Fuel Transfer Using Intertank System - Code7700

Breakfast MinutesMarch 9, 2007 - Volume 14, Issue 32All Large-Cabin (ATA 28): Fuel Transfer Using Intertank SystemBy Branko Stropnik, Service EngineeringEditor: Due to recent operational issues, we are republishing this article from the 6/23/06Breakfast Minutes on the fuel transfer system.Several operators have questioned the operation of the Gulfstream intertank fuel transfer systemand the relationship with the vortex generators (VGs) that are located in front of the NACAscoop on the wing lower surface. The VGs are installed in initial phase/production onG350/G450 and G500/G550 models, and per GIV Aircraft Service Change (ASC) 461, GV ASC159, and G500/G550 ASC 039.To date, we have found no significant effect on wing fuel transfer rates from the installed VGsand only minor fuel tank system defects were found during evaluation of customer aircraft.Engineering and Flight Operations have since worked with several operators concerning the fueltransfer issues and found misconceptions exist regarding the intertank system and the procedurefor transferring fuel between left and right fuel tanks.The following explanation is provided on how the intertank system functions:Misconception: Straight and Level FlightFact: All aircraft indications have a +/- tolerance. Even with a cockpit indication of straight andlevel, some heading, pitch, and roll deviations exist that result in an imperceptible (to the crew)lateral acceleration that will influence the rate and direction of fuel transfer when using theintertank valve.Fact: The same is true of ground operations. Even with an apparent level aircraft, some pitch androll deviation may be present that will send the fuel into the downside wing.Misconception: When opening the intertank valve during level flight, fuel will flow to the wingwith the lower quantity of fuel.Fact: Since the intertank system connects the left and right hoppers, actual fuel quantity has littleeffect on the direction of fuel transfer. The large-cabin Gulfstream fuel system is designed toensure the fuel hopper in the wing is overflowing with fuel at all times the boost pumps areoperating.Under most phases of flight, fuel transfer will initiate not to the under-filled wing but in thedirection of a pre-existing lateral acceleration or to a hopper that is not being maintained atoverflow. This may or may not coincide with the existing fuel imbalance. Once fuel transfer isinitiated, excessive rudder trim may be required to stop and reverse the siphoning action of thefuel flow. Therefore, it is recommended that sideslip not be used to stop the transfer or change itsdirection while the intertank valve is open.

Misconception: The intertank valve opens and makes a simple connection between the left andright wing fuel hoppers.Fact: The intertank system consists of a motor-operated ball valve located on the rear beaminside the right wing hopper. A connecting duct is routed from this location forward towards thecenterline rib at BL 0 where the duct connects to the left wing. The left wing penetration islocated forward of the intertank valve (see attached figure). This geometry, combined withaircraft attitude and lateral acceleration, will influence the rate of fuel transfer from left to rightvs. right to left. Transfer of fuel from right to left will often require more lateral trim than a leftto-righttransfer.To successfully initiate fuel transfer in flight, the following procedure should be used:1) Using 2-3 units of rudder trim, initiate a sideslip in the direction desired.2) Open the intertank valve after the sideslip has been established.3) If additional sideslip is required, increase rudder trim. Up to approximately 5 units total maybe needed.4) Anticipate fuel quantity indication correction once the aircraft resumes coordinated flight. Donot continue to transfer due to the potential to over correct and transfer more than the requiredamount of fuel.5) Close intertank valve.6) Resume coordinated flight and note fuel quantity indications.

During ground operation, the intertank system performs in nearly the same manner as it does inflight. The direction of the fuel transfer will be towards the physically lower wing or towards ahopper that is not being maintained at overflow.During a recent wing hopper troubleshooting effort, an aircraft was leveled in accordance withAircraft Maintenance Manual (AMM) Chapter 8-01-00. A fuel quantity probe selector box andfuel quantity test box were installed to monitor the capacitance of the individual fuel quantityprobe(s) located in the left and right wing fuel hopper. The aircraft was fueled to 2,200 lbs. perside. Monitoring the hopper mounted fuel probe during fueling, both probes transitioned from adry capacitance value while the hopper was empty to maximum capacitance with boost pumpsrunning indicating that both hoppers were full. The intertank valve was opened, and a wing-towingfuel transfer of 150 lbs. during 15 minutes was recorded using the aircraft's fuel gages.The fuel load was balanced to 2,200 lbs. per side and the aircraft was leveled using the wing tipsas reference points rather than the AMM procedure. The intertank valve was opened, and thistime no measurable fuel transfer occurred over a 90-minute period. This verified that even aslight roll of the aircraft influenced intertank transfer.In summary, Gulfstream's investigation into operator reports of fuel transfer issues havedetermined that the VGs have no discernable effect on fuel transfer. Troubleshooting of theaircraft fuel system, wing hopper, and intertank system revealed no major discrepancies thatwould account for the reports. Gulfstream Flight Operations procedural guidance has resolvedthe concerns of several operators that reported issues.