Engine indicators wind down, Flight instruments OFF flags in view. All happened!

[Guest]

When the pilots did a normal banking, all engine indicators wind down, with all flight instruments OFF flag in view for 1 sec for a few times in flight. This sounds like an ESS Bus problem for my C130H.

However, i cannot find the fault and it happened again! Why did not the Generator Line Connector Switch seamlessly for this case? What could be the problems?

[tusker]

Good day!.... Interesting snag. I can imagine the faces of the crew members when everything look like a shut down!!........something to do with the instruments panel!!.......May be!!!...........................................John Boy

[pjvr99]

Sounds like a bus power problem. Look for a dry joint on a cannon plug pin, or

chafing in a 'P'-clamp ....... just spent 2 days chasing an RGB oil pressure flux

problem. Gauge would start flickering at about 850°C TIT and get worse as the

throttle was moved to T/O. Turned out to be one of the signal wires chafing

against the QEC frame, as the QEC twists in anti-torque.

Your problem sounds similar, increased 'G' in the turn, something flexing, who

knows. Hope you find it easily!!

[Lkuest]

When the pilots did a normal banking, all engine indicators wind down, with all flight instruments OFF flag in view for 1 sec for a few times in flight. This sounds like an ESS Bus problem for my C130H.

When you say all indicators, I'm assuming you are including RPM. Since the RPM indicators have thier own power source on the tach generator, this problem might actually be making the engines roll back, especially if the crew feels the plane slowing down or hears the engines quiet down when this happens. If the RPM indicators are rolling back, I suggest an immediate impoundment and a thorough check of the electrical system.

I have seen and heard of an A/C Instrument and Engine Fuel Control Inverter causing massive problems with engine performance, which might explain the indicators rolling back and the OFF flags. The Inverter also handles part of the Temp Datum system, which would explain an RPM rollback. There was a TCTO to identify and replace faulty relays that would allow the Inverter to affect the TD amps this way, but I don't know many details about it or if we actually replaced them. Maybe the next time this problem happens, have the crew immediately switch the invertor to a different position. The USAF aircrews were flying with the invertor in the A/C position for years, making this purely a bus problem, but now are flying them in the D/C position, which would mean a TR unit could be at fault as well as possibly the bus or the D/C side of the inverter.

If your RPM gauges are not rolling back, disregard.

[tusker]

Holy smoke!!!

[tenten]

Brother, xf14

1- “ALL†means “ALLâ€.

Are you sure that “ALL†the 32 indicators of the 4 engines (wind down) ??

(RPM, TORQUE, TIT, FUEL FLOW, OIL PRESURES,… etc). Or some of them.

And are you sure that “ALL†flight instrument (OFF flag in view)?

(ALTIMETERS, VVI, AIR SPEED INDICATORS,…etc). Or some of them.

2- (Wind down) does it mean, all the indicators dropped towards zero reading or….?

3- Is the defect appears only during the banking/turns?

4- Is there any other indications (such as blinking of any “Bus OFF†or GEN.OUT lights) during the malfunction?

5- Finally, is there any flight engineer on the seat ??! to deal with this according to flight manual sec.3…. (Switching OFF no. 2 generator to help in isolating the defect) since it is repeated/happened again and again.

More information will make things easy for others to help you.

[tinyclark]

I wish you guys would post tail numbers when you have a problem. There are so many different configurations, it makes it hard without knowing.

[SEFEGeorge]

The FE was out of the seat. The AC sent him to the back to see what it's like being a J-model AC. :p

[NATOPS1]

If the Generator is make voltage above 70 or 95 (depending on what system you have installed) you may not have any indication of a malfunction.

Low voltage on the ESS AC bus will cause all kinds of issues as long as the freqs stay above 368 or 380 the line contactor will remain energized and supply the ESS AC bus with BAD power.

The Voltage is too high for a Gen out light (and switching the load to a good generator) and not low enough to illuminate the bus off indicator.

The Inverter being ran all the time is a WHOLE OTHER discussion!!! (bunch of crap! Good idea totaly wrong reason.)

The Inverter being in the ON position will prevent some of the issues if it is an ESS AC bus issue. But you would have to have both inverters ON if you had engine instrument failures and ADI warning flags; this does point to an ESS AC bus issue as you stated.

You say the gages "roll off" including the RPM? As LKUEST stated if the RPM is moving you have a real problem (LOW ESS AC voltage affecting the syncrophaser) and not just indicators "rolling off".

