Airworthiness Directive · Amendment 39-15815 · Wings
Viking Air Limited Model DHC-6-1, DHC- 6-100, DHC-6-200, and DHC-6-300 Airplanes
This AD applies to the following Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-300 airplanes, all serial numbers, that are certificated in any category:
(1) Group 1: Equipped with wing boxes, part numbers (P/Ns) C6W1002-1, C6W1002-3, WR6-1002-59 or WR6-1002-61 that incorporate a P/N C6WM1027-1 front spar adapter assembly with 10 or more years of service; and
(2) Group 2: Equipped with wing boxes, P/Ns C6W1002-5, C6W1002-7, C6W1002-9, C6W1002-11, C6W1002-13, C6W1002-15, C6W1002-17, C6W1002-19, C6W1002-21, C6W1002-23, C6W1002-51, C6W1002-53, C6W1002-55, C6W1002-57 or C6W1002-61 that incorporate a P/N C6WM1027-1 front spar adapter assembly with 10 or more years of service.
We are superseding an existing airworthiness directive (AD) for the products listed above. This AD results from mandatory continuing airworthiness information (MCAI) issued by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI describes the unsafe condition as:
Unless already done, do the following actions:
(1) For Group 1 airplanes, within the next 180 days after August 5, 2008 (the effective date of AD 2008-11-10), install inspection holes in the left-hand (LH) and right-hand (RH) lower wing skins following Viking DHC-6 Twin Otter Service Bulletin Number V6/541, dated October 1, 2007.
(2) For Group 2 airplanes, within the next 180 days after the effective date of this AD, install inspection holes in the LH and RH lower wing skins following Viking DHC-6 Twin Otter Service Bulletin Number V6/541, dated October 1, 2007.
(3) For Group 1 and Group 2 airplanes, before further flight after installing the inspection holes required in paragraph (f)(1) or (f)(2) of this AD, initially inspect the LH and RH front spar adapter assemblies for cracks, and repetitively thereafter inspect all affected wing box P/Ns at intervals not to exceed 1,200 hours time-in-service or 12 months, whichever occurs first, until the replacement required in paragraph (f)(4) of this AD is done.
(i) For wing box P/Ns C6W1002-1, C6W1002-3, C6W1002-5, C6W1002-7, C6W1002-9, C6W1002-11, C6W1002-13, C6W1002-15, C6W1002-17, C6W1002-19, C6W1002-21, C6W1002-23, C6W1002-51, C6W1002-53, C6W1002-55, C6W1002-57, C6W1002-59, and C6W1002-61, inspect following Viking DHC-6 Twin Otter Service Bulletin Number V6/540, dated October 1, 2007.
(ii) For wing box P/Ns WR6-1002-59 or WR6-1002-61, inspect following R.W. Martin, Inc. Service Bulletin No. 00160/2, Revision A, dated November 15, 2007.
(4) For Group 1 and 2 airplanes, before further flight after doing any inspection required in paragraph (f)(3) of this AD where cracks are found, replace the cracked front spar adapter assembly with a front spar adapter assembly, P/N C6WM1027-3. Do the replacement following Viking DHC-6 Twin Otter Service Bulletin Number V6/542, dated October 1, 2007. This replacement terminates the repetitive inspections required in paragraph (f)(3) of this AD for the replaced front spar adapter assembly.
(5) As a terminating action for the repetitive inspections required in paragraph (f)(3) of this AD, at any time after the initial inspection required in paragraph (f)(3) of this AD, you may replace P/N C6WM1027-1 with P/N C6WM1027-3, except it must be replaced prior to further flight as required by paragraph (f)(4) of this AD.
Note: This AD differs from the MCAI and/or service information as follows: (1) MCAI Transport Canada AD No. CF-2007-31, dated December 17, 2007, is applicable to airplane models with front spar adapter assembly P/N C6WM1027-3 that incorporate task C57-10-18 of the DHC-6 Corrosion Prevention and Control Manual (CPCM), PSM 1-6-5. (2) The applicability of this AD does not include airplane models with front spar adapter assembly P/N C6WM1027-3 that incorporate task C57-10-18 of the DHC-6 CPCM, PSM 1-6-5, which is required in the Transport Canada AD No. CF-94-12R1, dated April 13, 1999, and AD No. CF-99-11, dated May 28, 1999. We have addressed the Corrosion Prevention and Control Program in AD 2008-13-11 (73 FR 37355, July 1, 2008), which identifies specific areas that must be inspected to ensure the structural integrity of the DHC-6 fleet.
