fluctuating fuel flow indication C404
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fluctuating fuel flow indication C404
hey gents !
i freelance on a 404 and have experienced a fluactuating fuel flow indication in cruise and descend.
with engines leaned and set for cruise power after some time the right fuel flow starts to jump up and down , occasionally even up to redline fuel flow . then its ok again and restarts after a couple of minutes. i strongly believe it can be only an indication fault since the engine does not make any symptoms that the fuel flow really fluctuates that much - it runs smoothly regardless of the needle jumping .
on the other hand i have read there was an AD with the big bore continentals due to fuel pump seal failures where a fluctuating fuel flow was the first indication .
i talked with the maintanance about it and we looked at the mechanical fuel pump. its bone dry so there does not seem to be any leak. they cannot see anything and have no idea what the problem could be.
maybe i have luck and meet some technicians here who are familiar with maintanace and troubleshooting on this aircraft/engine and can give some hints what it could be so it can be sorted out.
engine is a continental GTSIO-520-M
thanks very much for any useful hints !
i freelance on a 404 and have experienced a fluactuating fuel flow indication in cruise and descend.
with engines leaned and set for cruise power after some time the right fuel flow starts to jump up and down , occasionally even up to redline fuel flow . then its ok again and restarts after a couple of minutes. i strongly believe it can be only an indication fault since the engine does not make any symptoms that the fuel flow really fluctuates that much - it runs smoothly regardless of the needle jumping .
on the other hand i have read there was an AD with the big bore continentals due to fuel pump seal failures where a fluctuating fuel flow was the first indication .
i talked with the maintanance about it and we looked at the mechanical fuel pump. its bone dry so there does not seem to be any leak. they cannot see anything and have no idea what the problem could be.
maybe i have luck and meet some technicians here who are familiar with maintanace and troubleshooting on this aircraft/engine and can give some hints what it could be so it can be sorted out.
engine is a continental GTSIO-520-M
thanks very much for any useful hints !
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What is the EGT gauge doing while the fuel flow is fluctuating? If it is doing nothing then it is probably the fuel flow gauge.
Further, what altitude are you at when it happens? The engines on both the C404 and 402 are prone to fuel flow problems at altitude - again the fix is to have the pumps on.
Lastly there was a modification for the pumps which required them to be on at all times to cure such fluctuations. Check whether your aircraft has been fitted with them. Incidentally, sometimes not even your engineers will know this so you need to check the flight manual for the amendment pages.
Before you flame me for this I was flying a C402 a few years ago and was idly leafing through the manual when I came across the relevant pages. When I mentioned it to the chief engineer he expressed some surprise at the fact. In his defence he hadn't carried out the modification.
Further, what altitude are you at when it happens? The engines on both the C404 and 402 are prone to fuel flow problems at altitude - again the fix is to have the pumps on.
Lastly there was a modification for the pumps which required them to be on at all times to cure such fluctuations. Check whether your aircraft has been fitted with them. Incidentally, sometimes not even your engineers will know this so you need to check the flight manual for the amendment pages.
Before you flame me for this I was flying a C402 a few years ago and was idly leafing through the manual when I came across the relevant pages. When I mentioned it to the chief engineer he expressed some surprise at the fact. In his defence he hadn't carried out the modification.
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thanks for the quick reply gents !
@ glum : i must say this might be a good idea to look closer for a gauge problem but was not performed so i don,t know.
@plovett : the egt gauge does nothing - i looked at it carefully during this. but the fluctuations are pretty quick - the fuel flow really jumps up to even redline and returns very quick, so not sure if the egt gauge would show up such quick changings.
nevertheless- i also believe its either a sensor , wiring or gauge problem because the engine does not show any roughness etc when this happens. i forgot to say the fuel flow always jumps to higher than normal- never saw an abnormal low flow indication.
we do with the 404 photosurvey and laserscanning missions and go depending on the mission up to FL230-250 . but first time i noticed it was a laserscanning at low altitude - 6000 feet.
both engines are brand new ( 80 hours) , delivered by ramaircraft , so i quess it has the improved mechanical fuel pump after seal failures were reported on a 404.
its also equipped with the improved two stage electrical auxiliary pumps as well new unfeathering accumulators , the manual on the c404 calls for aux pumps in low for take off, landing and vapor clearance and high for mechanical fuel pump failure.
when its only the wiring i do not care , my worry is about a slowly dying fuel pump which may suddenly flood and stall the engine- an engine failure with a heavy loaded C404 is everything else than fun.
cheers
@ glum : i must say this might be a good idea to look closer for a gauge problem but was not performed so i don,t know.
@plovett : the egt gauge does nothing - i looked at it carefully during this. but the fluctuations are pretty quick - the fuel flow really jumps up to even redline and returns very quick, so not sure if the egt gauge would show up such quick changings.
nevertheless- i also believe its either a sensor , wiring or gauge problem because the engine does not show any roughness etc when this happens. i forgot to say the fuel flow always jumps to higher than normal- never saw an abnormal low flow indication.
we do with the 404 photosurvey and laserscanning missions and go depending on the mission up to FL230-250 . but first time i noticed it was a laserscanning at low altitude - 6000 feet.
both engines are brand new ( 80 hours) , delivered by ramaircraft , so i quess it has the improved mechanical fuel pump after seal failures were reported on a 404.
its also equipped with the improved two stage electrical auxiliary pumps as well new unfeathering accumulators , the manual on the c404 calls for aux pumps in low for take off, landing and vapor clearance and high for mechanical fuel pump failure.
when its only the wiring i do not care , my worry is about a slowly dying fuel pump which may suddenly flood and stall the engine- an engine failure with a heavy loaded C404 is everything else than fun.
cheers
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Done the same work in a C404 as well as pax transport. Lovely machine. Sounds as though your aircraft is fitted with the same pumps as the ones I have flown.
Only suggestion I can make is to turn the pumps on low when next you see the fluctuations. If the fuel flow continues to fluctuate then it is the gauge - if it stabilises then where does it stabilise?
It should be a higher reading than before the pumps were turned on. You will have noticed that when turning the pumps off after take-off the fuel flow reduces, quite substantially. However, it does sound like a gauge or a sensor unit that is operating intermittently.
Only suggestion I can make is to turn the pumps on low when next you see the fluctuations. If the fuel flow continues to fluctuate then it is the gauge - if it stabilises then where does it stabilise?
It should be a higher reading than before the pumps were turned on. You will have noticed that when turning the pumps off after take-off the fuel flow reduces, quite substantially. However, it does sound like a gauge or a sensor unit that is operating intermittently.
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Only suggestion I can make is to turn the pumps on low when next you see the fluctuations. If the fuel flow continues to fluctuate then it is the gauge - if it stabilises then where does it stabilise?
you have experience on a C404 in photosurvey ?
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Dangerous butting on a tech log
Had a sudden intermittent change on the M.P.G. display on a fuel injected car engine. After A LOT of investigation,the fault turned out to be a very small leak on the pick up/inlet side of the fuel system. This was letting a very small amount of air in,which ' dashed' through the fuel flow meter,showing extra flow ,i.e. less miles per gallon. However,this small amount of air was,presumably absorbed into the fuel at the high pressure of the injection system,as the running of the engine was not affected. This was a t..t to find. Hopes this helps. (The leak was found to be a' scratch' on a copper washer in a connector.This was on 500 hp rally car engine!)
