DALLAS — Federal safety officials are investigating how a foot-long hole opened in the top of a Southwest Airlines jet, forcing the aircraft to make an emergency landing in Charleston, W.Va.
The Boeing 737 jet lost pressure in the cabin, but no one was injured on Monday's Nashville-to-Baltimore flight that carried 126 passengers and five crew members.
The plane was built in 1994, and government records indicated that an inspection in January turned up eight cracks in the frame that required repairs.
Southwest said Tuesday that it inspected all 181 of its identical Boeing 737-300 series jets overnight before putting them back in the sky.
Southwest is the biggest airline at Tampa International Airport, carrying 30 percent of all travelers through the first five months of 2009. Only a handful of Southwest flights were 30 minutes or more late in departing and arriving Tuesday at TIA, according to the Web site flightstats.com.
Southwest said it was unclear what caused the hole, which ripped open just in front of the vertical tail fin as the plane cruised at 30,000 feet. The jet flew on for nearly half an hour to Charleston.
Federal Aviation Administration records show that during the plane's 14-year checkup in January, eight cracks were found in the fuselage frame and repaired.
Damage from wear and tear is not unusual in planes that old, and the FAA requires special inspections for cracks. In March, Southwest agreed to pay $7.5 million to settle charges that it operated planes that had missed those required inspections.
FAA spokesman Lynn Lunsford said an initial review indicated that inspection orders for the Boeing 737-300 didn't include inspecting the area of the body where the tear appeared on Monday's flight.
Experts said the tear could have been caused by damage from a dent or ding, or the plane's skin could have suffered from age-related fatigue. Jet cabins are pressurized and depressurized with every flight, which can cause tiny cracks over time.
Bill Voss, president of the Flight Safety Foundation in Alexandria, Va., said a finding of fatigue would be more frightening. If that were the cause, it could force the FAA to consider more rigorous inspections for older aircraft, he said.
Alten "Skip" Grandt, an aeronautics professor at Purdue University who specializes in structural analysis, said that the fuselage of the Boeing jet performed as designed by preventing a sudden and catastrophic loss of pressure, and stopping the hole from expanding.
Michael Cunningham, a passenger on the Nashville-to-Baltimore flight, told NBC's Today show Tuesday that he had dozed off in his seat in mid cabin when he was awakened by "the loudest roar I'd ever heard," and saw the hole above his seat.
Cunningham said people stayed calm and put on oxygen masks that dropped from the ceiling.
"After we landed in Charleston, the pilot came out and looked up through the hole, and everybody applauded, shook his hand, a couple of people gave him hugs," he said.