Fuel system behavior and other issues
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Hello. I ran into suspicious behavior of the fuel system on BAe 146 and would like to know if it works as intended.
A long story
I have been flying with random failures enabled recently and got a right outer fuel pump failure in cruise. I shut the pump down and took no other action thinking the R standby pump would step in. It was only later I found that standby pumps do not supply fuel to the engines. IIUC the correct response would be to open the R common feed valve so that R inner pump feeds both engines 3 and 4.
Anyways, with the R outer pump both broken and off engine 4 soon starved and flamed out, which is understandable. I have landed succeffully on three engines and decided to handle this situation again in a practice flight. This is where things got a bit weird.
For the first test I have triggered the R outer pump failure manually in the EFB. FUEL and R OUTER LO PRESS annunciators have immediately turned on. Without waiting for the engine to shut down I have switched the pump off and opened the R common feed valve. The engine kept running normally as expected.
Then I decided to repeat the failure but let the engine flame out and restart it in flight:
- R OUTER PUMP FAILURE (EFB): OFF
- R OUTER PUMP: ON
- R COMMON FEED: SHUT
- R OUTER PUMP FAILURE (EFB): ON
Then I waited for the engine 4 to stop but, unlike the original flight, this has never happened. Switching the R outer pump off also did not interrupt the fuel flow.
As an experiment I have turned ALL engine pumps off and waited for a couple minutes but the engines just kept running normally at the same thrust setting (~80% N1).
I then triggered failures of ALL fuel pumps including the standby ones in the EFB. No effect, the engines kept running normally.
I have restarted the flight several times and tried both switching the pumps off and triggering fuel pump failures in different combinations. Switches never seems to affect anything. Triggering the failures, on the other hand, sometimes stops the fuel flow to the respective engine, about 1 time out of 10. In other cases only the annunciators are lit.
TL;DR
I found that turning some or all engine pumps off does not stop the fuel flow to the engines. This happens regardless of X FEED and COMMON FEED valve states. Is this as designed? I may still be missing something obvious about the fuel system.
I also found that triggering pump failures in the EFB rarely makes the pumps actually fail. In most cases only respective annunciators are lit but the fuel keeps flowing. Is this as designed? Could there be different kinds of the same failure (real ones and false positives)?
Other issues
While experimenting with this I also noticed other, more serious issues. I am not sure if all of them are known:
- Loading a saved BAe 146 flight crashes MSFS 100% of the time. This used to work in earlier versions and still works with other aircrafts.
- EFB occasionally hangs and becomes completely unresponsive. Hiding it and showing again has no effect.
- Shape of the holding pattern perfomed by the autopilot in LNAV mode is far from the expected oval. It resembles an open envelope instead. This is already reported on the forum.
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I don't have an 146 FCOM but have one for the RJ. In there it says:
"If an engine is not supplied by an electrically driven pump, the engine will keep running under gravity feed." Which makes sense due to the physical positioning of tank and engine.
Turning off pumps and the feed valves does not close the low pressure valve to the engine. Those can only be closed by pulling the fire handle.Now why the engine died in one situation and not the other I am not certain and would have to dive deeper. Perhaps it depends on fuel level and power-settings (maybe even any manoeuvring you were doing?). Perhaps pump failure has a random chance that mechanical parts of the pump broke and are blocking the lines?
I imagine that in some situations gravity feed would not be able to provide a sufficient rate of fuel to keep the engine from flaming out. -
This is something that came to light in a community stream around the time of the 146 V2 release when one of the streamers accidently switched off one of the fuel pumps in flight. Up until that point, I don't think anyone has ever tried turning a fuel pump off in flight! And now, just like buses... 😉
The logic in the real 146 is that if a fuel pump is switched off, the standby pumps will continue to supply fuel to the engines. There is one standby pump in each wing supplying the inner feed tanks, and they are powered by the yellow hydraulic system.
If the standby pumps fail, then gravity will keep the feedtanks full until approx 2,000KG of fuel remains per side.
This isn't how its currently working in our simulation of the 146 but we do have this noted as an area to improve in the next update. The reason you are likely seeing differences in the engine shutdown logic is due to speed and altitude. At high altitudes, the engines are more reliant of fuel flow, so if one of the fuel pumps is switched off at high altitude it will likely lead to an engine shutdown. At lower altitudes, switching off the fuel pump will likely not effect the engine.
Mark - Just Flight
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Thank you for the explanations!
I did expect some gravity flow: after all, APU starts and runs fine on the ground even with L inner pump off. I just never expected it to be enough for engines on cruise thrust.
All test flights were at FL170 so I am still a bit puzzled by the inconsistency in failures. But it could indeed be that shutdowns were related to holding pattern turns or less fuel remaining. All in all I do not think this is too important.
Does it make sense to report the load flight and the EFB freeze issues elsewhere or are they known to the dev team?
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@grue There are a couple of reasons that I can think of that would cause the EFB to be unresponsive:
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If the EFB displays a "license failure" message this would point towards an activation/installation issue. If this is the case we would recommend getting in touch with our support team via the following link and they will be able to help troubleshoot that with you: https://www.justflight.com/support
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A recent update to the Horizon Sim 787-9 mod caused a compatibility issue with the EFB/tablet in our aircraft. Horizon Sim has since released a further update fixing this compatibility issue, so if you are using this mod, we would recommend making sure that it is fully up to date.
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Simconnect become a bit unstable after multiple flights and can prevent the aircraft's gauges to correctly load (usually evident by a "loading aircraft" message on the EFB). If this occurs, try pressing the pause/break key on your keyboard a couple of times to see if that 'kicks' the aircraft back into life. If not, the only other solution we could provide is to restart the simulator.
With regards to the other points you have raised in your original post, we currently have a fix in testing for improved holding patterns with the UNS-1 and this will be included in the next update. The crashing when loading a saved flight isn't something I have seen reported before, and I personally haven't tried to load a saved flight, but we'll get that logged so we can try and replicate that on our end. If we can replicate it, we will investigate it further and include a fix in a future update to the 146.
Mark - Just Flight
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@grue without wanting to talk down this otherwise great product: but I do not think turn bank or fuel remaining is factured in. It's like I said once: not a lot of people will try these features but when you do, there's not a lot of addon planes that hold up to the promises made ih those mouth watering trailers. Not even the ones of his lord almighty RR. (Leonardo being the only real exception to that, as far as I can judge)
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@Mark , I do not have the 787 installed neither did EFB did not display any messages when frozen, it just got stuck at the aircraft config page and did not accept any input. The aircraft was otherwise controllable. I will see if I can reproduce this.
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If the outer low pressure illuminates due to a pump failure, the recovery is:
- left and right STBY pumps ON
- relevant common feed OPEN
That should restore operation.
