Washington (CNN) -- A plane carrying Michelle Obama had to abort its landing on Monday after it came too close to a military C-17 cargo plane ahead of it, according to a senior administration official and the Federal Aviation Administration.

The planes -- which were both trying to land -- were three miles apart, when they are supposed to be five miles apart, the official told CNN. The Federal Aviation Administration is investigating what went wrong, as it is believed to be an air traffic controller mistake, the official said.

The White House does not believe the first lady's life was ever in danger, the senior official said.

The FAA said in a statement controllers at Andrews Air Force Base instructed an incoming Boeing 737 to perform a "go around" "because the plane did not have the required amount of separation" behind the military plane.

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The FAA is investigating. "The aircraft were never in any danger," the agency said.

The landing was briefly aborted and Obama's plane had to circle, the official said.

Obama was actually on a C-40, a military version of the 737 that was part of the Air National Guard -- not the regular Air Force fleet used by VIPs at Andrews, said Maj. Michelle Lai of the 89th Airlift Wing at Andrews Air Force Base.

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The FAA did not want Obama's plane to be caught in the "jet wash," of the C-17 as it landed, Lai said. That refers to the force of the air from the back of the C-17.

"It's important to know the FAA made the right call and at no time was the first lady's life in danger," Lai said.

When the Potomac TRACON, the regional radar facility, handed off the plane to the Andrews Air Force Base tower, the planes were three miles apart, a government official told CNN. "Both facilities knew how far apart they were" at the time of the handoff, the official said. But the official declined to say why the hand-off occurred.

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The TRACON could have slowed Obama's plane down or order it to turn earlier, the official said. Why that wasn't done is under investigation. But "it was a controlled situation," the government official said.

The National Transportation Safety Board said it was gathering information on the incident and will be making an assessment to determine whether it will investigate more closely.

CNN's Ed Henry, Jeanne Meserve and Mike Ahlers contributed to this report.