Last month, American announced it had found cracks near the pylons that attach the engine to the wing on three Boeing 767s from American's fleet. The FAA then ordered American to inspect several dozen aircraft, and has now expanded that inspection to cover 138 aircraft at multiple airlines operating in the U.S.
Affected airlines include American, Continental, Delta, United, and US Airways.
Part of the concern (aside from the threat of engines falling off planes) is that the cracks appeared suddenly and quickly. When the cracks initially appeared on those American planes, the FAA noted that the cracks appeared at a faster pace than the inspections. As a result, this new inspection order is essentially an acceleration of the existing inspection procedure. According to the Associated Press (AP), airlines now have to inspect their planes every 400 flights or 90 days, whichever is later, instead of every 1,500 flights.
The problem was initially discovered in 2005, at which point the 1,500-flight-inspection order was put in place. Boeing changed its design, and since then its 767s have been problem-free.