The carrier detected the crack while the aircraft was recently undergoing other maintenance at its Alliance Fort Worth maintenance base, says the airline.
American then brought the issue to the US Federal Aviation Administration's attention, and the regulator and airline worked out an inspection schedule that spanned a week-and-a-half for a total of 56 aircraft - 15 767-200s and 41 767-300s. The carrier says that 17 of American's total fleet of 58 767-300s were excluded from the inspections since they are newer model aircraft with a different pylon configuration.
The inspections were carried out during overnight line maintenance at stations across the carrier's system, and cracks were discovered on a total of two aircraft, including the first aircraft that triggered the inspections.
Boeing, meanwhile, confirms that an operator has found cracking on the 767 strut midspar ahead of an inspection interval featured in a manufacturer service bulletin and FAA airworthiness directive.
The airframer says it is "moving toward issuing a revised service bulletin on this matter that will call for a change to the recommended inspection interval for the strut midspar".