United Airlines grounded 52 aircraft for overdue safety inspections on components of their fire suppression systems in the cargo hold. The grounded planes amount to approximately 11 percent of the airline's fleet.

As part of a regular review of maintenance records, United said it discovered that a functional test on its Boeing 777 planes had not been performed. The company notified the FAA and began performing the checks. As many as 12 planes were inspected by midmorning on Wednesday. The rest of the inspections are expected to be completed within 36 hours. Some delays were reported in Japan and Hawaii. The company advised passengers to check its Web site for information about flights.

The Federal Aviation Administration on March 6 fined Southwest Airlines $10.2 million for operating 46 planes that had not been properly inspected. FAA subsequently grounded airplanes at Delta and American Airlines.