Michelle Obama's plane ‘too close’ to cargo jet

They decided her Boeing 737 passenger jet was too close to a huge C-17 cargo jet in front.

However, they said there was little risk to Mrs Obama and to the Vice-President's wife who was also on board.

The episode puts the Federal Aviation Administration back into the spotlight as officials struggle to calm jitters about flying that have been raised by the suspension of nine air traffic controllers and supervisors around the country in recent weeks, including five for sleeping on the job.

The first disclosed case of a controller falling asleep on duty occurred 23 March at Washington's Reagan National airport, not far from Andrews.

The latest incident happened at about 5pm on Monday when the Boeing belonging to the Air National Guard - one of several guard planes used by the White House - came within about five kilometres of the C-17 as the planes were approaching Andrews to land, according to officials.

The FAA requires a minimum separation of eight kilometres between two planes when the plane in the lead is as large as the 200-ton cargo jet, in order to avoid dangerous wake turbulence that can severely affect the trailing aircraft.

There were also concerns that there might not be enough time for the cargo plane to clear the Andrews runway before Mrs Obama's plane landed.

The pilot was directed to execute a “go-around” to stop descending and start climbing and circle the airport.

Aviation safety expert John Cox said an accident was unlikely.

"Every professional pilot I have ever known has been in a situation where they were overtaking the plane in front of them and asked to do an S-turn," he said. "The only issue that could have come up was if they'd encountered the wake of the C-17."