COMMONWEALTH OF AUSTRALIA (Civil Aviation Regulations 1998), PART 39 - 105 CIVIL AVIATION SAFETY AUTHORITY
SCHEDULE OF AIRWORTHINESS DIRECTIVES
Bell Helicopter Textron 412 Series Helicopters
AD/BELL 412/35 Tail Boom Doubler and Fin Spar Caps 5/95
Applicability: Bell 412 helicopters S/N 33001 to 33213, 34001 to 34024 and 36001 to 36071. The Serial Numbered Tail Booms listed in Bell Alert Service Bulletin (ASB) 412-93-74 Revision A are not subject to the requirements of this AD.
Requirement: 1. Conduct detailed visual and sonic internal inspections of the fin spar caps P/N 212- 030-447-001 and -101, tail boom upper longerons, skin and doubler P/N412-030- 117-101, in the vicinity of the vertical fin, in accordance with Bell Alert Service Bulletin (ASB) 412-93-74 Revision A, Accomplishment Instructions Part I(A) and (B).
2. Replace fin spar caps with P/N 212-030-447-117S. Remove doubler P/N 212-030- 099-089/129 and rebond in place in accordance with Bell ASB 412-93-74 Revision A, Accomplishment Instructions Part II.
Compliance: 1. a. Initially inspect fin spar caps P/N 212-030-447-001 within 25 hours time in service after 27 April 1995.
1. b. Initially inspect fin spar caps P/N 212-030-447-101 before 1000 hours component time in service or within 25 hours time in service after 27 April 1995, whichever is the later.
1. c. Re-inspect the fin spar caps (both part numbers) at intervals not to exceed 25 hours time in service until modified in accordance with Requirement 2.
- d. Inspect the upper longerons, skin and doubler within 25 hours time in service after 27 April 1995 or before 26 July 1995, whichever occurs first. Re-inspect at intervals not to exceed 100 hours time in service until modified in accordance with Requirement 2.
2. Replace parts and re-install the doubler in accordance with Requirement 2 before 27 January 1996.
Background: Bell 412 operators have reported cracks in the fin left hand spar caps in both the hot and cold bonded configurations. Cracks have also been reported in upper longerons and tail boom upper skin. The problem was due to lack of adhesive, or the incorrect adhesive, in the doubler-skin bonded joint.