Southwest Airlines has started repairs on the lap joints of five Boeing 737s after finding minor subsurface cracking on the aircraft.

The repairs stem from a decompression event on a 737-300 Classic on 1 April, which forced the aircraft to make an emergency landing in Yuma, Arizona.

In the aftermath, the FAA issued an airworthiness directive requiring inspections of certain Classic 737s at every 500 cycles.

Boeing has provided repair instructions to Southwest for the five aircraft, which includes the removal and replacement of an 18in section of the lap joint, with a completion time of 8-16 hours.

Pending FAA approvals, Southwest anticipates returning four of the five aircraft to service on 9 April, with one aircraft remaining in previously scheduled maintenance.

Southwest has no repair update for the aircraft involved in the incident at this time, but N632SW has been released from the onsite investigation by the US National Transportation Safety Board (NTSB).

Southwest states that Boeing asked operators of 737 Classics with line numbers 2553 and 3132 inclusive, which were delivered between 1993 and the end of the Classic's production run in 2000, with above 30,000 cycles to inspect certain lap joints.

"Although Southwest does operate a small number of 737-500 aircraft, the FAA's Airworthiness Directive focuses on a particular set of 737-500 airplanes which are not included in the Southwest fleet," the carrier states.

Continental has previously told ATI its 32 737-500s are newer models with less than 25,000 cycles.

Source: Air Transport Intelligence news