BA Boeing Co

By Andy Pasztor 

U.S. air-safety officials are investigating potential structural problems affecting hundreds of Boeing 737 jets following an in-flight incident that left a 12-inch rupture in the aluminum skin of a Southwest Airlines plane.

Nobody was hurt on Monday night's flight, en route from Las Vegas to Boise, Idaho, as the damaged aircraft descended to a safe altitude and the pilots landed at their destination, according to the carrier and the Federal Aviation Administration. The plane's cabin gradually lost pressure but it stabilized after pilots descended to a lower altitude, and oxygen masks never deployed.

The unusual event has prompted the agency to analyze whether more-frequent inspections should be ordered to check the integrity of the same part of the fuselage on similar 737 models.

The FAA analysis doesn't affect Boeing's 737 MAX models, which are newer and currently grounded around the globe.

Pilots on Southwest Flight 1685 descended to 22,000 feet from 39,000 feet and continued safely to their destination.

"The aircraft was able to maintain a safe cabin pressure," according to an FAA statement, adding that the agency is investigating.

A spokeswoman for Southwest said the plane was taken out of service and is being repaired. "We consistently review our maintenance programs based on new information and continually seek opportunities to improve our robust safety practices," she said.

Southwest has told the FAA that previously mandated maintenance checks found external cracks on two other 737s in the same location as with the plane involved in Monday's incident, according to people familiar with the details. But those cracks -- on top of the plane behind the cockpit -- didn't result in the kind of cabin decompression that occurred on the flight this week, according to information the carrier has provided to FAA inspectors.

Current FAA safety rules require inspections after every 1,500 flights to look for cracks on the exterior of that portion of the fuselage. The jet that landed safely in Boise was inspected roughly 500 flights before Monday's incident, according to a person familiar with the details.

Such maintenance checks for structural problems are routine safety initiatives across all airliner models.

The most serious result of cracks in an aircraft's body is a rapid decompression of the cabin. Such a problem can create a hole in the fuselage, through which, in extreme cases, passengers can even be sucked out in flight.

The FAA and Boeing have been devising enhanced maintenance procedures for the same section of what is called the crown of 737 jets since 2008. The original safety directive was replaced by revised inspection requirements in 2016 and again in 2017.

It is too early to know whether the FAA will require more-frequent inspections, according to another person familiar with the details. Before any decision, FAA experts are expected to review the service and maintenance history -- as well as the structural integrity of certain modifications -- affecting Southwest and other U.S. operators of the widely used 737 models.

In 2016, the FAA's maintenance order called on airlines to look for missing or loose fasteners and laid out other measures intended to prevent cracks from spreading.

The 2017 safety directive said Boeing determined that the skin of certain 737 models is subject to widespread metal-fatigue damage. If the weakness isn't detected and corrected, according to the FAA, it could "result in reduced structural integrity of the airplane."

The FAA's deliberations come five months after the agency ordered emergency structural inspections of some older 737 NG jets, in order to detect unrelated cracking in crucial components that help connect wings to fuselages. Subsequently, there were checks and repairs, as necessary, of 737 NG jets that had flown fewer trips. Dozens of planes world-wide have been grounded and repaired, causing some schedule disruptions.

Southwest, for its part, has had regulatory tussles over the years with the FAA regarding structural inspections and other maintenance issues. More than a decade ago, after Congressional investigators revealed Southwest flew tens of thousands of passengers on 46 older aircraft without completing mandatory structural inspections, the carrier agreed to pay a $7.5 million civil penalty. Years later, metal fatigue opened a 5-foot gash on a Southwest 737 that ended up making an emergency landing at a military base in Arizona. There were no injuries.

Write to Andy Pasztor at andy.pasztor@wsj.com

(END) Dow Jones Newswires

March 13, 2020 23:57 ET (03:57 GMT)

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