AD 2021-10-13 Prompted By A Report Indicating That Several Failure Modes Of The NWS System May Cause Loss Of Feedback

The FAA is superseding Airworthiness Directive (AD) 2015-17-08, which applied to certain Bombardier, Inc. Model DHC-8-400 series airplanes.

AD 2015-17-08 required installing new cable assemblies with a pull-down resistor. This AD requires modifications to the nose wheel steering (NWS) system. This AD was prompted by a report indicating that several failure modes of the NWS system may cause the loss of feedback from both rotary variable differential transformers to the steering control unit. The FAA is issuing this AD to address the unsafe condition on these  products. This AD is effective July 1, 2021.

Supplementary Information: Transport Canada Civil Aviation (TCCA), which is the aviation authority for Canada, has  issued TCCA AD CF-2020-28, dated August 14, 2020 (also referred to as the Mandatory Continuing Airworthiness Information, or the MCAI), to correct an unsafe condition for certain De Havilland Aircraft of Canada Limited Model DHC-8-401 and -402 airplanes. You may examine the MCAI in the AD docket on the internet at www.regulations.gov by searching for and locating Docket No. FAA-2021-0018.

The FAA issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to supersede AD 2015-17-08, Amendment 39-18241 (80 FR 51459, August 25, 2015) (AD 2015-17-08). AD 2015-17-08 applied to certain Bombardier, Inc. Model DHC-8-400 series airplanes. The NPRM published in the Federal Register on February 24, 2021 (86 FR 11175). The NPRM was prompted by a report indicating that several failure modes of the NWS system may cause the loss of feedback from both rotary variable differential transformers to the steering control unit. The NPRM proposed to require modifications to the NWS system. The FAA is issuing this AD to address failure modes of the NWS system, which could lead to NWS runaway, loss of directional control of the airplane, and possible consequent runway excursion. See the MCAI for additional background information.

FMI: www.regulations.gov