FBI says no foul play suspected in Southwest accident

Inspectors from the Federal Aviation Administration and the National Transport Safety Board are en route to Yuma, Arizona to investigate why a Boeing 737 developed a hole in its cabin that forced it to make an emergency landing.

Passengers aboard Friday's Southwest Airlines flight reported hearing a sound like a gunshot, followed by pandemonium as oxygen masks dropped from the ceiling and the plane made a terrifying but controlled descent, dropping 7,600 metres in roughly four minutes before touching down at a military base about 240 kilometres southwest of Phoenix

So far the NTSB has only said that Flight 812 lost pressure because of an "in-flight fuselage rupture," the cause of which remains a mystery.

The FBI has already ruled out terrorism or other foul play, describing the incident as a "mechanical failure."

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

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.

A similar incident on a Southwest plane to Baltimore in July 2009 also forced an emergency landing when a 30 centimetre-long hole opened in the cabin.

No serious injuries were reported among the 118 people aboard Friday's flight, although a flight attendant was slightly hurt, according to Southwest officials.