Fuel Filter ByPass

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Fuel Filter ByPass

Postby BoeingMn » 04 Oct 2020, 11:06

On the QRH of the 73NG addressing inflight fuel filter bypass, there are 2 conditions:
1 - one fuel filter bypass light illuminate
2 - Two fuel filter bypass light illuminate

in the first case it says "Erratic engine operation and flameout may occur on the affected engine due to fuel contamination." and flight continue

on the second it says the same "Erratic engine operation and flameout may occur on the affected engine due to fuel contamination. and Plan to land at the nearest suitable airport.

will fuel filter bypass causes engine flameout or it'll work normally?
flying single engine on a small twin non ETOP airliner is 60 minutes no matter what is your emergency, so why to continue with single bypass but land at the nearest with 2 bypass?

highly Appreciating your pro feedback
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Re: Fuel Filter ByPass

Postby sjap » 04 Oct 2020, 19:43

1 bypass may cause a flamout s thats not a big deal.
2 bypass may cause 2 flameouts, you will never know if and when. So the thoughts behind this is take no risk. Land asap before you get 2 flamouts.

It might not happen in real life, but on the other hand, i.ve seen this before due to fueltank contamination after heavy maintenance. They left some debris and old cleaning tools / towels inside the fuel tank. This caused clogged fuel filters. So it might happen. With two (impending) clogged filters you will not take the risk and fly further to your destination. You will never know when the filter is really clogged.

Fuel filter bypass light comes on when there is a delta P over the filter when it becomes clogged. It will not immidiately stop the engine. But since you do not know the amount of contamination, the filter may get clogged in a short period of time blocking all the fuel flow through the filter.

There is a bypass though, but then the engine gets unfilterd fuel. This may cause the fuel nozzles to become clogged as well. There is also a "last change filter"" installed in the fuel line. But again, if the contamination is too big, eventually everything will become blocked and the engine flames out. You will never know when that happens. So 2 lights on means "oh oh" and you'll have to land asap.
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Re: Fuel Filter ByPass

Postby BoeingMn » 06 Oct 2020, 15:39

Thanks a lot for your feedback
highly appreciated
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