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rpm flacuate


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Have you verified with your frequency meter? If not, do so.

From there try operating in Null see if it goes away.... If still there try going to Mechanical on the propeller control panel.

That should give you an idea if you should be looking into the FCU / TD system or at the Propeller / Propeller Valve.

Or pitch locking the propeller could help as well.


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rpm flacuate with normal TIT,FF and torque.how i solve this problem.

I've been taught only one way to troubleshoot this problem with engines running, and it usually isolates 90% of all fluxes to a specific system. It helps if, before you start, double check propeller servicing in case the low oil level transmitter (float switch) is failed and not showing a low oil condition.

1. Verify Freq's

2. Swap Indicators

3. Temp Datum Switches to null (If flux goes away, investigate TD system)

4. Mech/Gov switches to Mechanical (if flux goes away, check Synchrophasing system, including valve housing speed bias assy and throttle potentiometer)

5. Condition lever air start (if flux goes away, suspect dome seals, clogged standby filter, leaky low pitch stop/pitchlock regulator, or other internal propeller leakage)

6. Perform pitchlock check (if flux goes away, propeller is at fault, if flux stays, the fuel control or other wet fuel system component is most likely at fault).

If anybody else has ideas, let's here them. Please let us know what you find so we can add it to the pool of knowledge and pass it around.

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If the flux remains is it not only one thing...the fuel control?

Because of it's job and complexity, that's what I would change first, but if that doesn't fix it, it's plenty of other things that could cause this.

It also depends. If you have a very pronounced flux in everything, about 4000 in/lbs torque, and the bleed air pressure coming off the motor is going all over the place, that's a speed valve issue, but that's so obvious, you wouldn't exactly have to pitchlock the prop to isolate that one.

I suppose it's physically possible for some other fuel system component to cause this, but you are right, every time we've had a flux, slight or pronounced, after following all the steps and pitchlocking, it's been a fuel control issue.

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Try you simple things first.

1. Rpm indicator

2. Resync the prop.

3. Try a sync box.

4. Run the prop in mechanical. If flux is present in mechanical it's the valve housing because their is nothing else in the system to cause it to flux not even the TD system.

If you want to make sure it's none of the things that other people have said run the engine in null and bleed air off.


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  • 11 months later...

Sir!!....you have stable and normal TIT TORQUE AND FF!!...............check the freq meter. I bet you it is wondering too. Indication snag. Swap the gauges . Something to do with indication feed.!!!.............Tusker............ Work on it!!

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