Southwest Airlines says it has returned 19 of its 737s to service after a hole on the top of one of the carrier's 737-300s triggered a decompression incident, forcing the the aircraft to make an emergency landing in Yuma, Arizona on 1 April.
After the incident Southwest said it on 2 April was examining 79 aircraft "in accordance with airworthiness directives for skin fatigue over the course of the next several days at five locations". Flightglobal's ACAS database shows Southwest operates 170 -300s , 25 -500s and 355 -700s.
As of 16:00EST on 3 April, 19 aircraft had undergone intense inspections and returned to service, says Southwest. Testing of two aircraft revealed small subsurface cracks on each fuselage. Those inspections entailed non-destructive test in high frequency eddy current conditons on the aircraft skin, which detects any subsurface fatigue not visible to the human eye.
"Further evaluation and potential repairs will be necessary before those planes are returned to service," Southwest states.
Southwest anticipates completing inspections by late on 5 April.
US National Transportation Safety Board member Robert Sumwalt on the scene in Yuma on 3 April stated: "We have clear evidence the skin separated at the lower rivet line. A preliminary onsite examination reveals pre-existing fatigue along the entire fracture surface."
Sumwalt says the decompression occurred 18.5m after takeoff, and there were no overt or abnormal indications prior to the event.