On Friday, a hole opened in the cabin roof of a Southwest Airlines flight while it was en route from Phoenix to Sacramento with 118 passengers. Authorities say the service was only 18 minutes into its journey when the 1 foot wide, 5 foot long hole developed, causing the plane to lose cabin pressure. As the pilot conducted an emergency landing, the passengers put on their oxygen masks.

Robert Sumwalt, a member of the National Transportation Safety Board (NTSB), says the Boeing 737-300s data recorder shows that the plane was at 36,000 feet when the hole opened and then dropped to 11,000 feet in 4-and-a-half minutes. Ian Gregor, a Federal Aviation Administration (FAA) spokesman, says the pilot controlled the descent.

Sumwalt continued that the pilot initially planned to turn the plane around. However, he changed his mind after the flight attendants told him that they could see the sky through the hole. He made an emergency landing at a Yuma, Arizona military base, and only one of the stewardesses suffered minor injuries.

The NTSB member went on to say that inspectors found widespread cracking on the skin of the 737-300, as well as that it had separated at the lower rivet line where it comes together. They wouldn’t have seen this during a routine inspection, but it should have been noticed during major maintenance, the last of which was conducted in March last year. Mechanics were due to cut a 9 foot section out of the aircraft on Sunday, which will be sent to the NTSB’s lab in Washington for research.

Southwest airlines has been forced to ground about 79 of their Boeing 737-300 fleet for skin inspections, which has caused the cancellation of about 300 flights. As of Sunday night, there were reports that 2 other planes were found to have cracks.