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engine downshifting fire


sharif101
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on dash 7b engine #3 engine propeller brake locked then we try to unlock but failed.we gave apprx 10 us gal hot oil inside the RGB for prop brake release but failed to release.then RGB change & engine fitted.during Ground run found oil flashing from bleed valve ,drain mast also white smoke from tailpipe.we attempt 2nd start found no white smoke but during power reduce from takeoff to below x-over at that time flame out with poping sound after 2-3 second interval it happen several time at that time i shutdown engine manually.during flame out fuel flow increase suddenly.other parameters normal.TD sys calibrate & TD valve changed again ground run but problem remain

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When you retard the throttle, does the RPM drop with the throttle? If so, this situation possibly indicates a pitchlocked propeller and requires an investigation. Someone possibly forgot to install, or damaged the pitchlock regulator seals when the propeller got swapped over to the new RGB.

Also consider Foreign Object damage to the compressor. Check 5th and 10th compressor blades.

Borescope turbine for damage?

NTS Gap too small when pulling the pump housing towards you?

What is the engine efficiency?

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I suspect the engine 'popping' noise is a result of flooding of the compressor

during the initial attempt to release the prop brake. If the forward drain plug

was not removed from the RGB, the oil would be forced down the T/M shaft

into the power section. This would account for oil from the bleed valves and

drain mast, and masses of smoke from the tail pipe.

As the bleed valve system gets air from the diffuser, we may assume that

some of the oil in the compressor got into the speed valve, and is sticking

part-open or made sensitive to throttle-back movement, and bleed valves

are popping open

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all throttle position FF,TIT,RPM,TRQ normal but only throttle back to just below Xover then flame out & sound produced 2-3 second interval but when TD null then no flame out.TD ams test check 2 times found good,cordinator check ok,thermocuple,harness,5th & 10th stage bleed valve,turbine check found good.now what can i do?pls anybody help

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Dash 7 or 101 make the task difficult to analyse, but as you mentioned on the last post with TD null the engine is behaving good, if so then your target is the TD system only.

But if in NULL and below x-over some engine parameters are abnormal then the target is more than TD only; it can be acceleration bleed air valves issue as PJ already mentioned.

Sticky valves resisting to be fully close at low power causing the engine to bug down especially with TD in operation.

("popping sound" is a clear indication of the cycling of the bleed acceleration valves.)

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You say it works in Null so maybe a rich lean check on your fuel control. (NO correction at crossover in NULL)

Popping noise may be the engine trying to maint ignition but the air fuel ratio is not good.

What is the "correction" to the TIT at crossover?

A large increase as you enter temp controlling above crossover means a large decrease in TIT as you move below crossover.

Check the filter between the 14th stage and the SSV. If oil is/was in the compressor it may have clogged the filter just enough to reduce the air flow to the SSV.

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all throttle position FF,TIT,RPM,TRQ normal but only throttle back to just below Xover then flame out & sound produced 2-3 second interval but when TD null then no flame out.TD ams test check 2 times found good,cordinator check ok,thermocuple,harness,5th & 10th stage bleed valve,turbine check found good.now what can i do?pls anybody help

When you checked the coordinator, did you check both the 65 and 66 degree switches for breaking contact above 65/66 as well as getting contact back above 65/66? I would also slave a Relay Box in and see what happens. I'm thinking it's possible that the TD system stays in Temp Controlling mode even below the useful range of the coordinator potentiometer, causing the amp to go to full take. The popping could then be caused by the engine dropping below 94%.

Don't forget the "Flag" check. Upspeed the engine, then put a rag secured to a seat rod up in the left and right bleed collectors and see if the rag whips around, indicating an open bleed air valve.

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As a side-note, I have a direct-reading gauge hooked up to the bleed valves during all

runs on the cell. I had an engine surging intermittently, mostly during throttle back,

but all throttle settings, and sometimes even at stabilized throttle setting. Eventually,

during man-on-stand, I heard a puffing sound, and put my hand in front of the speed

valve. Installing the gauge showed a momentary drop of up to 30psi, thereby opening

the bleed valves.

Since then I have found that a difference of more than 10 -15psi between CDP and

speed valve pressure is enough to momentarily pop the 10the stage valves during

some throttle movements

Lquest has asked a good question on the rich/lean, and the cross-over correction

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yes, i checked coordinator both 65&66 degree switch.relay box replace new one.now problem shifted today given ground run 2 times.TD null 3times check but 1 time flame out.last time when TD auto and throtle back to flight idle TIT 720 degree then flame out with sound at that time FF increase 500pph,TIT above 900 degree & RPM 93%.i think bleed valve open since RPM below 93%.is it FCU problem?ssv filter check ok.pitch lock regulator replace new one.Xover TIT 775 degree.

can i change acceleration bleed valve?