The ESS AC has two sets of wires and CB's ESS AC (9 CB ) and upper main AC (9 CB ) check out your ESS AC Bus Isolation proceedure.

With that said I think you need to look at your Gen Output (maybe low) the Gen to Contactor wires (which are monitored by the ground fault transformers) which should take the generator off line (no excitation) and deenergize the line contactor (did not happen but may take a little time to trip).

The wires between the gen and the contactor are subjected to wing flex and I think this would be a good place to start. #2 Gen to the K2 relay.... Also the K2 relay may not release the contacts when deenergized ( too allow a good generator to assume the load).

[tusker]

I like so much the comment of SEFE George!!!!!!!!!!!............John Boy

[Guest]

It happened on my LAC 4840

Let me describe more in details

1) RPM, Torque, OFF Flags from ADI, HSI etc all happened for less than 1 second. i.e OFF flag came out halfway and became normal, Torque reduced by 1000lbs and returned to normal. The rest of indicators are not sure because it happened too fast.

2) No flickering of Generator Out Light occurs and it happened too fast to check for generator parameters.

3) No loss of engine power at all.

From the findings, it is a question of sudden loss of all essential power.

During troubleshooting, we managed to simulate the fault when we do a shake on the #2 Generator Control Panel (GCP). Opening up the bundle we found wire 23 broken. This wire is to provide the close circuit to GCP OUT light and nothing else. Funny thing is after repair of this wire and carrying out engine run, there is no more problems even though we shaked the wire. There are lots of technical questions on my mind!

a) Transition of the Generator Line Contactor (GLC) should be a seamless transitition. This can be confirm if you carry out an On Off of any generator switch. You should not have any loss of power and generator OUT light did not came on. Why?

Why AC Inverter could be a problem? I thought this does not affect your engine instruments?

c) I am suspecting the APU contactor (when the APU is in the air) temporary energised and disable the ESS Bus. Anyone shared the same view?

d) There is this suspicion that the GCP did not fit into the tray properly. However, a loss of GCP will most likely cause your FSR and GLC to come on and cause the OUT light to be on?

e) Will pulling the Isolated 28VDC to the GCP cause the generator to be down when all 4 engines are running?

Please advise and thanks!

NATOPS1

The Voltage is too high for a Gen out light (and switching the load to a good generator) and not low enough to illuminate the bus off indicator.

--- this is quite hard as the GCP will do a Overvoltage protection and trip the GLC relay in GCP.

[NATOPS1]

NATOPS1

The Voltage is too high for a Gen out light (and switching the load to a good generator) and not low enough to illuminate the bus off indicator.

--- this is quite hard as the GCP will do a Overvoltage protection and trip the GLC relay in GCP.

When I said "too high" I mean above the threshold of the GEN OUT light (say 97 or 80 VAC) not the Overvoltage protection...

There is NO under voltage protection (or indication) in the area between 115 V and 95 or 70VAC (depending on model), so if your voltage is between the level to illuminate the BUS (warning) and the level of the GEN OUT (protection) you will have an UNDERVOLTAGE condition on your bus...

A) The reason you do not get a GEN OUT light is because when you turn off the gen switch you de-energize the contactor to remove the GEN output from the bus so there is no route for power to illuminate the GEN OUT light.

The seamless switching actually takes some time (VERY VERY FAST though) because the contactor must de-energize, removing power then the contactor AUX contacts are made and the second GEN's power is routed to the BUS.

If the timing last too long you could see a bus off light but not a GEN out light because you turned it off (The GEN is still working just not used)

Start all engines and turn on all generators (not APU) then "downshift" your engines to low speed ground idle and you will be able to see the "switching" take place. (Blinking of lights etc)

The Inverter when ON supplies power to the AC INST and Engine Fuel Control Bus which powers you TQ, TIT and FF gages. Low voltage could cause inaccurate readings...

C) The ONLY way for the APU contactor to energize is if the APU gen is on speed (FSR) , developing good voltage (GCP), AND the GEN control switch placed in the ON position(route power to the contactor).

D) The GCP not in the rack is on of the MAIN causes for GEN issues. One of the first things we teach to do is reset the GCP in the rack....

E) Not sure, will have to look at the schematic... but, the ISOL DC is used for resetting the GEN in the case of loss of volts or the failure of the PMG in the GEN.

