Low-flying military planes and helicopters spotted over midtown Manhattan last week turned out to be part of a training exercise on safely airlifting the next president out of New York City, law enforcement sources say.

The Federal Aviation Administration initially said that the U.S. military was conducting authorized flights over New York City last Tuesday with coordination of the federal body. The flyover of two Blackhawk helicopters and the military C-130 caused confusion: the city's Office of Emergency Management said it wasn't notified in advance by the FAA, and the NYPD was only given short notice.

Now law enforcement sources tell NBC 4 New York it was all part of a military training exercise -- an emergency relocation drill to figure out where a chopper could touch down near Trump Tower and move the president-elect and others out toward safety.

Retired Army Maj. Mike Lyons and a current military analyst says the mission may have also been looking at rooftops in the city that could help as possible evacuation routes.

"Police and law enforcement have got to be creative as terrorists could be in recognizing that during 9/11 they weren't able to evacuate anyone from the rooftop," he said. "The first thing they are likely looking at is a possibility from Trump Tower."