Los Angeles ? A computerized system that guides arriving planes onto a runway at Los Angeles International Airport failed on Monday, delaying numerous flights around the country.

Two incoming flights were diverted, others were forced to circle the airport, and some planes were ordered to remain on the ground at other airports, officials said. Arriving flights were held up about 90 minutes. Departing flights were also delayed, and several flights were canceled.

Airport authorities worked around the problem about an hour and a half hour later.

Federal Aviation Administration spokesman Ian Gregor said the cause of the problem was unknown.

The malfunctioning piece of equipment, called a localizer, acts as a beacon to guide arriving planes onto runways. It is most crucial when it is foggy or hazy, and it was foggy at the airport Monday.

Because of a runway construction project, LAX, the world’s fifth-busiest airport, has three working runways – one handles arrivals, one handles takeoffs, and one handles both. It was the shared runway that had the problem.

The equipment used on that runway failed at 9:17 a.m., the FAA said. Airport authorities responded by reversing the direction of the runways so that the faulty equipment was no longer needed. Before that change was made, the number of landings, usually about one a minute, was reduced by half, said FAA spokesman Mike Fergus.

Technicians were able to repair the system by shortly after noon, allowing normal operations to resume.

Laney Fishera, 46, from Topsfield, Mass., said her flight from Boston circled above the ocean for about 30 minutes until a runway was available.

“We had to fly over the ocean, which was really weird,” she said.

It was the second serious problem in three weeks to disable part of the airport. LAX was hit with a major power failure July 18 that backed up flights across parts of the western United States and Canada.

That outage happened when a vehicle crashed into a utility pole, causing a power fluctuation that prompted the air traffic control center’s backup generator to turn on automatically. About an hour later, that generator failed.

Sen. Barbara Boxer, D-Calif., asked the FAA to investigate the failures.