PHOENIX — The airliner whose roof ripped open 34,000 feet over Arizona has had a busy 15-year life: taking off and touching down more than seven times a day, on average, and possibly developing microscopic cracks in its aluminum skin each time.
Federal aviation officials were preparing to issue an order Tuesday that calls for emergency inspections on 80 U.S.-registered Boeing 737 jetliners with histories similar to that Southwest Airlines jet, which had been pressurized and depressurized 39,000 times before a 5-foot-long hole opened in its fuselage.
The order is aimed at finding weaknesses in the metal exterior, but virtually all of the affected aircraft will have already been inspected by the time the order takes effect.
The safety directive applies to about 175 aircraft worldwide, including 80 planes registered in the U.S., the Federal Aviation Administration said. Of those 80, nearly all are operated by Southwest. Two belong to Alaska Airlines.
Southwest grounded nearly 80 Boeing 737-300s for inspections after its jet leaving Phoenix lost pressure Friday, forcing pilots to make an emergency landing 125 miles away in Yuma. By Monday evening, 64 were cleared to return to the skies, but three were found with cracks similar to those found on the Arizona plane.
Friday's incident, however, raised questions about the impact that frequent takeoffs and landings by short-haul carriers like Southwest put on their aircraft and the adequacy of the inspections.
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.
But airlines, manufacturers and federal regulators have known since at least 1988 that planes can suffer microscopic fractures. That year, an 18-foot section of the upper cabin of an Aloha Airlines 737-200 peeled away in flight, sucking out a flight attendant.