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nutmix

C20 R's And Compressor Stalls

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Hi to all,

 

We have been having a few case's of C20 R's compressor stalling recently. We only have them in NOTARS here but we are having different operators/maintainers experiencing them.

 

Has anybody that opeartes them been having any issues?

 

We have had a close call and an aircraft loss as a result of stalling recently.

 

We have also had a loss as a result of a #1 bearing failure a while back.

 

I know extremes in FCU derich and accel settings can cause them, but we have also had tight #1 nozzles causing them if the bleed valve is not set at the max settings for closing late and opening early after o/hauls.

 

Any info would be greatfull.

 

Thanks in advance,

 

Nutmix

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The C20R's i've worked on have for the most part been pretty fussy. Stalling or surging is not a nice feeling and have many causal factors.

 

I usually go right to the compressor and have a look. Is it dirty? when was the last WASH performed? How was the last power check?

 

A weak or maladjusted bleed valve can make the stalling more prominent once the clearances within the compressor are approaching limits. Even the inlet geometry of the a/c can have an effect on compressor airflow. Sometimes rolling the throttle on too quickly can cause the stall but if you are stalling while making large power changes say from pole down on approach to pulling up the power have a good look at the compressor/impeller. Have a good look at your engine component times, if one of them is approaching o/h maybe try that.

 

I

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The C20R's i've worked on have for the most part been pretty fussy. Stalling or surging is not a nice feeling and have many causal factors.

 

I usually go right to the compressor and have a look. Is it dirty? when was the last WASH performed? How was the last power check?

 

A weak or maladjusted bleed valve can make the stalling more prominent once the clearances within the compressor are approaching limits. Even the inlet geometry of the a/c can have an effect on compressor airflow. Sometimes rolling the throttle on too quickly can cause the stall but if you are stalling while making large power changes say from pole down on approach to pulling up the power have a good look at the compressor/impeller. Have a good look at your engine component times, if one of them is approaching o/h maybe try that.

 

I

 

Hi I,

 

Thanks for your feed back. I have been down the exact roads you are describing. The aircraft loss case had less than 300 hrs TTSN on the aircraft and engine...........

 

Stalling when rolling the throttle open, (different a/c) has been cured by changing the start derich and accel adjustments from extremes to a more neutral setting. Sometimes had to do and get a good start though.

 

Cheers

 

Nutmix

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Confirm by p/n that you have the correct bleed valve and FCU. I have seen standard C20B units of each installed on C20R's and both caused stalling issues, the bleed valve being the most severe. With the incorrect bleed valve the engine had to be accelerated VERY VERY slowly to prevent stalling. The C20R bleed valve is noticeably larger in size when compared to the C20B unit so it can be easily identified.

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I used to work on a Twinstar with C20R's. The No. 2 (LH) engine used to stall on startup all the time. Everyone said it was normal due to the airframe configuration. I took their word for it and never did bother to troubleshoot. I guess I should have in hindsight.

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