Forum: F-16 Procedures

I've a question regarding trapped fuel.

Centreline and both internal wing were empty but aircraft is fitted with external wing tank with both showing 2400lbs each. But when external fuel transfer switch is put to WING FIRST, both wing tank started to transfer normally. What happened when putting to WING FIRST causing the fuel to transfer normally. Help needed. Thanks.

F-16.net Sponsor

Did this jet have 3 tanks? This part is confusing me. If the internals are below a certain level you can't xfer from the tanks. Please tell us again how the jet is configured.

Purple.

Jet is loaded with 3 tanks, centreline tank & both internal wing tank empty. But when putting to WING FIRST the both external wing tanks start to feed normally.

To me that is how they are to work........what is the issue?

The issue is the centreline and both external wing tank is to empty before the internal wing tank. With the external fuel transfer switch in NORM. Now centreline tank empty, both external wing tank did not feed and both internal wing tank empty. My question is why putting the switch to WING FIRST cause the external wing tank to start feeding.

Some valve not being shuttled or something. In NORM the ext tanks should've started upon centerline going empty. Dont know why it started taking from the internal wing unless maybe a bad float valve? Definitely time for a fuel shop consult cause something is screwy. Evil or Very Mad

Putting to WING FIRST causes the refuel/transfer valves in the wing tanks to de-energize. Thus, allowing the ext wing tanks to transfer the fuel.

Probably, the float switch in the vent tank is stuck at the high position.

This is definatly your centerline pylon bad, its tricking the jet into thinking the centerline is still full, by putting the ext transfer switch in wings first it overrides the pylon, change the pylon.

Visit your local support section and check out a fault isolation manual. Shocked

If your jet is equipped with three external tanks ,normally the centerline tank is used first . When the c/l is empty the wing external tanks start to feed into the wings. A Low level Float switch at the bottom of the c/l tank provides this signal. If this float switch fails , no fuel transfer from wing external to wing internal. Putting to WINGS FIRST overrides the normal transfer sequence and opens the wing external tanks.
I guess the float switch in the vent tank is not the problem because this one also shuts down transfer from the c/l tank ,leaving trapped fuel inside this tank. Change the c/l tank.

when the aircraft is loaded centerline and 2 external wing tank(drop tanks), pilot can select which external tanks feed first by selecting "EXTERNAL TRANSFER SWITCH ON THE PADESTRAIN PANEL" WING FIRST OR [Link pending approval] the "norm" position is selected,28vdc coming from ext fuel transfer curcit breaker goes to the ext fuel transfer ovverride relay in fuel matrix assy from here 28vdc goes to the centerline fuel tank low level float [Link pending approval] of centerline is full the float switch actuated and routes the 28vdc to both external wing tanks(drop) selenoid s of the refeuel transfer shutoff [Link pending approval] action prevent transfering fuel from external [Link pending approval] cl tank finishing transfering(empty),float switch in cl tank cuts 28vdc going to the external wing tanks and external wing tanks start [Link pending approval] yours is not [Link pending approval] reason can be your cl tank float switch is [Link pending approval] is emty but float switch stay up [Link pending approval] start external wing tanks transfer you must cut 28 vdc going to external wing tanks [Link pending approval] you selected external fuel transfer select switich to "wing first" ,28 vdc does not goes to the cl tank float switch and external fuel tanks selenoı[Link pending approval] hope this info helps [Link pending approval] advised that you study external tank transfer schematic diagram in -28fı-00-1 to understand system operation [Link pending approval] from TURKEY.

huagulong wrote:

Putting to WING FIRST causes the refuel/transfer valves in the wing tanks to de-energize. Thus, allowing the ext wing tanks to transfer the fuel.

Probably, the float switch in the vent tank is stuck at the high position.

If the float switch in the vent tank is stuck at the high point all external fuel tanks stop the fuel [Link pending approval] start the fuel transfer again in this fault,you should position "external tank transfer select switch" to "wing first"By doing this action you cuts 28vdc going to the float switch in the vent tank.

Forum: F-16 Procedures

Trapped fuel