Primary Flight Display Symbols
Check Altimeter Annunciation
The CHECK ALT annunciation appears in amber to indicate the difference between both PFDs altitude indications is greater than 250 feet (QNH), or 500 feet (STD).
In RVSM airspace, both primary altimeters must agree within 200 feet at all times. At intervals of approximately one hour, or when passing oceanic waypoints, confirm the primary altimeters are within the 200-foot tolerance.