PHOENIX — A terrifying flight emergency caused by a fuselage hole 34,000 feet over the Arizona desert is focusing attention on the hundreds of older-model 737s around the world that could be similarly vulnerable.
A 5-foot section of the passenger cabin roof of a 15-year-old Boeing 737-300 tore off April 1, forcing the Southwest Airlines flight to make an emergency landing.
None of the 118 people aboard was seriously injured, but light-headed passengers were banged around the cabin and had to quickly put on overhead oxygen masks as pilots made a rapid descent.
The planes will now be subjected to repeated examinations as the problem revealed by tiny, hard-to-find stress fractures in the aluminum skin resonates through the world's 737 fleet for years to come.
The Boeing 737 is workhorse of international aviation. Airlines and governments are giving the planes a closer look and taking swift action.
Japan, Indonesia, South Korea and others ordered airlines to beef up inspections. Scandinavian airline SAS is performing similar checks on some of its 737s. Qantas Airlines in Australia is checking four of its planes and Air New Zealand is looking at 15. Airlines said the inspections have not disrupted air travel.
Southwest and Continental Airlines have the most planes on the list of 737-300s, 737-400s and 737-500s prone to the fuselage ruptures, but a large number of the planes are owned by overseas carriers. UTAir in Russia, Garuda Airlines in Indonesia, Air New Zealand and three major carriers in China are among the biggest. Alaska Airlines has 17.
Southwest finished inspecting all of its affected planes by Tuesday. They found five that had cracks in the same lap joint that tore open during last week's flight, and were working with Boeing to make repairs. Alaska Airlines is going a step beyond a Federal Aviation Administration directive this week that ordered inspections when the planes reach a 30,000 takeoffs and landings; the airline will inspect all its planes in the coming weeks.
"We're not required to inspect them right now, but we felt it was the prudent thing to do, and to help the industry determine the proper interval," spokesman Paul McElroy said.
There are about 6,000 737s in operation worldwide, and an emergency FAA order on Tuesday only covers 579 that have the type of "lap joint" that failed during last week's flight. Lap joints are used in many places on an aircraft fuselage and get their name because it is the spot where the aluminum skin of the aircraft overlaps and is secured with rivets. The FAA order focuses on a Boeing joint design on planes made between 1993 and 2000.
Experts say that all of the planes around the world will be covered by the FAA order because of international agreements between civil aviation regulators globally. Many of the inspection orders handed down by foreign governments mirrored the one issued by the FAA.
Henry Harteveldt, aviation analysis at Forrester Research, Inc. in San Francisco, said that some airlines may not always maintain their airplanes to the highest levels of safety. "But I would make very clear that the top tier U.S. and foreign flag airlines do this. Airlines like British Airways, Qantas and so on, those airlines maintain their airplanes to the highest standards and the best record-keeping."
The FAA said all of the planes have to undergo inspections when they reach the threshold of 30,000 takeoffs and landings. The 175 of those planes that have already reached the threshold are getting immediate inspections.
For example, the planes owned by the crown prince of Thailand and Chinese Air Force have only flown about 5,000 cycles each, meaning their planes have a long ways to go before an inspection. One of the Swedish planes has more than 40,000, requiring an immediate examination.
The inspections are high-tech and labor-intensive.
Mechanics using a device that sends magnetic signals through metal to detect unseen cracks will scan about 50 feet of the twin metal seams running along the top of each airplane. The task takes two experts in aircraft service about eight hours. Repairs on any fatigue cracks will take a day or two at most. The checks will have to be repeated every 500 flights.
Boeing redesigned the lap joint on 737s in the early 1990s and thought airlines wouldn't need to inspect them closely until 60,000 flights. That was a mistake, a top Boeing engineer acknowledged this week, and the company was surprised by the failure of the 15-year-old Southwest jet that had flown fewer than 40,000 flights.
Indeed, Continental and Alaska Airlines are inspecting airplanes that are years from the new FAA threshold as an extra precaution, the companies told The Associated Press.
Continental, now merged with United Airlines, has 32 of the 737s in question, none with more than 30,000 cycles that would make them subject to the immediate inspection order. Nonetheless, the twin joints that hold the skin together along the top of the airplane will be inspected as they come due for major maintenance in the coming 18 to 24 months.
The first Boeing 737 entered commercial service in 1968, and 6,725 have been delivered since then. Very few of the early models, with their distinctive cigar-shaped engines, are still flying.
A 737-200 model flying for Aloha Airlines in 1988 had one of the most spectacular aviation incidents in modern history when its roof ripped off while flying from Hilo to Honolulu. A flight attendant was sucked out of the plane and plunged to her death, and dozens of passengers were injured.
That tragedy was blamed on the failure of the same type of metal joint that forced Southwest Airlines Flight 812 to make an emergency landing near Yuma, Ariz.
The Aloha incident triggered a decades-long effort to prevent similar stress-related failures that came to a conclusion in January when new FAA regulations went into effect mandating closer inspections.
On Thursday, FAA Administrator Randy Babbitt ordered a review of the new safety regulation, saying the agency needed to find out why the cracks in the latest incident were not detected.
Independent aviation consultants were also worried by the failure.
"The one thing we have to be worried about this is that we were surprised by that crack," said Hans J. Weber, president of San Diego-based aviation consulting firm TECOP International, who worked extensively on the aging aircraft program. "After all that work, that we again have an aging aircraft surprise, that bothers me."
It remains important to remember, Harteveldt said, that all airplanes have problems, and have ever since modern jet transportation changed travel in the mid-1950s.
"To Southwest's credit, when that skin ruptured on that plane a week ago or so, that pilot got that plane down from 34,000 to 10,000 feet or so in (four) minutes. No one was severely hurt, no one died, and I think that is an important point to keep in mind," Harteveldt said. "I think people will view this as a hiccup, I don't believe that it will have a long-term effect on the 737."
Associated Press Writer Scott Mayerowitz contributed to this report from New York.