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MINHAS866

prop pitch lock again and again

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MINHAS866

Hello to all

we have a problem with one of our c130 it's no 3 position engine prop gets pitch locked during decend again and again even we had changed three prop assembly on that engine so it's mean that problem is not with the props we had checked all engine related components and riging etc. but after three to 4 sorties problem comes again sir required ur feed back on this thanks 

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pjvr99

When you say "3 propeller assembly changed"  does that mean 3 different pump

and valve housing? If so, you will want to run your sync tester - sounds like a

synchrophaser or sync rack problem, or a wiring problem in main control

conduit. Bearing in mind PITCHLOCK can only occur with low fluid level or

overspeed conditions

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MINHAS866

Sir hi

I mean 3 propellers are changed we know that pich lock occurs 1. rpm over speed 103% 2. hydrualic fluid loss 3. Malfunctioning  of pitch lock assembly servo valve but there is no over speed indications hydraulic level are normal and as well as sychro phaser is concern mechanical gov has got no effect 

 

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pjvr99

Synchro operation can appear normal, but still cause trouble, which is

why I suggest running the sync tester. You mentioned that mechanical

governing has no effect - does that mean the crew put the prop to

mechanical before landing and it still pitch locked? 

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MINHAS866

No Sir how can we make a landing  with pitch lock prop when pitch locked governing fiction is over either it's normal or mechanical gov  I mean even prop set to mechanical before decend even then it pitch locked 

Can the malfunctioning nts system be a cause of this malfunction? Or any other thing in engine ?

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frank t

good evening sir, normally when you leave cruise altitude and start a descend to land and your prop is pitch locked rpm goes down and torque will start to climb if the blades are locked up. if you start your descend and rpm goes up it usually means you have developed a flat blade angle. your nts system is not bumping the prop. up. i'm assuming your in a 4 bladed e or h model in any event we would shoot the approach until either prop. or eng. limits have been exceeded then feather that engine and continue the approach if the prop. doesn't feather then their  other procedures to follow we would never try to land with a pitch locked, windmilling or uncontrollable prop. there are inflight pitch lock tests that can also gather info.  what we need sir is #####  TRQE, RPM ,F/F TIT, ALTITUDE  OAT, AND IF THE CREW HAS TIME ENG. GEN. FREQUENCY FOR THE AFFECTED ENG. THAT WILL VALIDATE RPM GAUGES . I hope this will help. good luck. p.s. my money is on prop. rigging or nts sys.  

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pjvr99

Please confirm that the following parts were NOT transfered from

one propeller to the next when the propellers were changed:

     valve housing

     pump housing

     PITCHLOCK regulator

     brass barrel nut

 

 

Thing that sticks in my mind is the PITCHLOCK system is essentially

mechanical, meaning once a COMPLETELY different propeller is

installed the problem should go away. I wonder if the problem being

experienced isn't maybe an engine roll-back .... this is just a thought

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frank t

good point pjvr. how about atmospheric vent to the fuel control ???

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MINHAS866

Sir whole prop were changed and i will post eng inst readings 

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NATOPS1
On 5/30/2017 at 1:54 AM, MINHAS866 said:

Sir whole prop were changed and i will post eng inst readings 

 

I mean 3 propellers are changed we know that pich lock occurs 1. rpm over speed 103% 2. hydrualic fluid loss 3. Malfunctioning  of pitch lock assembly servo valve but there is no over speed indications hydraulic level are normal and as well as sychro phaser is concern mechanical gov has got no effect 

Whole prop as in BOTH the Pitchlock regulator and PUMP housing were changed? 

Also please note pitchlock is not a result of the "hydraulic fluid loss" it is due to the loss of "PRESSURE" that holds the springs compressed on the pitch changing mechanism which is caused by a loss of fluid. The reason I say this is because if your pump is not making pressure then you will pitchlock without a loss of fluid.   

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MINHAS866
On 6/2/2017 at 0:44 AM, NATOPS1 said:

Whole prop as in BOTH the Pitchlock regulator and PUMP housing were changed? 

Also please note pitchlock is not a result of the "hydraulic fluid loss" it is due to the loss of "PRESSURE" that holds the springs compressed on the pitch changing mechanism which is caused by a loss of fluid. The reason I say this is because if your pump is not making pressure then you will pitchlock without a loss of fluid.   

Sir whole propeller assembly changed 3 times  including all the parts of propeller hope u understand now we know about the propeller my question  is does any thing in engine or rgb can cause or do with such pitch lock thing 

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pjvr99

There is nothing in the engine or RGB that can cause a pitchlock condition. However, I'm wondering whether crew is

giving correct debrief. You mentioned problem occurs during descent. If the NTS clearance is tight and pilots

throttle back too far too quickly, they may be engaging NTS system momentarily - query the crew on that.

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NATOPS1

As PJH said there are no "Engine" or RGB components that cause pitchlock.

There are certain parts that are reinstalled when changing a prop assembly (regulator, prop rings, prop nut etc) and the reason for my post.

Have you changed the Prop retaining nut? PJ called it the "brass barrel nut" if it is allowing pressure to bypass or leak you could get pitchlock. There have been many of theses dropped over the years.   

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MINHAS866

Sir Bundle of thanks to all for valueable feed back if the problem solved i will post it here 

 

 

 

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