A provisional investigation in the United States has found that a Southwest Airlines jet suffered a structural failure when a hole opened in its fuselage.
The hole caused a sudden drop in cabin pressure and Flight 812 from Phoenix to Sacramento was forced to make a steep descent and emergency landing at a military base in Yuma, Arizona.
Southwest grounded 79 planes afterwards.
There were 118 passengers and crew aboard the plane. One flight attendant was slightly injured during the incident on Friday.
One passenger said she and her husband could see blue sky through the hole, as well as wiring and cabling.
She said many passengers were crying and terrified.
The National Transportation Safety Board said an "in-flight fuselage rupture" led to the sudden descent and drop in cabin pressure.
The BBC reports the same thing happened to another Southwest jet in 2009. Metal fatigue was the cause.
Cracks caused a hole to open in an Aloha Airlines plane over Hawaii in 1988. A flight attendant died during that incident.