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I understand from the last last post that even in null the engine is flamed out; and that the RPM dropping to 93% just before the flame out.

To me once the RPM dropped to 93% and bleed valves opened it is normal to see what you have seen.

Based on that, I see no benefit of changing the acceleration bleed air valves.

It seems to me that the main issue is RPM dropping once power retarded; then the puzzle need to be answered;

Way at flight idle the RPM dropping below the threshold of keeping the acceleration bleed air valves closed (94%)?

Is it a fuel Issue (FCU lean) (blocked fuel nozzles) or a valve housing issue, or the low pitch stop setting is high accompanied with less fuel?

And I believe that the answer can be obtained from your engine instrument if you read and compare them with the symmetrical carefully.

One thought: Use the credit of the null orifice and let more fuel to go and see what will happen while engine bleed air valve in closed position.

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What is the engine efficiency?

When the speed drops, what is Torque?

During flameout, check bleed air manifold pressure of that one engine.

Have you checked the engine for bleed air leaks using a man-on-the-stand runs?

How is the gap in the propeller torque retainer lug assembly? NTS bracket?

Have you inspected the compressor 5th and 10th for damage?

Have you inspected the turbine module for damage?

Check Low Speed Ground Idle anti-ice check for 24 degree rise with bleed closed.

Check what the blade angle is at Flight Idle and Low Pitch Stop

You can also disconnect the Compressor Inlet Pressure line from the Air Inlet Housing and blow 80-120psi of air pressure into the Air Inlet Housing side of the disconnected line.

You can change acceleration bleed valves, but to check them, disconnect the line coming out of the Speed Sensitive valve and apply a low amount of air pressure, then check to see if all the valves closed. It is easiest to check the 12 and 6 o'clock valves with a borescope through the bleed collectors. After you apply low air pressure, apply a vaccum and see if the valves open again. If they do this easily, the valves are all good. If one is not as free, it is probably dirty or frozen.

It is possible you have a bad fuel control, but I don't see how a fuel control can cause low RPM and high fuel flow at the same time. It sounds a lot to me like a bad air system or NTS. These would cause a rich "Bog Down" you are experiencing. It seems pjvr99 has good experience that isn't in any book I've read, and everything he says makes sense. Good luck!

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This should be all of the thread,

#1 sharif101

engine downshifting fire on dash 7b engine #3 engine propeller brake locked then we try to unlock but failed.we gave apprx 10 us gal hot oil inside the RGB for prop brake release but failed to release.then RGB change & engine fitted.during Ground run found oil flashing from bleed valve ,drain mast also white smoke from tailpipe.we attempt 2nd start found no white smoke but during power reduce from takeoff to below x-over at that time flame out with poping sound after 2-3 second interval it happen several time at that time i shutdown engine manually.during flame out fuel flow increase suddenly.other parameters normal.TD sys calibrate & TD valve changed again ground run but problem remain

_____________________________________________________________________________________

Lkuest

When you retard the throttle, does the RPM drop with the throttle? If so, this situation possibly indicates a pitchlocked propeller and requires an investigation. Someone possibly forgot to install, or damaged the pitchlock regulator seals when the propeller got swapped over to the new RGB.

Also consider Foreign Object damage to the compressor. Check 5th and 10th compressor blades.

Borescope turbine for damage?

NTS Gap too small when pulling the pump housing towards you?

What is the engine efficiency?

_____________________________________________________________________________________

pjvr99

I suspect the engine 'popping' noise is a result of flooding of the compressor during the initial attempt to release the prop brake. If the forward drain plug was not removed from the RGB, the oil would be forced down the T/M shaft into the power section. This would account for oil from the bleed valves and

drain mast, and masses of smoke from the tail pipe.

As the bleed valve system gets air from the diffuser, we may assume that some of the oil in the compressor got into the speed valve, and is sticking part-open or made sensitive to throttle-back movement, and bleed valves are popping open.

