BOSTON (AP) – A malfunctioning radar system triggered long delays at Logan International Airport on Monday, according to a Federal Aviation Administration spokeswoman.

Many flights were delayed by more than four hours after the radar surveillance system at an FAA facility in Merrimack, N.H., malfunctioned around 7:30 a.m.

Air traffic controllers were seeing “false targets” on their radar scopes – blips that the controllers knew did not represent planes in flight, said FAA spokeswoman Arlene Murray.

“A flock of geese can cause the problem, but this seems to be recurring,” Murray said. “It’s not a common problem. We have had it occur at facilities before.”

As a precaution, controllers increased the distance between planes from three miles to five miles.

“We basically slowed the system down a little bit until we can correct the problem,” Murray said.

It wasn’t immediately clear what caused the “false targets” to show up on the radar.

Logan was the only airport affected by the malfunction.

Georgeane Tacelli, spokeswoman for the Massachusetts Port Authority, said foul weather also contributed to the delays.