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

A “gunshot—like sound” woke Brenda Reese as her Southwest Airlines flight cruised at high altitude, heading for California. Looking up, she could see the sky through a hole in the roof.

The Boeing 737 lost cabin pressure after the hole developed on 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 two people passed out, apparently for lack of oxygen.

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 to 11,000 feet (11,000 to 3,350 meters) altitude.

His safe emergency landing at a military base in Yuma, about 150 miles (240 kilometers) southwest of Phoenix, drew applause from relieved passengers.

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

Reese said the plane had just left Phoenix Sky Harbour International Airport for Sacramento, Calif., when the “gunshot—like sound” woke her up. She said 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 get lower in the sky. “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 a crew member and a passenger fainted.

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

Cellphone photographs provided by Mr. Reese showed a panel hanging open above the plane’s middle aisle, with a hole about six feet (two meters) long.

The National Transportation Safety Board said an “in—flight fuselage rupture” led to the drop in cabin pressure aboard the 15—year—old plane.

“It was unreal. Everybody was like they were high school chums,” Mr. Ziegler said, saying passengers hugged each other after the plane landed.

“I fly a lot. This is the first time I ever had something like this happen,” said Ms. Reese, a 37—year—old single mother of three. “I just want to get home and hold my kids.”

Mr. Gregor said an FAA inspector from Phoenix was en route to Yuma. The NTSB said it also was sending a crew to Yuma.

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

In October 2010, a cabin lost air pressure when a hole ripped open in the fuselage of a Boston—bound American Airlines flight from Miami, also forcing an emergency landing.

In 1988, a Boeing 737 blew open at 24,000 feet (7,300 meters) when a 20—foot (6—meter) section of the aircraft’s upper fuselage ripped off. An Aloha Airlines flight attendant was sucked out of the jet and killed, and 61 passengers were injured.

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

Meanwhile, two flight attendants reported dizziness and four passengers fainted aboard an American Airlines flight on Friday from Washington to Chicago, forcing the pilot to drop the jet’s oxygen masks and land in Dayton, Ohio.

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