AD 2022-05-11 Requires A Bolt Hole Eddy Current Inspection Of The Lug Plate Holes

The FAA is adopting a new airworthiness directive (AD) for Viking Air Limited (type certificate previously held by Bombardier Inc.) Model DHC-3 airplanes with a certain wing strut assembly installed.

This AD results from mandatory continuing airworthiness information (MCAI) originated by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. The MCAI identifies the unsafe condition as fatigue damage of the wing struts. This AD requires a bolt hole eddy current inspection of the lug plate holes, a visual and fluorescent dye penetrant inspection of the lug fittings, and a visual and eddy current surface scan inspection of the wing strut assemblies. This unsafe condition could lead to failure of the wing strut, which could result in an in-flight breakup of the wing. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective April 13, 2022.

Supplementary Information: The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 by adding an AD that would apply to Viking Air Limited (formerly Bombardier Inc.) Model DHC-3 airplanes with a wing strut assembly part number (P/N) C3W100 (all dash numbers) installed. The NPRM published in the Federal Register on December 21, 2021 (86 FR 72198). The NPRM was prompted by MCAI originated by Transport Canada, which is the aviation authority for Canada. Transport Canada has issued AD CF-2020-20, dated May 27, 2020 (referred to after this as “the MCAI”), to correct an unsafe condition on Viking Air Limited (formerly Bombardier Inc.) Model DHC-3 airplanes.

The MCAI states:

• A DHC-3 experienced an in-flight failure of a wing strut in October 2019. Inspection of the failed part determined that it had fractured and that the fracture was consistent with fatigue damage. The investigation of the occurrence is ongoing.
• In 1969, it was determined from fatigue testing and analysis that part number (P/N) C3W100 wing strut assemblies on DHC-3 that were used for normal operations at a maximum weight of 8000 pounds should be removed from service before they have accumulated more than 20 000 hours air time. This information, including definitions of normal operations, was published in Service Bulletin 3/10 dated 26 August 1969. It was also published at the same time in Appendix 4 Part 6, Structural Component Recommended Service Life Limits, of the DHC-3 Maintenance Manual PSM 1-3-2.
• It is Transport Canada Civil Aviation (TCCA) policy to mandate compliance with new or more restrictive airworthiness limitations (AWLs) by the issuance of an AD if the AWL is established after products that are affected by the AWL are already in service. To date, TCCA has not mandated compliance with the 20 000 hours air time life limit AWL that is applicable to P/N C3W100 wing strut assemblies. This AD includes a requirement to comply with the life limit.
• Some DHC-3 aeroplanes have been modified to permit operations at maximum weights above 8000 pounds. For example, TCCA Supplemental Type Certificate (STC) SA95-32 increases the maximum operating weight to 8367 pounds. This STC includes a requirement to reduce the life limit that is applicable to P/N C3W100 wing strut assembly from 20 000 hours air time to 17 500 hours air time, adjusted for the amount of time that the wing strut assembly is used at the higher maximum operating weight. Because this reduced life limit has been in place since the initial issue of STC SA95-32 in 1995, TCCA considers compliance to be mandatory for all aeroplanes that have been modified in accordance with the STC.
• In November 2019, Viking Air Ltd. (Viking) issued Alert Service Bulletin (ASB) V3/0011. The ASB provides instructions for a one-time inspection and follow-on corrective actions for all dash numbers of wing strut assembly P/N C3W100. Since that time, several operators have reported the results of the inspection to Viking. The information in the operators' reports suggests that other DHC-3 wing struts may be at risk of failure. The inspection of the wing struts on five aeroplanes revealed crack indications during non-destructive inspection of bolt holes, seized bolts, pitting corrosion and fretting on the face of lug plates, scratches and gouges in the bolt hole of a lug plate. Failure of a wing strut could result in a catastrophic in-flight breakup of the wing.
• This [Transport Canada] AD mandates the accomplishment of ASB V3/0011 or alternative inspection instructions provided by Viking on wing struts that have accumulated more than 2500 hours air time as of the effective date of this AD. New or serviceable struts installed on aeroplanes after the effective date of this AD that accumulate more than 2500 hours air time after the effective date of this AD are not subject to this AD or to the ASB V3/0011 inspections.

You may examine the MCAI in the AD docket at https://www.regulations.gov by searching for and locating Docket No. FAA-2020-1005.

FMI: www.regulations.gov