Airworthiness Directive · Amendment 39-15532 · Wings
Viking Air Limited Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-300 Airplanes
Superseded. A later AD replaced this one: AD 2009-04-09. Comply with the one in force.
This AD applies to Models DHC-6-1, DHC-6-100, DHC-6-200, and DHC-6-300 airplanes, all serial numbers, that are:
(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) Certificated in any category.
We are adopting a new 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) Within the next 180 days after August 5, 2008 (the effective date of this AD), 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) Before further flight after installing the inspection holes required in paragraph (f)(1) of this AD, inspect the LH and RH front spar adapter assemblies for cracks. For wing box P/Ns C6W1002-1 and C6W1002-3, inspect following Viking DHC-6 Twin Otter Service Bulletin Number V6/540, dated October 1, 2007. For wing box P/Ns WR6-1002-59 and WR6-1002-61, inspect following R.W. Martin, Inc. Service Bulletin No. 00160/2, Revision A, dated November 15, 2007. Repetitively inspect all affected wing box P/Ns thereafter at intervals not to exceed 1,200 hours time-in-service or 12 months, whichever occurs first, until the replacement required in paragraph (f)(3) of this AD is done.
(3) Before further flight after doing any inspection required in paragraph (f)(2) 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)(2) of this AD for the replaced front spar adapter assembly.
(4) As a terminating action for the repetitive inspections required in paragraph (f)(2) of this AD, at any time after the initial inspection required in paragraph (f)(2) of this AD, you may replace P/N C6WM1027-1 with P/N C6WM1027-3.
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, requires incorporating task C57-10-18 of the DHC-6 Corrosion Prevention and Control Manual (CPCM), PSM 1-6-5, within 90 days after the effective date of this AD.
(2) We are not incorporating task C57-10-18 of the DHC-6 CPCM, PSM 1-6-5, into this AD because we are currently examining Transport Canada AD No. CF-94-12R1, dated April 13, 1999, and AD No. CF-99-11, dated May 28, 1999. Transport Canada issued these ADs to incorporate a Corrosion Prevention and Control Program that identifies specific areas that must be inspected to ensure the structural integrity of the DHC-6 fleet.
