The agency's telegraphic Airworthiness Directive (AD) follows two June 26 inflight engine shutdowns, one on Transaero Airlines, Russia, and the other on Braathens Airlines, Norway. There were no injuries. In both incidents, the accessory gearbox starter gearshaft failed due to inadequate fatigue capability caused by high stresses introduced during the manufacturing process. A lack of shotpeening, a manufacturing process that relieves stress and prevents fatigue cracks in the gearshaft hub, was the primary cause of the failures. CFM has modified the manufacturing process.

Prior to further flight, the AD requires immediate inspection of the magnetic chip detector on the No. 2 engine on all Boeing 737-700 and -800 aircraft. The operator is required to remove and replace the starter gearshaft if the detector finds abnormal magnetic particles. The No. 1 engine must be inspected the following calendar day. The agency is requiring further inspections of both engines every other day. All No 2. engine starter gearshafts must be replaced by August 1, or within 350 hours time in service, whichever occurs first. All No.1 engine gearshafts must be replaced by Sept. 1, or within 725 hours, whichever occurs first.

The magnetic chip detector inspection takes a half-hour to complete and costs $30 per engine. A gearshaft replacement takes 12 hours to complete and costs approximately $9,575 for parts, $10,295 total per engine.

Worldwide, there are 94 engines installed on 47 aircraft affected by the AD. Of those, there are 46 engines on 23 U.S. registered aircraft. The total cost for U.S. operators is approximately $535,670. The U.S. operators are Continental Airlines (9 aircraft), Southwest Airlines (13 aircraft), and Eastwind Airlines (one aircraft).