WEBAug 7, 2021 · The Federal Aviation Administration issued AD (airworthiness directive) 2021-08-07 on April 7, 2021, that impacts aircraft with the Rockwell Collins GPS-4000S (P/N 822-2189-100) installed. This AD was prompted by an un-annunciated GPS vertical error that could result in a hazardously misleading LPV glidepath.