Small, subsurface cracks found in Southwest Airlines planes

Southwest Airlines Co. (LUV) said it will scrub 100 more flights today and reported "small, subsurface cracks" in two jets during inspections for metal fatigue after a plane's fuselage tore open in flight.

The dropped flights follow 300 cancellations yesterday, or 9 percent of the schedule, said Chris Mainz, a spokesman. Checks on 21 Boeing Co. (BA) 737-300 planes found two that needed repair, and 19 others were returned to service, Southwest said. The Associated Press reported cracks were found in three jets.

The April 1 incident on Flight 812 spurred checks of 79 of Dallas-based Southwest's 737-300s. Airlines must make regular checks of their planes for metal fatigue, which can occur as jets endure the stress of takeoffs, landings and low outside air pressure of high-altitude flight, Bloomberg reports.

According to Federal Aviation Administration (FAA) records, the airline in March 2010 identified and fixed 21 cracks in the fuselage of the Boeing 737-300 involved in Friday's incident during a scheduled inspection that lasted more than a week. Outside airline maintenance specialists say such fatigue cracks are not uncommon in older jets.

At that time, the 15-year-old plane had 45,944 flight hours and had gone through about 39,000 cycles of pressurizing, generally done for takeoffs and landings. Cracks can develop from the constant cycle of pressurizing for flight, then releasing the pressure, The Seattle Times reports.