US low-cost carrier Southwest Airlines is to ground over 80 Boeing 737 aircraft pending immediate inspections after a fuselage hole was discovered in a jet that depressurised on a service to California.

Southwest says that it has "decided to keep a subset of its Boeing 737 fleet out of the flying schedule" to commence an "aggressive inspection effort".

It says 81 aircraft are affected by the checks and that these will be examined over the next few days. The jets are covered by US FAA airworthiness directives detailing checks for skin fatigue.

Southwest has taken the action after one of its 737-300s, operating flight WN812 between Phoenix and Sacramento, diverted to Yuma yesterday after a loss of cabin pressure and deployment of oxygen masks.

"Upon landing safely in Yuma the flight crew discovered a hole in the top of the aircraft," says the carrier, adding that it was located about mid-cabin. It has not indicated the size of the rupture.

One of the 118 passengers and one of the five cabin crew members were treated for minor injuries.

The aircraft involved, identified by the US National Transportation Safety Board as bearing registration N632SW, carries serial number 27707 and is a 15-year old airframe.

"We have launched personnel to Yuma to begin the investigation process with the NTSB, FAA and appropriate parties to determine the cause of the depressurisation," says Southwest chief operating officer Mike Van de Ven.

It says it is working with Boeing on the details of the inspections for the aircraft.

Southwest suffered a similar incident two years ago when a Nashville-Baltimore service - also operated by a 737-300 - diverted to Yeager after being holed in its upper fuselage in July 2009.

Investigation attributed the hole to fatigue cracks and the incident prompted the FAA to mandate a Boeing service bulletin covering fatigue checks on certain older-variant 737s.

Source: Air Transport Intelligence news