need track replay Strange behavior of the ADI in flameout conditions.

[Silver_]

When for some reason (lack of fuel, engine failure, etc) the engine shuts off, and you are turning at a certain angle, the ADI stays working but out of calibration and does not mark the horizon correctly.

The solution I found was to go from MAIN POWER to BATT, the ADI automatically stops working (I don't know if this is normal too!!!) and level the plane with the SAI (this is always working, both in MAIN and in BATT) and , once the plane is leveled correctly, turn the switch to MAIN POWER again. With this I have the ADI, again, calibrated and working. Keep in mind that this flight was made in very low visibility conditions, hence the need to calibrate with the SAI.

My question is whether it is normal for the ADI to go out of calibration and lose its normal position due to an engine failure where the batteries are supposed to take the control. Also if when going to BAT it is normal for it to stop working.

Thanks

[BuzzLine]

1 hour ago, Silver_ said:

When for some reason (lack of fuel, engine failure, etc) the engine shuts off, and you are turning at a certain angle, the ADI stays working but out of calibration and does not mark the horizon correctly.

The source of attitude (EGI/INS) may have been degraded when the generators dropped offline and before the EPU kicked in.

1 hour ago, Silver_ said:

The solution I found was to go from MAIN POWER to BATT, the ADI automatically stops working (I don't know if this is normal too!!!)

It is normal, as the main ADI is powered by the Emergency AC bus that is tied to the EPU, not by the battery. EPU should start working as soon as the main and standby generators fail. It may take a couple of seconds to spin up and may have disrupted the power to your INS, causing the calibration issue.

1 hour ago, Silver_ said:

the SAI (this is always working, both in MAIN and in BATT)

The SAI is powered by the battery, so should work until battery power is depleted. When that happens, the unpowered gyros continue to provide usable attitude information for 9 minutes.

1 hour ago, Silver_ said:

once the plane is leveled correctly, turn the switch to MAIN POWER again. With this I have the ADI, again, calibrated and working

So your EPU has started and is feeding power to the emergency bus so the ADI is working again. I think your switch to battery/main caused the INS to start a realignment (ATT first) and that recovered the proper data to feed the ADI. I guess that switching off the INS, leveling the plane, then switching it back on (to IFA or just to ATT) would have brought the same result.

[Silver_]

2 hours ago, BuzzLine said:

So your EPU has started and is feeding power to the emergency bus so the ADI is working again. I think your switch to battery/main caused the INS to start a realignment (ATT first) and that recovered the proper data to feed the ADI. I guess that switching off the INS, leveling the plane, then switching it back on (to IFA or just to ATT) would have brought the same result.

In the firts points , thank you very much for the clarification. In the latter I disagree with you, since when you return to MAIN POWER and the plane is without the main engine running, it does not enter INS alignment, you can try this in a start-up and wait for the time you deem appropriate, it will never be aligned, DED doesn´t go too . I rather think that when resetting the electrical system the ADI automatically goes into autolevel mode. But I still have doubts that this is the case in the real aircraft.

Thanks my friend.

[BuzzLine]

Indeed, you are correct, I see the same things. I'm a bit confused by that "reset the ADI to level", it looks a bit fishy to me as I don't see any reference to this in the litterature. Also, the ATT alignment mode is not working as I'd expect it. Maybe someone with more knowledge can explain, I am out of my depth. However, the IFA alignment mode works : punch in the magnetic heading from the backup compass and in a few seconds, your attitude is correct and the position after a minute or so. That matches my understanding of the flight manual.

Some fun reading:  SNU84-1, the specs for the INU that was fitted in the F16 and other contemporary planes, https://apps.dtic.mil/sti/pdfs/ADB165119.pdf (unclassified)
It does mention that the unit should have its own battery to provide basic functionality in case the AC power is interrupted... Maybe that part of the spec was not followed, or our implementation is incorrect, who knows...

Cheers, buddy ! Fly safe.

 

[Silver_]

Thanks my friend you are right. Happy New Year, and thanks again.

[WHOGX5]

10 hours ago, BuzzLine said:

Indeed, you are correct, I see the same things. I'm a bit confused by that "reset the ADI to level", it looks a bit fishy to me as I don't see any reference to this in the litterature. Also, the ATT alignment mode is not working as I'd expect it. Maybe someone with more knowledge can explain, I am out of my depth. However, the IFA alignment mode works : punch in the magnetic heading from the backup compass and in a few seconds, your attitude is correct and the position after a minute or so. That matches my understanding of the flight manual.

Some fun reading:  SNU84-1, the specs for the INU that was fitted in the F16 and other contemporary planes, https://apps.dtic.mil/sti/pdfs/ADB165119.pdf (unclassified)
It does mention that the unit should have its own battery to provide basic functionality in case the AC power is interrupted... Maybe that part of the spec was not followed, or our implementation is incorrect, who knows...

Cheers, buddy ! Fly safe.

 

The EPU/emergency buses have always been broken in the DCS F-16, that's why you lose lots of systems that are supposed to still be functional during a flameout (like the INS). These issues have been reported years ago but they still haven't been fixed by ED yet.