AD 2020-10-05 Requires Disabling The Automatic Temperature Compensation Feature Of The FMS

The FAA is adopting a new airworthiness directive (AD) for certain Rockwell Collins, Inc. (Rockwell Collins) flight management systems (FMS) installed on airplanes. This AD was prompted by reports of the flight management computer (FMC) software issuing incorrect turn commands when the altitude climb field is edited or the temperature compensation is activated on the FMS control display unit. This AD requires disabling the automatic temperature compensation feature of the FMS through the configuration strapping units (CSU) and revising the airplane flight manual (AFM) Limitations section. The FAA is issuing this AD to address the unsafe condition on these products.

This AD is effective June 24, 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 certain part-numbered Rockwell Collins Pro Line 4 and Pro Line 21 FMSs. The NPRM published in the Federal Register on December 6, 2018 (83 FR 62736).

The NPRM was prompted by a flight inspection on a Bombardier Model CRJ-200 airplane, during which Nav Canada, which is Canada's civil air navigation service provider, observed the FMS map displaying an incorrect turn for the Fort St. John airport instrument landing system runway 29 missed approach while using temperature compensation. Nav Canada assumed this was only an issue with the map display and reported the incident to Rockwell Collins. Rockwell Collins subsequently determined that an error in the design of the Pro Line 4 and Pro Line 21 FMC software causes changes to the procedure-defined turn direction when the procedure has been significantly modified.

The FMS removes the planned database turn direction when the flight crew edits the altitude climb field, and the flight crew may not notice the change during climb. The FMS also removes the planned database turn direction if the flight crew uses the temperature compensation to edit the altitude climb field, which may go unnoticed by the flight crew with the increased workload involved with a missed approach procedure. Editing the altitude or using temperature compensation does not change the flight segment. However, due to the design error, the software thinks the flight segment has changed.

The change of the planned turn direction can occur for either left or right turns.

The FMS commanding incorrect turn direction may result in a collision or controlled flight into terrain.

The NPRM proposed to require disabling the automatic temperature compensation feature of the FMS through the CSU and revising the AFM Limitations section. The FAA is issuing this AD to address the unsafe condition on these products.

FMI: www.regulations.gov