TRIP warning in HUD?

[Bog9y]

Hi guys,

 

Last night when I flew the Viper I got a message/warning on the HUD, bottom left, below NAV (I think) that said something like TRIP . I looked through all sorts of F16 manuals but couldn't find what it means.

 

I did get a BINGO warning prior to that and I did refuel air-to-air once. I can not remember exactly when the warning came but it would have been after the BINGO warning.

 

 

Does anybody know what this warning means?

[Bog9y]

Very interesting! Thanks for finding that! I didn't know that DCS had trapped fuel modelled. Looks like I'll need to do some more investigating on this

[Bouli306]

Very interesting! Thanks for finding that! I didn't know that DCS had trapped fuel modelled. Looks like I'll need to do some more investigating on this

 

Forgot to close the Air Refuel door maybe?

[Bog9y]

Nope, closed it after refueling. I can't remember if the warning appeared during refueling though.

[Bouli306]

Nope, closed it after refueling. I can't remember if the warning appeared during refueling though.

 

Did you see where the trapped fuel was located by using the fuel quantity select knob?

[Bog9y]

No, I was having fun with some friends in MP and didn't investigate further. I assumed it was some kind of bug with the avionics. Silly me

[SgtNickElis]

Hi, a bit late but here's the deal:

HUD TRP FUEL WARNING
A trapped external fuel condition is indicated by flashing TRP FUEL and FUEL in the HUD.

Five conditions must be met for a TRP FUEL warning to occur.
Conditions are:

• FUEL QTY SEL knob is in NORM.
• Aerial refueling has not occurred within previous 30-90 seconds.
• Fuselage fuel has been at least 500 pounds less than fuselage capacity for 30 seconds.
• Total fuel has been at least 500 pounds greater than fuselage fuel for 30 seconds.
• Fuel flow has been less than 18,000 pph for 30 seconds

Certain malfunctions can cause fuel to be trapped in the external tank(s).

The tank(s) in which fuel is trapped can be detected by a periodic check of external tank fuel quantities.
Accomplish steps 1 through 8 and 9 (if required) without delay:

1. Fuel flow - Minimize.
2. AIR REFUEL switch - Confirm in CLOSE.
3. AIR SOURCE  knob - Confirm in NORM or DUMP.
4. TEMP knob - MAN and adjust for comfort. This action usually increases ECS air pressure for external fuel transfer.
5. TANK INERTING switch - TANK INERTING to reduce internal tank pressurization.
6. EXT FUEL TRANS switch - WING FIRST.
   
   NOTE
   Selecting WING FIRST bypasses electrical components that, if malfunctioning, can prevent fuel transfer from external wing tanks, the centerline tank, or all three external tanks. With a three tank configuration, the first indication that the centerline tank is feeding is after the external wing tanks are emptied.
    
7. ENG FEED knob - NORM.
   A NVP TFR FAIL PFL and a fly-up can occur when NORM is reselected while operating in TFR.
8. Stick - Pulse aircraft in pitch several times by applying differential g forces of approximately -+2g.
   If the AIR REFUEL switch was initially found in CLOSE (step 2), perform step 9. If the AIR REFUEL switch was  initially found in OPEN (step  2), omit step 9.
9. AIR REFUEL switch - OPEN (1 second), then CLOSE.
   Open  or close AR door at or below 400 knots/0.85 mach.
10. External tank fuel quantity - Monitor.
    The time required to observe fuel transfer if the malfunction is corrected can vary from 13 minutes (for a full centerline tank) to 1012 minutes (for three external tanks with 500 pounds fuel in each) if reservoir tanks are full (i.e., both air ejectors are off).

    WARNING
    If a trapped external fuel condition is not discovered until either reservoir tank is less than full or a fuel low light is on, sufficient fuel transfer from the external tank(s) may not occur even if the malfunction is corrected. Consider fuselage fuel to be the only usable fuel.
    
    NOTE
    If trapped external fuel occurs after air refueling and completion of checklist steps did not correct the malfunction, consider descending well below the freezing level to unfreeze the external pressurization and vent valve. Cycling the AR door at lower altitude may restore normal operation.

11. Stores-Jettison (if required).

 
Ref.: Flight Manual T.O. GR1F-16CJ-1

I recently had one occur on my aircraft after aerial refueling but didn't know the procedure.

 

Edited January 18, 2022 by SgtNickElis

[MeanJim]

I've had this happen to me twice now.  Both times it happened, I had a center-line tank, but I've refueled with a center tank before without issues.  The first time it happened I was still practicing.  Both times I don't know if I disconnected and caused it, or if the trapped fuel caused the disconnect.  Both times I didn't notice the warning in the HUD right away because I'm not paying much attention to the HUD, I'm looking out and using visual cues to keep in place with the tanker.  I would get cleared to reconnect, and get in position but not get connected or take fuel.

The first time, I eventually noticed the warning in the HUD.  Since I was practicing, I paused and looked in the manual and didn't find anything.  I went back, and I don't know what fixed it, I was just flipping switches.  I flipped the tank inert switch, closed and re-opened the fuel door and some other things.  The error went away and I was able to continue filling up.  Last night however, even after getting the error cleared, I could not get more fuel.

I had been flying a while that night before this mission, so I was a little tired.  I didn't need to refuel to make it back, but decided to do it to get in the practice since it had been a while.  I had the bingo page up on the DED so I didn't have to look down at the fuel gauge.  Just as I was cleared contact with the tanker, the bingo fuel warning went off.  I hooked up and got to just over 6000lbs when I disconnected when the tanker started its turn and I got too slow.  I was able to re-connected, but not long after that I got disconnected again when the tanker leveled off.  It didn't feel as if it was my fault, I thought I was still in position, but I'm not 100% sure.  I was unable to get reconnected though.  I was in position, but not hooking up.  I then looked and saw the error in the HUD, so I aborted the refueling, backed off and tried troubleshooting it.

I'm pretty sure the fuel gauge was showing over 8000lbs total.  I turned the QTY switch to center and it was showing 1000lbs. in the center tank.  I closed the fuel door, flipped the tank inert switch, and now the gauge was showing the center tank empty.  The error went away, so I re-opened the fuel door and tried topping off.  The tanker just would not hook up though.  I was cleared, the lights were on, the boom was moving, but I could not get fuel.  I eventually gave up and landed.