The distance between the two planes closed to 2.94 miles before air traffic controllers at Andrews Air Force Base outside Washington directed the first lady's plane to abort a landing, the board said in a statement. The Federal Aviation Administration had previously said there was more than three miles between the planes, and had ordered controllers' supervisors to oversee flights carrying the first lady and the vice president. A supervisor was already required to monitors flights with President Barack Obama on board.
Obama's plane, a Boeing 737, was considerably smaller than the 200-ton C17 ahead of it. Federal regulations require five miles between planes to avoid dangerous wake turbulence when the plane in the lead is significantly larger than the one trailing.
The planes were lined up for their landing approach into Andrews by a controller at a regional radar facility in Warrenton, Va., the board said. The planes were already too close when controllers at Andrews took over.
The Andrews controllers immediately ordered the 737 pilot to execute a series of turns to increase its distance from the cargo plane. When the distance continued to narrow, the controllers directed the 737 pilot to abort the landing and circle the airport until the cargo jet cleared the runway.
On board the plane with Mrs. Obama was Jill Biden, wife of Vice President Joe Biden.
The board also said a Southwest Airlines jet with 142 people aboard came perilously close to a small plane over central Florida last month. The planes, traveling at hundreds of miles per hour, could have closed the short distance within seconds. They were flying at an altitude of about 11,000 feet at the time.
The board said previously that a controller at a regional radar facility near Jacksonville asked the Southwest pilot to fly close enough to look into the cockpit window of the smaller plane, a single-engine, four-seat Cirrus SR22. The Cirrus had been out of radio contact for over an hour.
Both planes landed safety. The controller has been suspended pending an investigation.
Also Friday, National Air Traffic Controllers Association President Paul Rinaldi called on the FAA to allow controllers to sleep on breaks during daytime shifts, and to take scheduled naps of as long as two hours during overnight shifts. Rinaldi also endorsed 10 other recommendations for combating fatigue offered by a working group of agency and union officials.
"If we are serious about addressing controller fatigue, then every recommendation must be adopted and implemented" Rinaldi said.
FAA Administrator Randy Babbitt and Transportation Secretary Ray LaHood have ruled out any change in policy to allow controllers to nap during work shifts, even on breaks. That's despite the disclosure since late March of at least five incidents of controllers dozing off at work.
Instead, Babbitt has increased by an hour the minimum amount of rest between work shifts. The FAA has also added a second controller on overnight shifts at 27 airports and a radar facility to prevent any more planes from landing without tower assistance because a controller working alone at night has fallen asleep.
Planes flew unguided because of a sleeping controller into Washington's Reagan National airport last month and in Reno, Nev., this month.
Rinaldi, while appreciative of the changes, said "they barely scratch the surface of the problem."
FAA officials declined comment.
The FAA has known for decades that controllers work exhausting schedules that can affect their ability to safely manage air traffic. The sleeping incidents, as well as recent errors by controllers, have shaken public confidence in the nation's air traffic system.
