AD 2021-08-07 Prompted By An Un-Annunciated GPS Position Error

The FAA is adopting a new airworthiness directive (AD) for certain Rockwell Collins, Inc. (Rockwell Collins), GPS-4000S Global Positioning Systems (GPS) installed on airplanes.

This AD was prompted by an un-annunciated GPS position error, which could cause a misleading localizer performance with vertical guidance (LPV) glidepath, resulting in controlled flight into terrain (CFIT). This AD requires upgrading the GPS-4000S. The FAA is issuing this AD to address the unsafe condition on these products. This AD is effective May 12, 2021.

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 Rockwell Collins GPS-4000S GPS installed on airplanes. The NPRM published in the Federal Register on October 29, 2020 (85 FR 68501). The NPRM was prompted by the FAA being notified of a software error in GPS P/N 822-2189-100 that can result in an unannunciated inaccurate GPS position in the region within approximately 1,000 miles (+/-20 degrees) of 180 degrees west longitude. The software improperly applies the wide area augmentation system ionospheric delay corrections to the GPS signal from satellites located across the 180th meridian. Due to this anomaly, the position accuracy may be diminished such that the GPS-4000S P/N 822-2189-100 will not support LPV approaches in the affected region. In the NPRM, the FAA proposed to require removing P/N 822-2189-100 GPS-4000S GPS from the airplane and installing P/N 811-2189-101 GPS-4000S GPS. The FAA is issuing this AD to prevent a misleading glidepath on an affected LPV approach, resulting in CFIT.

FMI: www.regulations.gov