On Saturday, United Airlines has stopped a security researcher from boarding a California bound flight after the researcher days earlier in a social media post has suggested that the airline’s onboard systems could be hacked.

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

The researcher, Chris Roberts is the founder of the One World Labs; they discover security risks before they are exploited.

On Wednesday, Roberts has been removed from the united flight by FBI after landing Syracuse, New York where he was questioned for four hours after jokingly suggesting on Twitter that he could get the oxygen masks on the plane to deploy.

They have seized Roberts laptop and other gadgets.

Roberts lawyer said the United didn’t give him detailed explanation why he wasn’t allowed on plane Saturday and he said that the airlines within 2 weeks will send him letter stating the reason.

Airline spokesman Rahsaan Johnson said, “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, however, we are confident our flight control systems could not be accessed through techniques he described.”

When asked what threat Roberts posed if United 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 that the airlines had reached several hours before to Roberts to tell him that he couldn’t fly.

The layer for Roberts said that the 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 tried to call back to the number, it rang instead to resort hotel, and Robert assumed it was a prank call.

In an interview Roberts said, “Quite simply put, we can theorize 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.”

Roberts took an alternative flight on Southwest Airlines and arrived in San Francisco Saturday evening.