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

A few 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 45 minutes on average, and departing flights were also delayed.

Airport authorities worked around the problem about an hour and a half hour later, and operations were expected to be back to normal by mid-afternoon.

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 the fix was made, the number of landings, usually about one a minute, was reduced was by half, said FAA spokesman Mike Fergus.

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 automatically turn on. About an hour later, that generator failed.

The airport averages 1,800 daily flights and will serve an estimated 18.7 million passengers this summer, 200,000 more than last year.