If you are planning on traveling in and out of Boston’s Logan International Airport, be very careful in the coming days.

According to News 6, the radar system is malfunctioning.

The Federal Aviation Administration said air traffic controllers were seeing phantom blips on their radar screens — planes that really weren’t planes at all.

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

At one point yesterday, some flights were being delayed by four hours or even more.

It’s not yet clear what is causing the problem, which was traced to a computer at the airport which feeds information to a regional F-A-A facility in New Hampshire.

Boston employers are recommending travel plans for their employees change to airports outside of the Boston area such as Manchester, NH and Providence Rhode Island.

Judy Rossi, who coordinates travel for Cambridge cancer-drug developer Vertex Pharmaceuticals Inc., said yesterday afternoon that most of the flights she wanted to book at other area airports were already filled. Rossi and her associates spent part of yesterday trying to locate Vertex employees who are scheduled to travel soon by plane. Some may rework their schedules or postpone meetings, she said.

”We can circumvent the situation,” said Rossi, Vertex’s associate director of corporate services.

Executives at EMC Corp., the Hopkinton data-storage company, said fewer business people were traveling because of the Columbus Day holiday. ”If this had happened on any other Monday, we would have gotten a lot of calls,” said Anne Pace, a company spokeswoman. Normally, about 340 EMC employees in North America travel daily, with half of them coming into or leaving Boston, Pace said.

Tourism officials took the news of the delays in stride. Several conventions are scheduled for Boston this week, including meetings of the American Trucking Association and the Congress of Neurological Surgeons. Officials said they do not expect Logan to have a major effect on the events.