A “gunshot-like sound” woke Brenda Reese as her Southwest Airlines flight cruised at 36,000 feet. Looking up, she could see the sky through a hole torn in the cabin roof.

The Boeing 737 lost cabin pressure after the hole developed Friday, prompting frightened passengers to grope for oxygen masks as the plane made a terrifying but controlled descent.

One passenger called it “pandemonium.” Another watched as a flight attendant and another passenger passed out, apparently for lack of oxygen, their heads striking seats in front of them.

Officials said Flight 812 lost pressure because of a fuselage rupture. Federal Aviation Administration spokesman Ian Gregor said the pilot made a “controlled descent from 36,000 feet to 11,000 feet altitude.”

His safe emergency landing at a military base in Yuma, about 150 miles southwest of Phoenix, drew applause from relieved passengers.

No serious injuries were reported among the 118 people aboard although a flight attendant was slightly hurt, according to Southwest officials. The cause of the hole was not immediately known. The FBI called it a “mechanical failure,” not an act of terror or other foul play.

The plane is a 15-year-old Boeing 737-300. Southwest officials said they would pull about 80 similar planes out of service for inspections of the fuselage, forcing the airline to plan to cancel roughly 300 flights Saturday.

Southwest operates about 170 of the 737-300s in its fleet of about 540 planes, but it replaced the aluminum skin on many of the 300s in recent years, spokeswoman Linda Rutherford said.  The roughly 80 planes being grounded have not had their skin replaced, she said.

“Obviously we’re dealing with a skin issue, and we believe that these 80 airplanes are covered by a set of (federal safety rules) that make them candidates to do this additional inspection that Boeing is devising for us,” Rutherford said.

Southwest officials said the Arizona plane had undergone all inspections required by the FAA, but they did not immediately provide the date of the last inspection.

The 737-300 is the oldest plane in Southwest’s fleet, and the company is retiring 300s as it take deliveries of new Boeing 737-700s and, beginning next year, 737-800s. But the process of replacing all the 300s could take years.

Reese said the plane had just left Phoenix Sky Harbor International Airport for Sacramento, Calif., when the “gunshot-like sound” woke her up. Oxygen masks dropped as the plane dove.

Seated one row from the rupture, Don Nelson said it took about four noisy minutes for the plane to dip to less than 10,000 feet. “You could tell there was an oxygen deficiency,” he said.

“People were dropping,” said Christine Ziegler, a 44-year-old project manager from Sacramento who watched as the crew member and a passenger nearby fainted. Nelson and Ziegler spoke after a substitute flight took them on to Sacramento.

Reese described the hole as “at the top of the plane, right up above where you store your luggage.”

“The panel’s not completely off,“ she told The Associated Press. ”It’s like ripped down, but you can see completely outside… When you look up through the panel, you can see the sky.”

Cellphone photographs provided by Reese showed a panel hanging open in a section above the plane’s middle aisle, with a hole of about six feet long.

The National Transportation Safety Board said an “in-flight fuselage rupture” led to the drop in cabin pressure aboard the plane.

A similar incident happened in July 2009 when a football-sized hole opened up in flight in the fuselage of another Southwest 737, depressurizing the cabin. The plane made an emergency landing in Charleston, W.Va. It was later determined that the hole was caused by metal fatigue.

Afterward, Southwest and the FAA reached an agreement specifying actions the airline would take to prevent another episode, said John Goglia, a former National Transportation Safety Board member and an expert on airline maintenance. The details of that agreement are considered proprietary and haven’t been made public, he said.

The latest incident “certainly makes me think there is something wrong with the maintenance system at Southwest and it makes me think there is something wrong with the (FAA) principal maintenance inspector down there that after that big event they weren’t watching this more closely,” Goglia said in an interview.

There was “never any danger that the plane would fall out of the sky,” Goglia said. “However, anybody on that airplane with any sort of respiratory problems certainly was at risk.”

Four months before that emergency landing, the Dallas-based airline had agreed to pay $7.5 million to settle charges that it operated planes that had missed required safety inspections for cracks in the fuselage. The airline, which flies Boeing 737s, inspected nearly 200 of its planes back then, found no cracks and put them back in the sky.

Julie O’Donnell, an aviation safety spokeswoman for Seattle-based Boeing Commercial Airplanes, confirmed “a hole in the fuselage and a depressurization event” in the latest incident but declined to speculate on what caused it.

Reese said passengers applauded the pilot after he emerged from the cockpit following the emergency landing at Yuma Marine Corps Air Station/International Airport.

“It was unreal. Everybody was like they were high school chums,” Ziegler said, describing a scene in which passengers comforted and hugged each other after the plane was on the ground.

“I fly a lot. This is the first time I ever had something like this happen,” said Reese, a 37-year-old single mother of three who is vice president for a clinical research organization. “I just want to get home and hold my kids.”

An FAA inspector from Phoenix and an NTSB crew were expected to be in Yuma on Saturday to investigate.

Holes in aircraft can be caused by metal fatigue or lightning. The National Weather Service said the weather was clear from the Phoenix area to the California border on Friday afternoon.

In 1988, cracks caused part of the roof of an Aloha Airlines Boeing 737 to peel open while the jet flew from Hilo to Honolulu. A flight attendant was sucked out of the plane and plunged to her death, and dozens of passengers were injured.

Three years ago, an exploding oxygen cylinder ripped a gaping hole the fuselage of a Qantas Boeing 747-438 carrying 365 people. The plane descended thousands of feet with the loss of cabin pressure and flew about 300 miles to Manila, where it made a successful emergency landing. No one was injured.