1AD/HILLER 12/42 - Main Rotor Mast

COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY

SCHEDULE OF AIRWORTHINESS DIRECTIVES

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Hiller UH-12 Series Helicopters

AD/HILLER 12/42 Main Rotor Mast 6/91 DM

Applicability: All models.

Requirement: Perform a detailed visual inspection of the main rotor mast at both ends of the two elongated collective control terminal pin slots.

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Compliance: Prior to further flight unless accomplished within the previous 100 hours’ time in service, and thereafter at intervals not to exceed 100 hours’ time in service, and immediately upon the onset of any unusual vibration or any stiffness or binding of the collective control.

Background: Two aircraft have recently been reported as having cracks emanating from the ends of the elongated slots. One aircraft was reportedly cracked through 75% of its cross section while the other was reported to have two cracks 50 mm long. Indications in the worst affected aircraft included lateral and vertical vibration and stiffness and binding of the collective pitch control.

“Emergency Airworthiness Advice for Hiller UH-12 Helicopter” refers.

COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY

SCHEDULE OF AIRWORTHINESS DIRECTIVES