WASHINGTON — The Federal Aviation Administration plans to order immediate inspections of older-model Boeing 737 jetliners that are the workhorse of domestic air travel, a precaution after a hole opened in the hull of a Southwest Airlines plane flying at 34,400 feet on Friday.
There are more than 1,200 Boeing 737s in use by American air carriers, providing much of the nation's intercity air travel. The inspection order will apply to about 80 planes that were delivered before 1990, the FAA said.
Most of those planes — in the -300, - 400 and -500 series — are operated by Southwest, the FAA said. Two belong to Alaska Airlines.
"Safety is our No. 1 priority," Transportation Secretary Ray LaHood said in a statement. "Last Friday's incident was very serious and could result in additional action depending on the outcome of the investigation."
The statement came shortly after Boeing said it was preparing a service bulletin that would recommend "lap-joint" inspections on certain 737 planes.
Friday's incident unfolded at nearly 35,000 feet with the sound of an explosion during the flight of a 15-year-old Boeing 737-300 carrying 118 passengers from Phoenix to Sacramento, Calif. Some passengers reported feeling dizzy during the swift loss of cabin pressure. Oxygen masks were released and at least two people passed out as the pilot guided the plane to an emergency landing at Yuma Marine Corps Air Station in Arizona. No one was seriously injured.
Southwest grounded 79 Boeing 737s for inspections after the incident — subsurface cracks were discovered in three other 737-300s. By late Monday, the airline said 64 of its 79 planes had been inspected and returned to service. Inspections of the rest were scheduled to be completed by today.
The airline canceled 70 of its scheduled 3,400 departures Monday. About 300 flights were canceled on both Saturday and Sunday. Southwest is the top carrier at Tampa International Airport.
The FAA ordered inspections of planes from the -300, -400 and -500 series that have accumulated more than 30,000 flight cycles — one takeoff and one landing. The aircraft involved in Friday's incident had 39,000 cycles, and nearly 46,000 hours of flight.
Initial inspections will use electromagnetic, or eddy-current, technology in areas of the fuselage, the FAA said. Regular followup inspections will be required.
Late Sunday, another Southwest flight carrying 142 people was diverted to Los Angeles International Airport because of a burning electrical smell in the passenger cabin, but the airline said it was unrelated to the issue affecting the flight on Friday.
The 737-300 model had been flying from Oakland, Calif., to San Diego, said Christi McNeill, a Southwest spokeswoman. No one was injured, and the passengers swapped aircraft and went on to their destination, she said.
The problem "was a gasper fan," said McNeill, referring to the system related to the vents above the seats. "If it gets overheated it can release a foul odor into the cabin."
The National Transportation Safety Board said Sunday that the hole on the Friday flight was caused by fatigue cracks in the aluminum underskin of the lap joints in the plane. According to FAA records, the airline identified and fixed 21 cracks in the fuselage of the plane 11 months ago during a scheduled inspection. Outside airline maintenance specialists say such fatigue cracks are not uncommon in older jets.
Cracks can develop from the constant cycle of pressurizing the cabin for flight, then releasing the pressure upon landing.
Since there had been no previous accidents or major incidents involving metal fatigue in the middle part of the fuselage, Boeing maintenance procedures called only for airlines to perform a visual inspection.
All of Southwest's 548 planes are 737 models, and they accumulate flight cycles more rapidly than some other carriers as they shuttle among several cities each day.
By contrast, the other two U.S. carriers with sizable 737 fleets — American Airlines and United-Continental Airlines — generally use those planes on longer flights and accumulate flight cycles more slowly.
Southwest has a history of maintenance problems. In 2008, the FAA proposed a $10.2 million penalty, later reduced to $7.5 million, for Southwest's failure to do mandatory inspections for fuselage fatigue cracking on some of its Boeing 737s.
Information from the Washington Post, New York Times and Associated Press was used in this report.