Summary
The FAA proposes to adopt a new airworthiness directive (AD) for certain Bombardier Model DHC-7 series airplanes. This proposed AD would require revising the Airworthiness Limitations section of the Instructions of Continued Airworthiness to include a new lower life limit for lower wing skins. This proposed AD is prompted by the discovery that during the manufacture of the lower wing skins, score marks may have been accidentally inscribed around the edge of the lower wing skin doublers. We are proposing this AD to prevent fatigue cracks from developing at the score marks in the lower wing skins, which could result in the structural failure of the wing.