Airworthiness Directives; De Havilland Aircraft of Canada Limited (Type Certificate Previously Held by Bombardier, Inc.) Airplanes

The FAA is superseding Airworthiness Directive (AD) 2020-04- 20, which applied to certain De Havilland Aircraft of Canada Limited Model DHC-8-400 series airplanes. AD 2020-04-20 required repetitive inspections of certain parts for discrepancies that meet specified criteria, and replacement as necessary; repetitive inspections of certain parts for damage and wear, and rework of parts; and electrical bonding checks of certain couplings. AD 2020-04-20 also required revising the existing maintenance or inspection program, as applicable, to incorporate new or more restrictive airworthiness limitations. For certain airplanes, AD 2020-04-20 allowed a modification that terminates the repetitive inspections. This AD continues to require the actions in AD 2020-04-20, revises the applicability by adding airplanes, and requires, for certain airplanes, the previously optional rework and retrofit of certain parts of the fuel system. Doing the rework and retrofit terminates the retained initial and repetitive inspections in this AD. This AD was prompted by reports of wear on fuel couplings, bonding springs, and sleeves as well as fuel tube end ferrules and fuel component end ferrules, and by a determination that a more robust lightning ignition protection design is necessary. The FAA is issuing this AD to address the unsafe condition on these products.