There have been a number of accidents and near accidents because pilots didn't understand a fuel imbalance was actually an indication of fuel leaking from an engine. In one case, they thought it was a computer problem. (See Air Transat 236.) In another (unpublished) incident with a entry into service test flight, the crew thought they could make to the airport before they ran out of gas; they landed with less than a thousand pounds. The lesson: just because you can't see the fuel leaking doesn't mean it isn't.
Everything here is from the references shown below, with a few comments in an alternate color.
DO NOT PERFORM THIS PROCEDURE ON THE BASIS OF ERRATIC FUEL GAUGE INDICATIONS ONLY OR DURING ASYMMETRIC TRIM REQUIREMENTS FELT DURING ACCELERATING PHASES OF FLIGHT SUCH AS INITIAL CLIMB OR NOSE HIGH OR NOSE LOW PITCH ATTITUDES.
A suspected fuel leak will most likely manifest itself as an increasing difference in fuel quantity that cannot be explained by normal differences in fuel flows between engines. It can also be identified by fuel smell in the cabin, abnormally high fuel flow or fuel flow out of range indications on one of the engines, or lateral trim changes.
Identify leak by observing one wing fuel tank quantity decreasing faster than the other, and or slowly increasing lateral trim force.
THIS PROCEDURE MAY RESULT IN ENGINE FAILURE.
(1) The leak should be assumed to be in the affected side wing fuel tank. Go to Step 9.
(1) FUEL CONTROL (Affected Engine) . . . OFF
(2) FIRE Handle (Affected Engine) . . . Pull (Do Not Rotate)
(3) GEN (Affected Engine) . . . OFF
(4) ENG BLEED AIR (Affected Engine) . . . OFF
(5) Isolation Valve . . . Open (Depressed)
(6) TCAS . . . TA only
(7) MAIN FUEL PUMP and ALT FUEL PUMP (Affected Engine) . . . Verify Off
(8) FUEL CROSSFLOW . . . Verify Closed
The APU may be used as an alternate source of electrical power, if desired. Refer to 03-03-10, APU Inflight Operation - Alternate Electrical Power Source.
(9) Fuel Balance Maintain utilizing Intertank Valve
(a) Refer to 02-08-60, Fuel Balancing in Flight.
(10)Airplane Land as soon as possible
Refer to 04-08-30, One Engine Inoperative Landing Procedure.
THE FLIGHT CREW MUST EVALUATE THE FUEL LOSS RATE AND DISTANCE TO NEAREST SUITABLE LANDING AIRFIELD. CONSIDERATION SHOULD BE GIVEN TO TWO-ENGINE VERSUS SINGLE-ENGINE CLIMB TO ALTITUDE IN ORDER TO ACHIEVE GREATER RANGE, MAXIMUM TRANSFER OF FUEL TO GOOD TANK VERSUS LATERAL CONTROLLABILITY, AND AFFECTED SIDE ENGINE FAILURE DUE TO FUEL STARVATION.
Up to 4000 lbs of fuel imbalance between tanks while in flight has been safely demonstrated in flight under abnormal conditions.
For approach and landing with abnormal fuel imbalance and an engine shut down, be prepared to use full rudder and aileron as required.
IF FUEL INTERTANK VALVE IS USED FOR MAXIMUM FUEL TRANSFER RATES, ENSURE PROPER SIDESLIP IS MAINTAINED TO PREVENT FUEL FROM FLOWING BACK INTO LEAKING TANK. APPLY RUDDER TRIM IN THE DIRECTION OF LEAKING TANK.
DO NOT USE THRUST REVERSERS ON LANDING.
Gulfstream GVII-G500 Airplane Flight Manual, Revision 4, August 29, 2019
Gulfstream GVII-G500 Production Aircraft Systems, Revision 3, July 15, 2019
Copyright 2019. Code 7700 LLC. All Rights Reserved.