United Airlines temporarily grounded 11 percent of its fleet and cancelled 31 flights Wednesday while it tested dozens of Boeing 777s to make sure components of a cargo fire suppression system were operating effectively.

The inspections are the latest to affect the U.S. airline industry and its passengers, roiled by a series of similar moves in recent weeks as carriers review their maintenance records in an atmosphere of increased regulatory scrutiny.

The Chicago-based airline said testing would be done on 52 777s over a period of 36 hours. Spokeswoman Jean Medina said 14 planes had been inspected and cleared to fly by late morning.

The carrier has about 460 aircraft.

Delays were reported in Japan and Hawaii Wednesday morning and the airline warned passengers to be prepared for other delays and cancellations as it proceeded with the inspections. Medina said 31 of 84 scheduled 777 flights had been cancelled.

United, a subsidiary of UAL Corp., said a review of maintenance records showed a test on one of five bottles in the fire suppression system hadn't been performed. The airline alerted authorities.

The planes, which have a so-called "intuitive" self-diagnostic system that would have detected any malfunction with the fire suppression system, mostly fly international routes and from the carrier's major hubs.

United carried out unscheduled maintenance on seven of its Boeing 747 jets last month but found no safety-related issues.

The Federal Aviation Administration has been checking maintenance records at all domestic airlines after revelations surfaced about missed safety inspections at Southwest Airlines Co.

UAL shares fell 54 cents, or 2.3 percent, to $22.59 in midday trading Wednesday.

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