Cracks have been discovered in three Southwest Airlines 737 aircraft subject to inspection following the forced landing of Southwest flight 812 on 1 April.
The crew of the Phoenix-Sacramento flight landed in Yuma, Arizona, following depressurisation caused by a rupture in the roof of the mid-cabin section of the fuselage.
The airline said on 2 April that it had begun work with the US National Transportation Safety Board (NTSB) and the Federal Aviation Administration (FAA) to determine the cause of the incident.
Similarly, Southwest Airlines and Boeing have developed an inspection regimen to assess the damage to the aircraft and develop an inspection regimen to scrutinise 79 of its 737-300 aircraft, which are covered by FAA Airworthiness Directives aimed at inspections for aircraft skin fatigue.
The inspections involve a non-destructive test (NDT) in the form of high-frequency eddy current of the aircraft skin. This test is designed to detect any subsurface fatigue in the skin that is not visible to the eye.
The NTSB says it has been told that cracks have been identified in lap joints of three aircraft under inspection by Southwest.
The aircraft involved in the incident on 1 April also had additional cracks in portions of the lap joint along the fuselage.
So far, 57 aircraft have been checked and returned to service, with the remainder of the checks likely to be completed by late 5 April.