Airworthiness Directives; Twin Commander Aircraft LLC Airplanes

We are adopting a new airworthiness directive (AD) for certain Twin Commander Aircraft LLC Models 690, 690A, and 690B airplanes. This AD requires inspection for cracking of the outer fuselage attachments, the lower wing main spar, the vertical channels, the upper picture window channels, aft cabin pressure web, external wing to fuselage fillets, and fasteners; repair or replacement of damaged parts as necessary; and modification of the structure with reinforced parts. This AD was prompted by cracks found in the upper picture window frame channels, left- and right-hand wing main spar frame support channels, and aft pressure bulkhead web. This condition, if not corrected, could result in structural failure of the airplane. We are issuing this AD to correct the unsafe condition on these products.