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Which one should I go for...???


tenten
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Once upon a time; While initiating cruising speed at level 220 engine no.1 rpm started dropping to 97%, shifting to mechanical governing the rpm further dropped to 96%.

In flight pitchlock check procedure carried out as stated on section 3 of dash one, by moving the affected engine throttle “forward†while maintaining constant TAS, the result was no increase of RPM and no change of power (fuel,TIT, and torque) the pilot elect to shutdown the effected engine.

After three engine safe landing, the effected engine statically checked …… the only abnormality was “oil “ dripping from fuel control drain line!!!!!

In ground check during the start, the effected engine was coming to normal speed as a normal engine, but when moving the throttle from flight idle toward cross-over….. the fuel accompanied by TIT and torque started gradual abnormal increase while the RPM remain as it was (96%) the reading of the effected engine at just below cross-over was:

RPM 96%

TIT 1000⁰C

With 500 lb more fuel than other symmetrical engine.

The above reading was neither affected by shifting TD to NULL, nor shifting prop to mechanical.

Engine was shut-down to “recheck†throttle rigging… Rigging only checked..found “SATâ€.

On the second start and upon moving the throttle from flight idle toward cross-over the effected engine started behaving in a deferent manner….. RPM started gradual increasing and hit the 103% with extremely low fuel,TIT and torque.

Reading of the effected engine at just below cross-over was:

RPM 103%

TIT 720⁰C

Fuel flow 1100 lb

TP 4100 in/lb

The above reading was also neither affected by shifting TD to NULL, nor shifting prop to mechanical governing.

One more point… in both cases crossing the cross-over point had no any corrections..!!!

Guys of herkybirds; Is there any explanation to what’s going on.. :confused:..

And which one of the “three†should we go for….???

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Well, this one could be a tuffy.

It couldn't be the pitchlock regulator because it cannot cause high RPM, only low RPM with high torque. It could be a valve housing, as I have heard of them strangely causing high fuel flow problems. The fact that RPM is better in normal makes this more probable because the synchrophaser is capable of hiding valve housing problems, and it sounds like the synchrophaser knows something RPM related is wrong with the operation and trying to fix it. I don't believe it could be a fuel control, because the fuel control makes the engine put out torque, the prop's job is to use the torque by increasing blade angle, which slows the engine back down to 100%. In the flight range, the prop controls RPM almost single-handedly. If there are RPM problems, the Prop is the most likely culprit, no matter what the fuel control is doing. You may have two different problems, but I believe the Valve Housing is at least partly at fault. The easiest way to troubleshoot a problem with multiple likely culprits is to fix one problem at a time, the most obvious cause, and see what other problems are left. The valve housing might fix everything.

There is another possiblity, and that's the Coordinator. That component interprets throttle and condition lever inputs and translates them into a single throttle signal input into the valve housing. If something inside is messed up, the prop might think it's in the ground range, or maybe move it towards feather. It might explain everything, but it's a longshot. My vote goes to the Valve Housing.

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Not sure what oil from the FCU drain indicates as the fuel pump drain is also drained

on that line.

What you're indicating with the RPM is a valve housing governor failure. The prop

starts governing at 55 - 60° on the coordinator. Alternately, the synchrophaser is

also known to screw things up, even when master is not selected. Also a bad tach

generator, or prop pulse generator could be the culprit

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"Lkuest...

There is another possiblity, and that's the Coordinator. That component interprets throttle and condition lever inputs and translates them into a single throttle signal input into the valve housing. If something inside is messed up, the prop might think it's in the ground range, or maybe move it towards feather. It might explain everything, but it's a longshot."

Not such a long shot in my opinion. If the only thing done was to verify the rigging and you get two OPPOSITE results the input has changed. Your coordinator tells your blade angle where to be (in the ground range) and 1000C prior to crossover sounds like a rich fuel control.

Key to this is your "One more point… in both cases crossing the cross-over point had no any corrections..!!!" Did your correction light go out? I would think it would have or you would have added that information....