The internal workings of the GCP use 28VDC from its own internal TR unit so all the GCP relays are directly powered by the GEN output AC voltage, changed into DC and routed as needed.

Basically the AC is changed to DC and as long as it is good (above 95 or 70 VAC) it keeps the GLC and PIR energized to keep the Gen "online" and the GEN out light OFF.

So if all Engine GENs are ON they should remain ON if that CB is then pulled...

Try it and lets us know what happens.....

[tenten]

Now; no doubt to me that a “momentarily†loss of “Ess.AC Bus†is the cause of what you have seen.

Yes brother xf14; As you mentioned the normal shifting system of generators to take over the buses (generator contactors) during normal -no fault on them- should not cause the loss of bus to a point effecting the component/system working on it.(yes, in some cases you might see momentarily flickering of bus off light during shifting, but no more)

Based on the normal power rooting during flight:- No 2 gen-K53B-K53F-K53E- to the Ess. Ac bus.The following possibilities might be the cause of such defect:

A-Power source malfunction:-

1- No 2 gen. malfunction.

As mentioned by NATOPS1:

Quoting: If the Generator is make voltage above 70 or 95 (depending on what system you have installed) you may not have any indication of a malfunction.

And that is the critical condition in which the low generator output (voltage) cross the barrier of protection and warning indications, and the result is misbehaving not only with indicators but with systems (synchrophaser, autopilot , TD, etc) .

But this can be isolated by switching off no2 gen. by the FE (if not sent back by the AC) Which is the first action to be taken in the case of partial loss occur or suspected of Ess Ac Bus.(ref. dash1 sec.3)

Quoting: Service news vol.16 no4

A four-engine power fluctuation or rollback occurs when rpm and torque fluctuate in response to a failure in the aircraft electrical power system or synchrophaser system. Such a power fluctuation is usually a transient phenomenon lasting only a second or two, but the fact that the engines are responding to an uncommanded input can have an unsettling effect on the aircraft crew…..

B- Contactors control malfunction:-

1- Possibility of cycling of one of the gen. contactor (K53B) due to fault cycling signal imposed on it from GCP. (Internal malfunction of GCP, GCP tray holding mechanism not firmly in good contact, wiring loss on the tray receptacle of the GCP), the point of cycling might explain why not No1 generator takeover the Ess Bus and no warning light came in view within that short time of the fault.

2- The possibility of cycling the APU contactor K53E (K10) is there, but.. “Who Wag The Dog†??

Finally; I believe, that the defect as you mentioned related to looseness of the GCP and you will not see it again if GCP is in good contact with receptacle.

Quoting: xf14 Will pulling the Isolated 28VDC to the GCP cause the generator to be down when all 4 engines are running?

No, for my knowledge they are only for resetting the excitation field of the generators if lost.

Last point: No issue of AC inverter for my knowledge to this defect.

[tenten]

The FE was out of the seat. The AC sent him to the back to see what it's like being a J-model AC.

God save the crew, if that “AC†went a step farther towards F-22.:)

[NATOPS1]

During troubleshooting, we managed to simulate the fault when we do a shake on the #2 Generator Control Panel (GCP). Opening up the bundle we found wire 23 broken. This wire is to provide the close circuit to GCP OUT light and nothing else. Funny thing is after repair of this wire and carrying out engine run, there is no more problems even though we shaked the wire.

Wire #23 spilts off and runs to the contactor. Then back to the GCP...

[Guest]

Finally; I believe, that the defect as you mentioned related to looseness of the GCP and you will not see it again if GCP is in good contact with receptacle.

I am quite sure this could be the cause. But i can't explain why. I am assuming such situation is a case of GCP temporary switched off.

which means the GLC contactor should switch and the Gen Out light should be off. NATOPS1, there is a GLC contactor relay to activate the GEN OUT light on a separate route.

But such situation is like switch the generator on/off very fast.

1) There should be switching immediately and no loss of power?

2) GEN out light?

i am still very puzzled why loose GCP on tray can cause all the symptoms...

[NATOPS1]

When you turn off the gen you remove the route to illuminate the GEN out light....

Engine not running gen out light would be on no matter the position of the switch.

If you turn the switch ON with the engine shutdown you will get the GEN out light...

The GCP contains the control componets so if there are loose contacts the desired operation is lost. We teach "reseat" the GCP as a trouble shooting step.