Document ID: chunk:federal_register_of_legislation:F2006B06460:body:0:p2
Version: federal_register_of_legislation:F2006B06460
Segment Type: other
Provision Reference: 
Character Range: 2795–4087

and felt severe vibrations while hovering, resulting in a forced landing. Upon inspection, a crack was found in a main rotor blade that started at the mid-span inboard trim tab and ran chordwise to the spar where it turned along the spar for about an inch. The crack originated from a trim tab alignment rivet hole in the blade skin.

           Subsequent investigations revealed that the manufacturing process utilised to drill the trim tab alignment rivet holes in the main rotor blade skin can allow a fatigue crack to originate at these holes and propagate in the skin. This condition, if not corrected, could result in failure of the main rotor blade and subsequent loss of control of the helicopter.

           This amendment adds a requirement to replace the affected main rotor blades. Examination of the cracked main rotor blade has indicated that a crack may develop in any of the affected blades. As it has not been possible to determine how quickly the crack progressed, it is not possible to maintain the airworthiness of the blade through inspection. It is therefore necessary to remove the affected main rotor blades from service.

           The initial issue of this Airworthiness Directive became effective on 5 June 1998.

                                      Figure 1