The overspeed condition i would not expect to see a correction (fuel topping) the first set of numbers 1000C prior to crossover i would expect to see a correction. If the coordinator is bad the system is never told where the throttle is so the fuel control prop and TD system alll have issues. Not so far fetched....

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"Not sure what oil from the FCU drain indicates as the fuel pump drain is also drained

on that line."

Is this draining near or at a garbox mount pad? In the the thrust engine world, oil coming from a drain line at the gearbox mounting points to a failure of the garlock seal. Not a tough fix if you have the puller.

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LKUEST, thanks for the information regarding that; Malfunction of a valve housing may cause high fuel flow problems.

If correct…., this might be one of the "missing chains" that will help in explaining most of the issue.

Thanks Pjvr99, the valve housing was confirmed at fault: regarding the other possibilities you mentioned (synchrophaser, bad tachometer generator, and the pulse generator) according to my understanding they are “out†upon shifting the prop to mechanical gov, which was done and failed to alleviate the defect.

NATOPS1, thanks for the input regarding the possibility of a defective Coordinator; But….to my understanding failure of this component can be either electrical failure (potentiometer) or mechanical failure; The electrical failure should be isolated by shifting the TD to null, which was done with no effect; While the mechanical failure should be detected during the static check of blade angles and throttle rigging, which was also not detected.

Quoting LKUEST:

You may have two different problems, but I believe the Valve Housing is at least partly at fault.

I agree 100% with what you are saying, and in fact it is approved that the defect is related to more than one component, and one of the most is the Valve Housing.

Quoting LKUEST:

The easiest way to troubleshoot a problem with multiple likely culprits is to fix one problem at a time, the most obvious cause, and see what other problems are left. The valve housing might fix everything.

Well, unfortunately –according to the first engine reading- we started the task with changing the FCU based on the assumption that; No component having the ability to misbehave with fuel -to the point of having 500 lb of fuel more than a normal engine- with TD NULL- accept the “FCUâ€.

The second point in pushing us to start with the FCU is the oil leakage (from drain mast) which was well beyond the static limit (and it was confirmed coming from FCU not the fuel pump (checked at the TEE joint of the two lines).

So as we changed the FCU and C/Out the RUN the defect remained as it was on the last…..high RPM (103%) with extremely low fuel, this defect remained constant during multi-starts and open power, therefore the next to "get down" was the Valve Housing….. Done…And the result was ….Engine power and RPM returned to normal..

Except…... The NULL start was low 730⁰C with no correction at x-over and the TD system failed to respond during temperature controlling check.

Therefore and after failure to increase the null start TIT from null orifice ….The third component (TD VALVE) was clearly asking to follow the others ……Done.……. All Defects Cleared.

Brothers, as you noticed we changed THREE components to clear the defect, two components out of the three I certainly having no doubt of their defectiveness (valve housing and TD valve) the one that I am not sure about it -regardless of oil leakage- is “The FCUâ€, if not at fault during high RPM (103%) and it’s only doing its over-speed protection by cutting fuel, what about the first reading low RPM (96%) with high fuel.

Or is it possible for a defective TD valve to act intermittently during open power only while TD in NULL and “Dump In†the bypassed fuel? ……. Hard to swallow.

Or is it as LKUEST mentioned; Malfunction of a valve housing may cause high fuel flow..???

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I wonder when these strange problems arise is one component is bad and is covered up by the corrections of a good component? Could they be cases of the pilots and FE thinking it's close enough until the problem can't be over looked?

Not long after the 95% torque BS got started by the AF I had a H model have low torque on one engine but still met the 95% torque I posted. I called "reject low torque" and we rejected and cleared the runway. The pilots thought it was good to go since we had the 95% torque on the one engine and 100% on the other three. I stuck to my guns and maint. replaced the valve housing and fuel control to fix it. The flight before the same day did not have the problem. I never posted 95% torque again unless it was a check ride. If it's not a certified 95% engine by maintenance it is not legal to fly it that way.

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