View Full Version : Bell 407 RESTART FAULT question…
Weads
24th Oct 2022, 22:30
The Bell 407 RFM states that for a FADEC RESTART FAULT : When throttle is repositioned to idle stop (during engine shutdown) the PMA will go offline and engine may flameout. The PMA goes offline when the NP goes below 85% but the FADEC should still be supplied by DC battery/gen power. So my question is why would the engine flameout at idle with a RESTART FAULT? Thank you for any insight!
The Bell 407 RFM states that for a FADEC RESTART FAULT : When throttle is repositioned to idle stop (during engine shutdown) the PMA will go offline and engine may flameout. The PMA goes offline when the NP goes below 85% but the FADEC should still be supplied by DC battery/gen power. So my question is why would the engine flameout at idle with a RESTART FAULT? Thank you for any insight!
but the FADEC should still be supplied by DC battery/gen power
Which would be the issue. EEC is supplied with battery/gen power for start. There are diodes on this supply so that the battery/gen can supply power but not the other way around as the PMA should not be able to power the helicopter main bus.
When the throttle is at idle the FADEC would go to MANUAL with no power source and due to the follow up characteristic in the HMU it may go below minimum fuel flow to sustain the engine and it may flameout.
If you have no battery/gen power for EEC to start it then you have a FADEC RESTART FAULT.
Weads
25th Oct 2022, 13:04
Which would be the issue. EEC is supplied with battery/gen power for start. There are diodes on this supply so that the battery/gen can supply power but not the other way around as the PMA should not be able to power the helicopter main bus.
When the throttle is at idle the FADEC would go to MANUAL with no power source and due to the follow up characteristic in the HMU it may go below minimum fuel flow to sustain the engine and it may flameout.
If you have no battery/gen power for EEC to start it then you have a FADEC RESTART FAULT.
Thank you so much for that answer. I’m still trying to understand why the ECU wouldn’t have any power though? The book says that the ECU pulls from the higher voltage of either the PMA or battery/gen. If the PMA goes offline below 85% nP why wouldn’t the ECU automatically default to battery power? Also so I have this correct you said a RESTART FAULT would make the FADEC go into manual?
212man
25th Oct 2022, 15:26
Sure it's Np and not Ng? Just curious about rotors stopped scenarios.
Weads
25th Oct 2022, 15:33
Yes it is 85% nP
The Bell 407 RFM states that for a FADEC RESTART FAULT : When throttle is repositioned to idle stop (during engine shutdown) the PMA will go offline and engine may flameout. The PMA goes offline when the NP goes below 85% but the FADEC should still be supplied by DC battery/gen power. So my question is why would the engine flameout at idle with a RESTART FAULT? Thank you for any insight!
It's been a while, but I believe that while a loss of airframe power to the FADEC will trigger a FADEC FAULT light, it might also trigger a RESTART fault. A loss of airframe power would be the only situation where a loss of PMA power would cause an engine flameout.
Weads
25th Oct 2022, 17:20
That was my exact thought too LRP. Unless you killed the battery and gen under 85%np the FADEC should not lose power.
That was my exact thought too LRP. Unless you killed the battery and gen under 85%np the FADEC should not lose power.
You can lose airframe power with the batt/gen on, it's just a circuit going to the FADEC. It also would not be the first time BELL misplaced a "note" in a procedure.
helofixer
25th Oct 2022, 17:45
There is a fairly new procedure for an engine 150 hour inspection. It basically tests the PMA output with the ECU power killed. Hook up your computer, bring up Mterm, run the aircraft at 100% (warn pilot that he should go straight to cutoff, do not pass go if something gets sideways with the engine) pull the ECU Circuit breaker and using the Mterm program view the voltage from the PMA. At that point you are powering the engine solely on PMA power. After 45 seconds you will get a fault light, then you reset the circuit breaker, shut down normally and then clear your fault.
Weads
25th Oct 2022, 17:46
You can lose airframe power with the batt/gen on, it's just a circuit going to the FADEC. It also would not be the first time BELL misplaced a "note" in a procedure.
I do understand that you could lose power even with a battery and generator on but for it to lose that power there has to be a reason if a note is added into the RFM. I agree with you that it could be a misplaced note as well but I have heard this in my training and leads me to believe there might be something to it. So it could be one of those things that’s repeated and no one even knows why. I’m still trying to understand RVDT’s comment on the diodes though I lack the intelligence of you guys so it’s difficult for me.
There is a fairly new procedure for an engine 150 hour inspection. It basically tests the PMA output with the ECU power killed. Hook up your computer, bring up Mterm, run the aircraft at 100% (warn pilot that he should go straight to cutoff, do not pass go if something gets sideways with the engine) pull the ECU Circuit breaker and using the Mterm program view the voltage from the PMA. At that point you are powering the engine solely on PMA power. After 45 seconds you will get a fault light, then you reset the circuit breaker, shut down normally and then clear your fault.
I'm pretty sure you will get a FADEC FAULT light, the question is will you get a RESTART FAULT light also when you perform the test. If you do, it would explain why the "note" is included for the RESTART light.
Now before we go off on a tangent you only get 1 answer per day.
