An emergency airworthiness directive (AD 2003-19-51) was issued Sept. 17 by the Federal Aviation Administration requiring operators of the Cl-600, CL-600-2C10, and Series 700 regional jets to inspect main landing gear doors for cracking, deformation, pulled fasteners, and repair or replace same if found cracked.

The AD may be unusual in that it is based on one instance, where the right main landing gear door of a CL-600-210C Series 700 regional jet "departed the airplane during landing," damaging the trailing edge flap and puncturing the skin in the rear fuselage.

Cracking was found on the door's hinge lug, hence the AD.

Operators of aircraft with less than 1,500 flights must inspect the doors before 1,050 flights or, if past that threshold, within 50 flights. Operators of aircraft with more than 1,500 flights must inspect their aircraft within 10 flights.

Inspection results must be reported to manufacturer Bombardier [Toronto: BBDa.TO]. According to the manufacturer, service bulletins and kits have been shipped to all operators of the affected aircraft to make repairs.

The premature failure appears to relate to the fasteners used, their spacing and the gauge of the metal in that area. The gear doors are subject to aerodynamic forces and vibration. Bombardier's repair consists of reinforcing doublers. The emergency AD was described as an interim action. Stay tuned.