Federal regulators ordered airlines to inspect the wings of more than 700 Boeing jets in response to a fire that destroyed a plane after it landed in Japan last week, officials said yesterday.
The inspections will affect more than 780 next-generation Boeing 737s operated by U.S. carriers, including AirTran and American, Southwest and Continental airlines.
The Federal Aviation Administration order focuses on the planes' slats, which are attached to the front edge of both wings and are deployed during takeoffs and landings to increase lift.
The order was prompted by an accident involving a China Airlines 737, which erupted in a fireball after landing on the Japanese island of Okinawa on Aug. 20, FAA officials said. All 165 people on board escaped uninjured.
The fire started after a loose bolt pierced the right wing's fuel tank, causing fuel to spill and ignite, investigators in Japan have said.
Investigators believe the bolt came loose because a worker did not re-install a washer on the slat's "downstop assembly" during a maintenance check that took place in the last few months, according to sources familiar with the probe.
Without the small washer, the assembly's bolt came loose and punctured the fuel tank, apparently when the slats were being retracted after the plane landed, the sources said.
China Airlines representatives could not be reached for comment.
The FAA's directive, issued Saturday, did not mention the China Airlines accident by name but explained its circumstances in detail. FAA officials confirmed the directive was referring to the incident.
The order also described a second incident in which a loose nut pierced a wing tank, causing fuel to leak. That did not lead to a fire, and the order did not name the carrier.
The directive requires airlines and other operators to inspect the slats within the next three weeks. Carriers are required to repeat the inspections every 3,000 landings.
Jim Proulx, a Boeing spokesman, said the company was working with carriers and regulators to help airlines comply with the inspection regimen. "This was determined to be an issue of flight safety," Proulx said. "It's very, very important."
Proulx said Boeing had received four reports in the past about loose nuts in slats. The airplane maker has issued several bulletins since December 2005 urging airlines to ensure the nuts on the downstop assemblies are properly installed and tightened. The most recent bulletin was sent last month, Proulx said.
Outside experts said the FAA and Boeing need to ensure that the inspections are done properly and that design flaws are quickly corrected because so many next-generation 737s are in service.
Bernard Loeb, a former top investigator at the National Transportation Safety Board, said the fire highlighted what investigators often learn after crashes: that parts that had seemed innocuous during the design and construction of an aircraft "can sometimes have catastrophic results."
"That is why we need to know more than just what happened, but why it happened," Loeb said.
The burnt-out wreckage of the aircraft. 
The United States Federal Aviation Administration has issued an emergency Airworthiness Directive to all owners and operators of certain Next Generation Boeing 737s to inspect their aircraft in light of recent developments in the investigation of the recent China Airlines explosion.

An example of a Boeing 737 in commercial operation
The measures have been imposed due to the discovery that a structural bolt in the aircraft that exploded had come loose and punched a hole in the aircraft's right wing fuel tank.

It is thought the bolt came loose after a worker failed to replace a washer after a routine maintenance procedure several months prior to the accident.

Boeing spokesman Jim Proulx said "This was determined to be an issue of flight safety... It's very, very important."

Operators must complete an initial inspection of the wing slat assemblies of the affected aircraft in ten days, and must ensure the fasteners are properly torqued within 24 days. They must then repeat the inspections every 3,000 flight cycles thereafter. The directive is believed to affect over 2,000 aircraft worldwide.