Forum: F-16 Procedures

To question this a bit furthur in a different direction... As an F-16 Fuel Systems instructor, the question about tank inerting came up. I know what the T.O. says about it, I know what the wiring diagrams say about it, but I need a pilots point of view.

Do the External Tanks continue to transfer when the tank inerting switch is placed to tank inerting? T.O.'s tell me they should continue as the TI switch should have no effect. The jets we work on have the Halon system disabled due to the harmful nature to the environment as stated above, so I can't verify it directly.

A co-worker tells me he did a test on an enabled jet during a deployment and the externals stopped transferring, but due to the statements in the T.O. I would like some additional accounts of this.

Any information anyone could provide will make my classes better! Thanks!

DWSKAMS

F-16.net Sponsor

When the tank inerting switch is turned on it uses halon to pressurize the internal fuel system but drops the pressures to combat mode(internal only). The external tanks remain pressurized with ECS air. If you notice when a pilot comes back from a mission with trapped external fuel the tank inerting switch is on. This is to try to help fuel transfer by lowering internal pressure.

If the Externals stay pressurized, why don't they transfer, causing a trapped fuel condition? Lower Internal pressure shouldn't affect External transfer. The Internal tanks drop to combat pressure (does the injecting of Halon into the tanks cause the pressure to go up at all?), but they are still transferring by the siphon method, as well as powered transfer. It seems that the Externals should still transfer.

Thanks for the info!

The Halon bottle is used primarily when the jets are in a combat zone. Due to the Ozone depleting properties of the halon stateside and home bases overseas usually have the fuel inert C/B pulled and collared and the bottle itself purged with nitrogen. Hope this helps.

DWSKAMS wrote:

If the Externals stay pressurized, why don't they transfer, causing a trapped fuel condition? Lower Internal pressure shouldn't affect External transfer. The Internal tanks drop to combat pressure (does the injecting of Halon into the tanks cause the pressure to go up at all?), but they are still transferring by the siphon method, as well as powered transfer. It seems that the Externals should still transfer.

The tanks are gravity fed, and they use 17-19 psi to transfer the fuel back into the jet. IF the fuel system pressure drops due to the tank inerting system being activated, this would affect the fuel transfering out of the tanks.

I feel like I should clarify on the F-15 fuel system. Commanded dump will only come out of the right wing because the dump valve routes fuel to the right wing surge box only. Uncommanded dump can come out the left, right, or both wings. It all depends on where the originating point of the fuel entering the vent system is coming from. The internal fuel system is pressurized at a range of .2 to .8 psi when the aircraft is in the air. Primary pressurization is obtained via a fuel pressurization shut off valve that is opened once in the air. Should this fail, there are two back-up ram air pressurization valves that are utilized, which scoop forced air in from inside the left intake area. If the aircraft has a static fuel venting problem and the surge boxes are full, there is a possibility of fuel coming out of the wing vents during flight, but not more than a few gallons--the surge boxes only hold 4 - 5 gallons each.

The F-16 Halon is not used during training. Meaning the bottle is empty and the circuit breaker is usually collared open. When operational and TANK INERT is selected, external tanks lose all their pressure and internals go to 1-3 psi. Halon is then mixed into the ECS inlet source just before the internal V&P inlet. This system is vital to the F-16 because there is no fire supression foam inside the fuel tanks, which the F-15 has. No foam, equals a ton of weight savings, as I am sure this was the reason why halon was selected over foam.
The latest fire supression system is in the F-22, which uses nitrogen as the gas of choice. But thats a whole different story!

IDCrewDawg wrote:

DWSKAMS wrote:

If the Externals stay pressurized, why don't they transfer, causing a trapped fuel condition? Lower Internal pressure shouldn't affect External transfer. The Internal tanks drop to combat pressure (does the injecting of Halon into the tanks cause the pressure to go up at all?), but they are still transferring by the siphon method, as well as powered transfer. It seems that the Externals should still transfer.

The tanks are gravity fed, and they use 17-19 psi to transfer the fuel back into the jet. IF the fuel system pressure drops due to the tank inerting system being activated, this would affect the fuel transfering out of the tanks.

I'm thinking the system was designed to keep in mind that if TANK INERT was selected, the externals would most likely be jettisoned prior to combat. That being said, any remaining fuel would be lost. If indeed there was fuel left in the external tanks, the pilot would get a trapped fuel advisory in the HUD, as this condition meets all the five requirements for TRP FUEL to display in the HUD:
1) Quantity select in NORM
2) Air refuel in CLOSE
3) Fuselage fuel below full (I cant remember the exact amount...maybe 250 pounds?)
4) Internal wings and external tanks total quantity exceed 250 pounds (again the number is off my head)
5) Fuel flow is below 10,000 lbs per hour. (Another guess on the number)

Also, all of these conditions must be met for more than 30 seconds. (Sorry for all the guessing. I dont have access to TO's right now)

In any event, DWSKAMS is correct in saying that the external tanks do not pressurize when TANK INERT is selected. This is because the valve is de-energized to not accept any pressure. (just like when pressurizing the system on the ground without power...the externals should not pressurize.)

Forum: F-16 Procedures

Halon inerting system/Vortices