AD 2022-11-12 Requires Performing Tests, Inspections, And Lubrication Of The FCU Push Rod Assemblies

The FAA is adopting a new airworthiness directive (AD) for certain Viking Air Limited (type certificate previously held by Bombardier Inc. and de Havilland, Inc.) Model DHC-6-1, DHC-6-100, DHC-6-200, DHC-6-300, and DHC-6-400 airplanes.

This AD was prompted by 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 binding of the rod end bearing connecting the lower fuel control unit (FCU) push rod assembly to the FCU power lever. This AD requires performing tests, inspections, and lubrication of the FCU push rod assemblies, and replacing them with improved parts as necessary. The FAA is issuing this AD to address the unsafe condition on these products.  DATES: This AD is effective July 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 certain serial-numbered Viking Air Limited Model DHC-6-1, DHC-6-100, DHC-6-200, DHC-6-300, and DHC-6-400 airplanes. The NPRM published in the Federal Register on March 22, 2022 (87 FR 16123). The NPRM was prompted by MCAI originated by Transport Canada, which is the aviation authority for Canada. Transport Canada has issued AD CF-2021-42, dated November 26, 2021 (referred to after this as “the MCAI”), to correct an unsafe condition on Viking Air Limited Model DHC-6 series 1, DHC-6 series 100, DHC-6 series 110, DHC-6 series 200, DHC-6 series 210, DHC-6 series 300, DHC-6 series 310, DHC-6 series 320, and DHC-6 series 400 airplanes with certain part-numbered FCU push rod assemblies installed.

The MCAI states: 

• There have been in-service reports of binding of [part number] P/N VSC30-3A rod end bearings used in the linkage for the lower FCU push rod assembly P/N C6CE1398-7. The lower FCU push rod assembly is connected to the FCU power lever and contains a rod end bearing at each end. P/N VSC30-3A rod end bearings, fabricated with a metal inner race and a dry film lubricant, have been incorporated on FCU push rod assemblies introduced through Viking Air Ltd (Viking) MOD 6/2347. P/N VSC30-3A rod end bearings may have also been installed in-service as a replacement part in lower FCU push rod assembly P/N C6CE1398-3. In one instance, binding of the lower FCU push rod bearing resulted in one engine failing to return to a lower power setting from a higher power setting when commanded, which subsequently resulted in the need to perform an in-flight engine shutdown during final approach. An investigation also revealed that binding of P/N VSC30-3A rod end bearings can occur after a period of non-utilization of the aeroplane. 
• This condition, if not detected and corrected, may lead to the inability to reduce power on the affected engine, resulting in the need to perform an in-flight engine shutdown, and consequently leading to reduced control of the aeroplane and increased pilot workload during this critical phase of flight. 
• To address this unsafe condition, this [Transport Canada] AD mandates initial and repetitive functional checks, special detailed inspection (SDI) and lubrication of the affected FCU push rod assembly, and its replacement, as required, with a redesigned FCU push rod assembly with improved reliability (MOD 6/2484), in accordance with Viking Service Bulletin (SB) V6/0063. This [Transport Canada] AD also prohibits the 3 installation of an affected FCU push rod assembly as a replacement part on applicable aeroplanes.  

You may examine the MCAI in the AD docket at https://www.regulations.gov by searching for and locating Docket No. FAA-2022-0284.

In the NPRM, the FAA proposed to require performing tests, inspections, and lubrication of the FCU push rod assemblies, and replacing them with improved parts as necessary. The FAA is issuing this AD to address the unsafe condition on these products.

FMI: www.regulations.gov