The skin failure of a Southwest Airlines 737-300 en-route from Phoenix to Sacramento on Friday ended as well as it possibly could have, with the aircraft safely on the ground and no serious injury or loss of life, but it has brought the skin-cracking issue squarely into the public eye. While the manufacturers, carriers, regulatory agencies (and to some extent the perceptions of the traveling public) will determine the fate of the 737 classics, and Airbus’ similarly-aged short-haul aircraft, in the passenger fleet, we wonder what effects this incident may have on the freighter-conversion business.
If anybody in the conversion industry cares to add insights, I’d sure like to hear them. 737-300s and 737-400s are currently popular conversion candidates, and the first A320 was just inducted for conversion last week at EFW. If these aircraft types are suddenly retired in greater-than-anticipated numbers from passenger fleets, what will the effect be? And what about other types? Are other narrowbodies (757s for example) going to face the same problems? Widebodies?
Regarding the SWA incident, the first public comment from the NTSB was “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.” As far as we can determine, at the time of the accident the aircraft was at about 40,000 cycles and 49,00 hours — not particularly high. And in any case, cycles and hours only tell part of the story, as a high-cycle aircraft may have had fewer hard landings and suffered less turbulence than a younger unit.
It will be some time before full details of the cause of the failure are known, but Southwest responded by immediately grounding 79 of its 737-300s to check for skin-cracking. As I write this, nineteen have been declared safe and returned to service, while three have been found with cracking issues and held for further maintenance. The carrier said it expected to have the inspections completed by 5 April (tomorrow, as I write this). The photo above shows an SWA 737-300 at Paine Field for inspection.