Southwest reports more cracks

They have been detected on a third 737-300 - subsurface cracks similar to the ones found on the aircraft that split open on Friday. The airline has canceled 70 flights today out of 3,400, although 57 of the 79 aircraft inspected since Friday have returned to service. With so many flights each day, Southwest carries a lighter passenger load than other carriers, and that makes rescheduling a little easier. Meanwhile, the WSJ's Scott McCartney says that the cracking could trigger inspections all over the globe:

Cracks in the aluminum skin of airplanes are routine. Planes are regularly inspected for cracks and repairs are made. If you ever get up close to an older airplane, you can easily see plates of metal called "doublers'' that are attached over cracks. But according to reports from National Transportation Safety Board investigators, the cracks that likely led to a large hole in the roof of a middle-aged Southwest jet on Friday came from the underside of a joint where two pieces of metal overlap one another. The riveted joints run the length of the plane and are not subjected to routine extensive checks. That will mean new inspections for older 737s worldwide.

There are more than 700 737-300s in service today, 169 of them belonging to Southwest.