AD 2020-12-06 Prompted By Reports Of Uncommanded Nose Wheel Steering Turns

The FAA is adopting a new airworthiness directive (AD) for all Gulfstream Aerospace Corporation (Gulfstream) Model G-IV airplanes. This AD was prompted by reports of uncommanded nose wheel steering turns.

This AD requires replacing the nose wheel steering servo valve manifold, incorporating revised operating procedures into the airplane flight manual (AFM), doing a records inspection for any incidents of un-commanded nose wheel steering turns, and reporting the results to the FAA. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective July 20, 2020.

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 all Gulfstream Model G-IV airplanes. The NPRM was published in the Federal Register on December 27, 2019 (84 FR 71333). The NPRM was prompted by reports of uncommanded nose wheel steering turns. An investigation revealed the supplier compromised the seals during assembly of the electro-hydraulic servo valves, which allows moisture to enter the valve.

During cold soak conditions, the moisture forms ice crystals in the servo valve armature air gaps, which may cause the valve armature to displace to a non-neutral position. This condition, if not addressed, could result in an un-commanded nose wheel position once power is applied to the nose wheel servo and subsequent lateral runway departure. To address this condition, the supplier improved their production quality control process to reduce the risk of compromised seals in the nose wheel steering servo valve. Gulfstream also revised the normal, abnormal, and emergency procedures in the AFMs related to nose wheel steering un-commanded turns.

Accordingly, this AD requires replacing the nose wheel steering servo valve manifold, incorporating revised operating procedures into the AFM, doing a records inspection for any incidents of un-commanded nose wheel steering turns, and reporting the results to the FAA. The FAA is issuing this AD to address the unsafe condition on these products.

FMI: www.regulations.gov