If you have a FADEC RESTART FAULT warning it can be helpful to now. Yes the DC system in the airframe may be fine but the power supply to the EEC for starting may be fritzed as there are a few small components which may have failed.
Bell is being polite and telling you that (A) you have a fault and (B) it may influence your decision on whether to shutdown the aircraft depending on where you might be at the time, and/or it may not shut down as expected
Bell is not alone in this scenario and it is fairly common on other types to do various tests to ensure the PMA and airframe circuit is operating as it should. PWC 200 Series for example.
I’m still trying to understand RVDT’s comment on the diodes though I lack the intelligence of you guys so it’s difficult for me.
Nearly everything electrical has an equivalent hydraulic analogy - diode = check valve. Will only let current flow in one direction and as mentioned you can't let the PMA power the main DC bus on the aircraft if you had a generator failure for example.
helofixer
25th Oct 2022, 18:04
Yes you will
"Remove airframe 28-volt power from ECU by pulling the FADEC circuit breaker in the
overhead panel, then dwell for a minimum of 30 seconds. A Restart Fault light should
illuminate in the cockpit."
Weads
25th Oct 2022, 18:09
Now before we go off on a tangent you only get 1 answer per day.
If you have a FADEC RESTART FAULT warning it can be helpful to now. Yes the DC system in the airframe may be fine but the power supply to the EEC for starting may be fritzed as there are a few small components which may have failed.
Bell is being polite and telling you that (A) you have a fault and (B) it may influence your decision on whether to shutdown the aircraft depending on where you might be at the time, and/or it may not shut down as expected
Bell is not alone in this scenario and it is fairly common on other types to do various tests to ensure the PMA and airframe circuit is operating as it should. PWC 200 Series for example.
Im with you in the power supply to the starting circuitry might be zapped but how would that make the engine flame out? As long as you have fuel the engine is technically self sustaining as it is already lit off.
Yes you will
"Remove airframe 28-volt power from ECU by pulling the FADEC circuit breaker in the
overhead panel, then dwell for a minimum of 30 seconds. A Restart Fault light should
illuminate in the cockpit."
That explains it. If a loss of airframe power triggers a RESTART FAULT light, then the 'Note" makes perfect sense. There are other faults that may trigger the light but the note would seem prudent if loss of airframe power is one of them.
Weads
25th Oct 2022, 18:23
That explains it. If a loss of airframe power triggers a RESTART FAULT light, then the 'Note" makes perfect sense. There are other faults that may trigger the light but the note would seem prudent if loss of airframe power is one of them.
If I’m understanding correctly your saying the RESTART FAULT “could be” triggered because of a loss of power to the FADEC therefor taking away the PMA it would have no power and the engine would flame out. Correct?
If I’m understanding correctly your saying the RESTART FAULT “could be” triggered because of a loss of power to the FADEC therefor taking away the PMA it would have no power and the engine would flame out. Correct?
That is correct. The FADEC C/W lights have multiple faults that will turn them on. If you look in the Manufacturers Data there is a matrix showing the various faults with associated lights. Helofixer verified the illumination of the Restart Light with a airframe power loss so the note makes sense, as it "could" indicate it.
Weads
25th Oct 2022, 18:45
Which would be the issue. EEC is supplied with battery/gen power for start. There are diodes on this supply so that the battery/gen can supply power but not the other way around as the PMA should not be able to power the helicopter main bus.
When the throttle is at idle the FADEC would go to MANUAL with no power source and due to the follow up characteristic in the HMU it may go below minimum fuel flow to sustain the engine and it may flameout.
If you have no battery/gen power for EEC to start it then you have a FADEC RESTART FAULT.
I guess one thing I’m still hung up on RVDT is that you say the FADEC is supplied with battery power for start. PMA takes over at 85% nP depending on voltage of it and the battery/ gen taking which ever is higher. So that makes me ask the question of what powers the FADEC when the aircraft is at idle and with an nP less than 85%
Weads
25th Oct 2022, 18:47
That is correct. The FADEC C/W lights have multiple faults that will turn them on. If you look in the Manufacturers Data there is a matrix showing the various faults with associated lights. Helofixer verified the illumination of the Restart Light with a airframe power loss so the note makes sense, as it "could" indicate it.
That makes perfect sense! Thank you guys for the plethora of knowledge you have shared with me! Thanks LRP for being able to put it in laymen terms for me!
helofixer
25th Oct 2022, 18:58
I guess one thing I’m still hung up on RVDT is that you say the FADEC is supplied with battery power for start. PMA takes over at 85% nP depending on voltage of it and the battery/ gen taking which ever is higher. So that makes me ask the question of what powers the FADEC when the aircraft is at idle and with an nP less than 85%
The FADEC ECU is supplied by the 28VDC Bus from 0% NP until 85%NP is reached. Then it chooses between the PMA and the 28 VDC bus, whichever is higher.
Weads
25th Oct 2022, 19:21
The FADEC ECU is supplied by the 28VDC Bus from 0% NP until 85%NP is reached. Then it chooses between the PMA and the 28 VDC bus, whichever is higher.
That’s what I thought. Thank you for the confirmation!