US President Donald Trump's Qatari-gifted Air Force One was delayed on the tarmac on Wednesday after an emergency inflatable slide accidentally deployed, raising fresh questions over the safety of the jet.

Trump, who was preparing to travel to a Republican Party convention in Dallas from Joint Base Andrews, had to wait in his helicopter before being able to board the plane following the incident.

The 80-year-old then told reporters that inspectors were checking one of the Boeing 747's inflatable slides used for emergency evacuations.

"They're checking the slide over here, and I think it's going to take 15 minutes," Trump said on the tarmac before boarding.

But a person briefed on the situation later told AFP that "military personnel accidentally triggered the slide".

The plane's safety has been the subject of doubt, and the issue came to a head during a recent dramatic incident in Turkey, where Trump secretly switched to a different aircraft amid security concerns.

Asked if Trump was sure the jet was safe, he responded: "Yeah I am, or I wouldn't be on it."

Upon arrival at Joint Base Andrews near Washington, Trump remained on his helicopter for an unusually long time before finally boarding Air Force One.

An inflatable slide was seen deployed on the right side of the jet.

The plane eventually took off and landed in Texas, where Trump is to speak at a Republican convention in a bid to rally his party ahead of November's midterm elections.

The Qatari plane, repainted in a red, white and blue livery chosen by Trump, was last in the spotlight in July, when Trump decided at the last minute not to join press and top administration members on the jet leaving the NATO summit in Turkey.

Trump pretended to board the old Air Force One as planned -- only to secretly deplane from a different door, into a catering truck that took him to a third plane.

The move was in response to a reported security threat from Iran involving a surface-to-air missile. (AFP)



Edited by Altis Wong