Fuel Imbalance — Inflight

Gulfstream GVII

Eddie sez:

Fuel imbalance procedures have not changed since the airplane was initially certified but when you are allowed to balance the fuel has. In a nutshell: don't do anything until you get a CAS message saying you have an imbalance.

Everything here is from the references shown below, with a few comments in an alternate color.

Last revision:

20191019

AFM Procedure

[G500-MOL-19005, §01-28-40] Fuel Balancing is prohibited in flight unless the displayed fuel imbalance is greater than 1,000 lbs and a Fuel Imbalance CAS message is displayed.

[AFM, §03-14-20]

Possible Cause

The fuel imbalance is greater than 2000 lbs.

Corrective Action

    NOTE

    If a fuel imbalance annunciates via CAS shortly after a change in aircraft pitch with no other reasonable cause, the imbalance should be considered erroneous.

  1. If fuel imbalance cause is known:

    1. Refer to 02-08-60, Fuel Balancing in Flight.

  2. If fuel imbalance cause is unknown:

    1. CMC . . . Select

    2. Maintenance Messages / Active / ATA 28 . . . Select

    3. FQM CH CHAIN OVERCURRENT LIMIT . . . Verify not displayed

    4. FQSC PROBE FAILED . . . Verify not displayed

    5. If CMC fuel maintenance indications are displayed:

    6. (1) Autopilot . . . Disconnect

      (2) Aircraft . . . Trim wings level (no roll rate)

      (3) Roll Trim . . . Verify within 1/4 of 1 roll-trim unit

      (4) If Roll Trim exceeds 1/4 unit:

      (a) Refer to 04-14-10, Fuel Leak in Flight.

      (5) If Roll Trim is within limits:

      NOTE

      FMS fuel quantity should not be updated in flight. The FMS fuel quantity is an independent information source provided to verify FQMS quantity and assist troubleshooting FQMS indication errors or fuel leaks.

      (a) FMS Fuel Quantity (TSC/FMS/ Perf Init) . . . Check

      (b) Flight Planning . . . Use lower of FQMS or FMS displayed value

      (c) Fuel Balancing . . . Do not attempt

      (d) Autopilot . . . As required

    7. If CMC fuel maintenance indications are not displayed:

    8. (1) Refer to 04-14-10, Fuel Leak in Flight.


Gulfstream GVII-G500 Airplane Flight Manual, Revision 4, August 29, 2019

Gulfstream GVII-G500 Maintenance and Operations Letter, G500-MOL-19-0005, Fuel (ATA 28) AFM Supplement to Address Erroneous Fuel Quantity Display and Fuel Imbalance Crew Alerting System Message, June 19, 2019

Gulfstream GVII-G500 Production Aircraft Systems, Revision 3, July 15, 2019