_____________________________________________________________________________________

#1 sharif101

all throttle position FF,TIT,RPM,TRQ normal but only throttle back to just below Xover then flame out & sound produced 2-3 second interval but when TD null then no flame out.TD ams test check 2 times found good,cordinator check ok,thermocuple,harness,5th & 10th stage bleed valve,turbine check found good.now what can i do?pls anybody help

_____________________________________________________________________________________

tenten

Dash 7 or 101 make the task difficult to analyse, but as you mentioned on the last post with TD null the engine is behaving good, if so then your target is the TD system only.

But if in NULL and below x-over some engine parameters are abnormal then the target is more than TD only; it can be acceleration bleed air valves issue as PJ already mentioned.

Sticky valves resisting to be fully close at low power causing the engine to bug down especially with TD in operation.

("popping sound" is a clear indication of the cycling of the bleed acceleration valves.)

--------------------------------------------------------------------------------

NATOPS1

You say it works in Null so maybe a rich lean check on your fuel control. (NO correction at crossover in NULL)

Popping noise may be the engine trying to maint ignition but the air fuel ratio is not good.

What is the "correction" to the TIT at crossover?

A large increase as you enter temp controlling above crossover means a large decrease in TIT as you move below crossover.

Check the filter between the 14th stage and the SSV. If oil is/was in the compressor it may have clogged the filter just enough to reduce the air flow to the SSV.

--------------------------------------------------------------------------------

Lkuest

When you checked the coordinator, did you check both the 65 and 66 degree switches for breaking contact above 65/66 as well as getting contact back above 65/66? I would also slave a Relay Box in and see what happens. I'm thinking it's possible that the TD system stays in Temp Controlling mode even below the useful range of the coordinator potentiometer, causing the amp to go to full take. The popping could then be caused by the engine dropping below 94%.

Don't forget the "Flag" check. Upspeed the engine, then put a rag secured to a seat rod up in the left and right bleed collectors and see if the rag whips around, indicating an open bleed air valve.

--------------------------------------------------------------------------------

pjvr99

As a side-note, I have a direct-reading gauge hooked up to the bleed valves during all

runs on the cell. I had an engine surging intermittently, mostly during throttle back,

but all throttle settings, and sometimes even at stabilized throttle setting. Eventually,

during man-on-stand, I heard a puffing sound, and put my hand in front of the speed

valve. Installing the gauge showed a momentary drop of up to 30psi, thereby opening

the bleed valves.

Since then I have found that a difference of more than 10 -15psi between CDP and

speed valve pressure is enough to momentarily pop the 10the stage valves during

some throttle movements

Lquest has asked a good question on the rich/lean, and the cross-over correction

--------------------------------------------------------------------------------

sharif101

yes, i checked coordinator both 65&66 degree switch.relay box replace new one.now problem shifted today given ground run 2 times.TD null 3times check but 1 time flame out.last time when TD auto and throtle back to flight idle TIT 720 degree then flame out with sound at that time FF increase 500pph,TIT above 900 degree & RPM 93%.i think bleed valve open since RPM below 93%.is it FCU problem?ssv filter check ok.pitch lock regulator replace new one.Xover TIT 775 degree.

can i change acceleration bleed valve?

--------------------------------------------------------------------------------

tenten

I understand from the last last post that even in null the engine is flamed out; and that the RPM dropping to 93% just before the flame out.

To me once the RPM dropped to 93% and bleed valves opened it is normal to see what you have seen.

Based on that, I see no benefit of changing the acceleration bleed air valves.

It seems to me that the main issue is RPM dropping once power retarded; then the puzzle need to be answered;

Way at flight idle the RPM dropping below the threshold of keeping the acceleration bleed air valves closed (94%)?

Is it a fuel Issue (FCU lean) (blocked fuel nozzles) or a valve housing issue, or the low pitch stop setting is high accompanied with less fuel?

And I believe that the answer can be obtained from your engine instrument if you read and compare them with the symmetrical carefully.

One thought: Use the credit of the null orifice and let more fuel to go and see what will happen while engine bleed air valve in closed position.

--------------------------------------------------------------------------------

NATOPS1

Tenten has made a great recommendation. Adjust your TD valve null start temp UP to 810 (780-810 not a limit) maybe even 820? just make sure it is less than 830... Check your blade angle when it is on the LPS.

--------------------------------------------------------------------------------

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This is starting to look like a pitchlock problem. Try feathering the prop, place

throttle to flight idle and unfeather/airstart, see what the blade angle is. Alternately

during next run, if the engine flames out, place condition to STOP, do not FEATHER

or use emergency handle, and do not move the throttle from the position

the flameout occurred. Once engine has stopped, take a look at the blade angle

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