1AD/HILLER 12/29 Amdt 4 - Main Drive Torsion Coupling - Inspection and Replacement

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 12/29

Amdt 4

Main Drive Torsion Coupling - Inspection and Replacement

11/84

Applicability: All Hiller models fitted with Torsion couplings Part Number 21046-5, 21047-9, 21047-11.

Requirement: 1. (a) Inspect the torsion coupling in accordance with Hiller Service Manual Section 21-2-42, para. “C”. In addition, inspect the mating surfaces between the upper and lower halves of the torsion coupling for indications of relative movement between the surfaces.

(b) Inspect the six upper coupling mounting studs for cracking and wear, and the upper coupling flange holes for elongation.

(c) Ensure that a zero clearance fit exists between the upper mounting studs and flange holes. It should be necessary to use the flange jack screw holes to separate the upper and lower sections.

(d) Remove from service any coupling with indications of movement between surfaces, damaged studs, or clearance between studs and holes.

2. Remove from service all P/N 21047-9 or 21047-11 couplings with serial numbers 497 through 766.

Note: The dimensional criteria given in Hiller SB UH-12-21-1 is no longer valid.

Compliance: 1. For para. 1 of the requirement document - before installation of a coupling, and thereafter at periods not exceeding 300 hours’ time in service.

2. For para. 2 of the requirement document - within 100 hours’ time in service after 31 July 1982.

Background: This Directive is raised in issue to amend the applicability to include specific Part Numbered Torsion couplings only.