Flight security expert Chris Roberts says he was pulled off a United Airlines flight for exposing safety flaws in airline entertainment systems. Courtesy: Fox News

Flight security expert Chris Roberts says he was pulled off a United Airlines flight for exposing safety flaws in airline entertainment systems. Courtesy: Fox News

UNITED Airlines stopped a prominent security researcher from boarding a California-bound flight late on Saturday, following a social media post by the researcher days earlier suggesting the airline’s on-board systems could be hacked.

Chris Roberts attempted to board a United flight from Colorado to San Francisco to speak at a major security conference there this week, but was stopped by the airline’s corporate security at the gate.

Roberts founded One World Labs, which tries to discover security risks before they are exploited.

Roberts had been removed from a United flight on Wednesday by the FBI after landing in Syracuse, New York, and was questioned for four hours after jokingly suggesting on Twitter he could get the oxygen masks on the plane to deploy.

Find myself on a 737/800, lets see Box-IFE-ICE-SATCOM, ? Shall we start playing with EICAS messages? "PASS OXYGEN ON" Anyone ? :) — Chris Roberts (@Sidragon1) April 15, 2015

EICAS is an integrated engine-indicating and crew-alerting system used in aircraft to provide crews with engine and other systems instrumentation, such as temperature values, fuel flow and quantity and oil pressure.

Authorities also seized Roberts’ laptop and other electronics, although his lawyer says he hasn’t seen a search warrant.

Bye bye electronics, all encrypted....and all now in custody/seized pic.twitter.com/a5o6rYTbZ0 — Chris Roberts (@Sidragon1) April 16, 2015

A lawyer for Roberts said United gave him no detailed explanation why he wasn’t allowed on the plane, saying instead the airline would be sending Roberts a letter within two weeks stating why they wouldn’t let him fly on their aircraft.

“Given Mr Roberts’ claims regarding manipulating aircraft systems, we’ve decided it’s in the best interest of our customers and crew members that he not be allowed to fly United,” airline spokesman Rahsaan Johnson told The Associated Press.

“However, we are confident our flight control systems could not be accessed through techniques he described.”

When asked what threat Roberts posed if United’s systems couldn’t be compromised, Johnson said: “We made this decision because Mr. Roberts has made comments about having tampered with aircraft equipment, which is a violation of United policy and something customers and crews shouldn’t have to deal with.”

Johnson said the airline reached Roberts several hours before his flight to tell him he couldn’t fly.

Hahaha!! Well United, let me tell you about my trip and the new friends I made :-)) pic.twitter.com/RUVo8Nlsdu — Chris Roberts (@Sidragon1) April 16, 2015

But a lawyer for Roberts said on Sunday that when his client received that call, the caller would only say he or she was from United, and wouldn’t give Roberts a name or callback number. When Roberts then tried calling the number back from his phone’s caller ID, it rang instead to a resort hotel, and Roberts assumed it was a prank call, Roberts’ lawyer said.

In recent weeks, Roberts gave media interviews in which he discussed airline system vulnerabilities.

“Quite simply put, we can theorise on how to turn the engines off at 35,000 feet and not have any of those damn flashing lights go off in the cockpit,” he told Fox News.

Roberts also told CNN he was able to connect to a box under his seat at least a dozen times to view data from the aircraft’s engines, fuel and flight-management systems.

“It is disappointing that United refused to allow him to board, and we hope that United learns that computer security researchers are a vital ally, not a threat,” said Nate Cardozo, a staff lawyer with the San Francisco-based Electronic Frontier Foundation, which represents Roberts.

Apparently just made front page Fox News..... pic.twitter.com/zS8uijWpYu — Chris Roberts (@Sidragon1) April 17, 2015

Cardozo said he hasn’t seen a copy of a search warrant that would have been used to seize Roberts’ electronics, and that he’s working to get the devices returned.

The FBI declined to comment on the matter.

The Government Accountability Office said last week that some commercial aircraft may be vulnerable to hacking over their on-board wireless networks.

“Modern aircraft are increasingly connected to the internet. This interconnectedness can potentially provide unauthorised remote access to aircraft avionics systems,” its report found.

Roberts took an alternate flight on Southwest Airlines and arrived in San Francisco Saturday evening. He speaks this week at the RSA Conference about computer security vulnerabilities.