GPS page in FMC

1st Official Post

    Whilst updating for the beta, I added IRS drift and GNSS updating. Everything works perfectly according to the FCOM. I have noticed that, unlike the A320, the A350 GNSS page is incomplete. Are we blocked from adding pages? Nothing I seem to do will get GNSS 1 & 2 to display on the GNSS page


    Full list of what has been added along with the PRIM/SEC rebuild

    Display Spoiler
    • Three independently simulated inertial reference systems: IRS 1, IRS 2 and IRS 3.
    • Each IRS now accumulates its own positional drift rather than remaining permanently locked to the aircraft's true position.
    • Current normal drift rates
      • IRS 1: approximately 0.12 NM/hour
      • IRS 2: approximately 0.17 NM/hour
      • IRS 3: approximately 0.23 NM/hour
    • The IRS units can therefore gradually disagree with each other during a long flight.
    • Drift begins once the respective IRS has completed alignment and enters NAV.
    • Drift continues while the aircraft is on the ground, during taxi, in flight and after landing
    • Re-aligning/leaving NAV resets the accumulated simulated drift.

    • The original IRS ALIGNED ON GNSS POS remains the alignment reference while the individual inertial position can subsequently move away from it.


    GPIRS / GNSS Correction

    • The individual IRS position and the GPIRS navigation solution are now treated separately.
    • With GNSS available, individual IRS units can continue drifting while the GPIRS solution remains GNSS-corrected.
    • A single working GNSS receiver is sufficient to retain satellite position correction.
    • Losing GNSS 1 alone therefore does not result in GPS PRIMARY LOST.
    • Losing GNSS 2 alone also leaves the remaining GNSS receiver available.
    • With both GNSS receivers lost, GNSS correction is removed and the GPIRS solution can transition onto the inertial solution and begin accumulating positional error.

    Independent GNSS Receiver Failures

    Two individual GNSS receiver failure channels have been added:

    • GNSS 1 FAULT
    • GNSS 2 FAULT
    • GNSS 1+2 FAULT
    • Both GNSS healthy → consolidated GPIRS, ~15 m accuracy.
    • One GNSS failed → surviving receiver keeps the position corrected.
    • Both GNSS failed + radio updating available → change to IRS/DMR etc.; position degradation stays relatively controlled.

    • Both GNSS failed + no usable radio update → IRS mode; GPIRS/FMS position then follows the accumulating inertial error and EPU steadily rises.