DALLAS — Federal investigators say metal fatigue caused a hole to rip open in the roof of a Southwest Airlines jet as it cruised at 35,000 feet last year.
The National Transportation Safety Board says the 14-inch crack developed in a spot where two sheets of aluminum skin were bonded together on the Boeing 737 jet.
Southwest spokesman Brad Hawkins said Thursday that the airline agreed with the board’s findings and had increased visual inspections of that area of the skin on its planes.
bound from Nashville, Tenn., to Baltimore on July 13, 2009, lost cabin pressure, causing oxygen masks to drop in front of passengers. The pilot made an emergency landing in Charleston, W.Va. There were no injuries among the 126 passengers and five crew members.
Two months after the scare, Boeing told all airlines with 737s to conduct repeated inspections of the top of the fuselage near the vertical tail fin. The Federal Aviation Administration has since made those inspections mandatory.
Southwest got the plane in 1994 — it’s much older than the average Southwest jet — and had flown it for 50,500 hours and made 42,500 takeoffs and landings before it sprang a hole in the roof, according to the safety board report.
The safety board said it found signs of metal fatigue by magnifying the area in front of the tail fin. In a 3-inch stretch, the crack penetrated completely through the aluminum skin.
FAA records showed that eight cracks had been found and repaired in the fuselage during the plane’s 14-year checkup six months before the Charleston landing.
Hawkins, the Southwest spokesman, said the airline was complying with all new safety regulations developed by Boeing and the FAA since the Charleston incident.
“We’ve taken aggressive measures to incorporate additional maintenance inspections … in response to what was learned from Flight 2294,” he said.
The FAA requires special inspections for wear and tear, which is common among planes of that age. A few months before the emergency landing, Southwest had agreed to pay $7.5 million to settle charges that it operated planes without performing those inspections, although at the time the FAA’s requirement didn’t cover checking the area directly in front of the vertical tail fin.
Metal fatigue has caused catastrophic accidents. In 1988, cracks caused part of the roof of an Aloha Airlines Boeing 737 to rip open in flight and a flight attendant plunged to her death. That accident led to tougher inspection rules.
Dallas-based Southwest has a fleet of 541 planes, all of them Boeing 737s. The airline says the average age of its planes is 10.5 years.