British and American intelligence agencies developed the capabilities to spy on mobile phones used on commercial flights to avoid "a new September 11".
Since Edward Snowden's disclosures in 2013, it has been well established that the National Security Agency (NSA) and its British equivalent, the Government Communications Headquarters (GCHQ), have spied on mobile phones, but new revelations show the agencies are now able to do so at 33,000ft and above.
And regardless of whether phones are in flight-safe mode, simply having them on is enough for the agencies to collect data from the phones at "near real time", according to internal documents seen by Le Monde.
The capabilities garnered so much enthusiasm from spy agencies that an internal newsletter describing the project said: "Heaven may belong to the NSA."
From documents leaked by Snowden to Le Monde and The Intercept, the capability was developed as early as 2005 and a 13-page document titled "tracking civilian aircraft the world over" detailed how the technology would be used to prevent another 9/11 tragedy.
The document also shows that some airlines were more susceptible to be spied on than others, based on the likelihood the Central Intelligence Agency (CIA) believed they were being used by terrorists.
One document reads: "The CIA believes that Air France and Air Mexico are potential targets of terrorists," adding that, there is no legal problem to target airplanes of both companies abroad" and that they "should be under the highest supervision as soon as they enter US airspace".
The technology was not simply reserved to terrorists, however.
Israeli Prime Minister Benjamin Netanyahu, the head of the World Trade Organization and CEOs of major companies were all targeted by the NSA and GCHQ, the leaks show.
One NSA document from 2003 joked: "What do the President of Pakistan, a trafficker of cigars or weapons, a terrorist and the member of a nuclear proliferation network all have in common? They all use their mobile phones while on a plane."
A GCHQ spokesman said: "We do not comment on matters related to intelligence.
"However, our work is conducted in accordance with strict legal and policy framework that ensures that our activities are authorised, necessary and proportionate, and that a rigorous control to be made by the Secretary of State, the parliamentary committee intelligence and security as well as the regulatory authority for interceptions and intelligence.
"Moreover, the legal regime of interceptions practiced by the United Kingdom fully respect the European Convention on Human Rights."
A spokesman for the NSA said: "[Our] intelligence activities are in full compliance with the legal and policy framework in force."