Airworthiness Directive · Amendment 39-15350 · Structures
Viking Air Limited Model DHC-6 Series Airplanes
Superseded. A later AD replaced this one: AD 2022-03-04. 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, certificated in any category.
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, within 30 days after March 6, 2008 (the effective date of this AD), for all aircraft, incorporate the inspections, modifications, and/or retirement of components specified in Bombardier Inc.(formerly de Havilland) DHC-6 “Twin Otter” PSM 1-6-11, Revision 6, dated March 28, 2007, into the aircraft maintenance program. The compliance times are specified in the manual. For aircraft that are approaching or have exceeded the threshold of the new or revised inspections introduced by this AD, compliance with the threshold inspection may be modified as detailed below:
(1) Pre Mod 6/1117 Wing Assemblies:
(i) If the last inspection done of the main wing spar attachment lug fastener holes, before March 6, 2008 (the effective date of this AD), was an eddy current inspection following Bombardier Inc. (formerly de Havilland) DHC-6 “Twin Otter” PSM 1-6-11, Revision 5, dated January 11, 2000; or PSM 1-6-11, Revision 6, dated March 28, 2007; do the repeat high frequency eddy current inspection in accordance with the schedule in PSM 1-6-11, Revision 6, dated March 28, 2007.
(ii) If the last inspection done of the main wing spar attachment lug fastener holes, before March 6, 2008 (the effective date of this AD), was an ultrasonic inspection following Bombardier Service Bulletin 6/525, dated September 6, 1996, do the first high frequency eddy current inspection within 1,000 hours time-in-service (TIS) or 2000 cycles, whichever occurs first, after the last ultrasonic inspection. Repetitively inspect thereafter in accordance with the schedule in PSM 1-6-11, dated March 28, 2007.
Note 1: Operators that do not have landing (or cycle) records may determine the number of landings (or cycles) by dividing the number of hours of time-in-service of each airplane by the time of the average flight for the aircraft of that type in the operator's fleet.
(2) Post Mod 6/1117 and Post Mod 6/1630 Wing Assemblies: If the inspection threshold for the lower wing skin, stringers, and aft spar lower flange WS122 to WS263 (ribs 8 to 20) has been exceeded or will be exceeded within 6 months after March 6, 2008 (the effective date of this AD), do the first high frequency eddy current inspection within the next 500 hours TIS after March 6, 2008 (the effective date of this AD), or within the next 6 months after March 6, 2008 (the effective date of this AD), whichever occurs first, following PSM 1-6-11, Revision 6, dated March 28, 2007.
(g) You may take “unless already done” credit if the above actions were done following the procedures described in Bombardier Inc. (formerly de Havilland) DHC-6 “Twin Otter” PSM 1-6-11, Revision 5, dated January 11, 2000.
Note 2: This AD differs from the MCAI and/or service information as follows: The MCAI references PSM 1-6-11, Revision 5, dated January 11, 2000. PSM 1-6-11, Revision 6, dated March 28, 2007, has since been issued and is referenced for compliance in this AD.
