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Can't pitchlock


HispanicMechanic
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Need a little more info..

Did your prop overspeed? To what RPM?

Also you may need to remove the dome and make sure you "rings" are indexed correctly. If they are off the pitchlock range "lobes" will be in the wrong position and prevent engagement of the teeth.

(I think you would have noticed them when you changed the regulator and the second one would have worked.)

But same person same day same issue it has happened before....

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see if the hub has put together correctly. if the slot for the dome key is not between 2 and 3 blades it will not pitchlock with a standard plr install. if it is overspeeding no problem, and you have already r2'd the plr once, and you are sure the index rings are correct....that should be your problem. you can advance the index rings to match accordingly if you are in a jam, but if the hubs are misaligned, i would have low confidence in the rest of the assembly.

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Doing a fuel governing pitchlock check. And can't get prop to pitchlock. changed out a regulator assy. but didn't work. Anyone got any ideas?

Seen this problem many times, with many causes. A lot of it has to do with how you are trying to pitchlock. I always have more luck moving my throttles to takeoff and then hit the switches after the RPM has stabilized. If RPM stays at 100% RPM with the switches engaged, think synchrophaser system failure, such as Synchrophaser, Valve Housing, or associated wiring (we had a plane come back from Depot with two wires crossed in the wing.) Also, check the C/B's. If the sync isn't getting power, it can't tell the speed bias motor to go to 106%

If RPM does increase when you hit the switches at takeoff, you may have the Fuel Governer set too low on the fuel control. You should do this check with an accutach if you are having problems. The limitations for the RPM setting are in the 1c-130h-2-61jg-10-1 s/s/sn 61-00-02 pg 1-84 through 1-86. You may also have a bad Pitchlock regulator from supply, seen that one before.

I suppose it is possible the TD Amp could cause this problem, so try the check in Null and see what happens.

I've never seen an improperly manufactured propeller cause this problem, but that doesn't mean it's not possible. Before you start tearing the prop apart looking for a smoking gun though, I'd look at the easy things. Definately actuate the fuel governor switches while already stabilized at power first and see if the electrical portion of the system is fully functional. If nothing happens, there's most likely nothing mechanically wrong with your prop.

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Your speed bias motor is fine.

When you placed the fuel gov switches to check your speed bias motor drove the prop gov to an "underspeed" and resulted in your overspeed...

Is this a "New" prop or was it already installed and failed during a post maint check?

As far as your indications... You had 104-105% RPM... What was your Fuel Flow?

I would assume your torque dropped off... Are you getting ANY torque difference or ZERO?

What TIT did you set prior to your check switch engagement? Did you try any higher settings?

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Your speed bias motor is fine.

When you placed the fuel gov switches to check your speed bias motor drove the prop gov to an "underspeed" and resulted in your overspeed...

As far as your indications... You had 104-105% RPM... What was your Fuel Flow?

As long as RPM didn't correct back to 100% on it's own, you're 100% right, but all he said was that RPM topped out at 104-105, he didn't say if it stayed there or not. 104 to 105% RPM can happen with Synchrophaser system failure if you perform the Pitchlock check correctly, with a throttle burst. That's why I prefer to perform the check while already at power.

HispanicMechanic, please don't leave us hanging like most people do with problems like this. Tell us what you find. Might help other people out down the line.

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The speed bias motor only does what you tell it to do. Check switches engaged overspeed, motor good. The pitchlock procedure requires the check switches to remain engaged so the RPM should never return to 100% during the steps.

Once you overspeed you advance the throttles to the firewall and record your FF and RPM then retard throttle until RPM is the same value (97% ?) as noted earlier... then check your torque looking for (2000 from the engine run book) 1000 (from the propeller book) increase from previous value (We use 2000 and worst case 1000)

Not sure I understand the process you use to check pitchlock...

We set TIT (book says to start at 925 then retry at higher TIT) (most of us start at 1000 or 1010) (why try twice)...

Then engage switches (look for overspeed) then advance to firewall for FF versues RPM numbers.

Do you engange the check switches then advance throttles (looking for overspeed)??? (throttle burst?)

I agree the prop is most likly built correctly, bad parts from supply...it happens.

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My apologies Natops, I guess I can be kind of unclear and rush through my explanations.

My intention was to show an easy way to check if the synchrophaser system is causing the problem. If you do the check correctly, you advance the symmetrical throttles above crossover, select locked, then retart the throttles until RPM drops 1% RPM from normal governing (AF), normally 99%. You note torque, then select the fuel governing check switches and advance the throttles to takeoff setting, then note RPM and Fuel Flow. While still holding the fuel governing check switches, retard the throttles until the RPM drops off to just where you hit the switches, normally 99%, then note torque again to verify pitchlock. You must have 500 in-lbs higher torque the second time (AF Prop and Engine Book).

What I was getting at was, if you hit the fuel governing check switches and advance the throttles, there is a problem with the synchrophaser system if the RPM returns back to 100% with the fuel governing check switches still selected, but we've had people, through lack of experience, think this malfunction is caused by a pitchlock regulator or fuel control, when in reality, they haven't even been able to do their jobs yet because the synchrophaser hasn't done it's job, due to wiring, power supply issues, or speed bias assy malfunction.

How I do the check? I personally like to bypass the first step and assume it's 5000 in-lbs (-7), go to 970 TIT (-7), then hit the fuel governing check switches to check for the RPM increase (if the sync system is malfunctioning, the RPM will remain at 100%), then decrease throttle setting until I hit 99%. I'm usually around 7,000+ in-lbs (-7). Doing it this way makes the check go by a little faster, and I'm usually not even close to 5k in-lbs, so I don't have to spend time staring at the torque gauge for accuracy. The less time spent in Pitchlock puts less stress on the first stage compressor vanes. I also have better luck successfully pitchlocking this way. I'm not really going against the book. This is the way our book tells us to do it if the first two attempts fail.

We've had ISO kick aircraft back to us for multiple props not pitchlocking the first time and expecting us to change pitchlock regulators for them. I'd do the check my way, sign the write-up off and kick it back to them.

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