe there could be a threat to aviation, aircrew and passengers. This is mitigation. There are many people who are not on any list or any other programme and the threat can come out of the blue.

Michael Bilello, assistant administrator at the TSA

“Our aim is to prevent anything happening at 30,000 feet and if the person does not do anything, that is considered a successful mission as well. This is a modern approach based on a targeted risk, but ordinary law-abiding citizens are not the subject of this programme. Race and religion do not come into this - there is no racial or religious profiling.”

Many of the operational details of the programme are still unclear. It appears that there are several levels of screening employed to identify passengers who could pose a potential threat. The first sift is understood to be based on previous travel patterns followed by other checks, details of which have not been disclosed.

Should the passenger be worth observing, an air marshal is assigned to shadow the person involved both at the airport and on the flight.

Marshals then work from a behaviour checklist which includes observing whether subjects appeared to be abnormally aware of the surroundings, suggesting they were scanning the area for security personnel.

Other triggers include passengers changing their appearance - such as shaving off a beard - before boarding the aircraft or displaying nervousness, such as by sweating profusely.

The US is not alone in looking at sophisticated techniques for identifying potential threats. The EU also piloted a four-year study, which was completed in 2008, examining how security cameras could - with the aid of sophisticated computer software - be used to identify suspicious passenger behaviour at airports.

At a glance | How to spot a terrorist, according to US airport security

According to the Boston Globe, about 35 passengers are observed every day under the US programme.

Defenders of the programme believe it is an effective use of the limited number of available air marshals.

The Senate Commerce Committee was briefed by the TSA on how the programme was being implemented. Committee members are understood to have been reassured that potential targets for observation are chosen on the basis of not only their travel patterns but also other intelligence.

But privacy campaigners have questioned its legality and its effectiveness was questioned by Bob Mann, a New York-based aviation consultant.

He said the work was similar to that employed in Israel, but voiced doubts whether TSA had the resources to carry it out as effectively.

“I think the air marshal service is a function looking for an objective,” he said. “This may be mission creep.”

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