CRJ Systems

[hmmm]

The following... is just the point " Separate the need to know from the nice to know and focus on the former. It will make your life as a pilot a lot easier. "

In the Oral / Verbal they ask the question put forth here. Thought someone might know the answer and be able to explain it better than the check guy who it explained it to me. ( different from the oral guy) The procedure has not changed. Only the book was missing the step and now the step was covered. It was always taught the same way. Just not in depth in ground and then comes along an examiner and asks you the question on your oral.

Thanks for the time to make a well thought out response. The exert about being an A&P I.A. was only to give depth that the person asking the question does have a decent understanding of systems and being an A&P the Oral guy expects me to know a little more about systems then the rest so says he.

So... any understsanding in this arena?

 

[KingAirKiddo]

Ouch...my head hurts!!!

Hmmm,

First of all, why do you have to ask such difficult questions? I'm going to have to take some Tylenol to get rid of the headache brought on by racking my inept brain for an answer to your question

Our study guide says the following...maybe it will help you visualize what happens, maybe it won't:

1. All valves associated with the 10th stage bleeds are spring-loaded CLOSED and require air pressure for them to move open.

2. On the entire Bleed Air panel, the L & R 14th stage valves are the only ones that are spring loaded OPEN, and they too need air pressure to move closed.

3. Because all valves need air pressure to move them, they do not always move when the appropriate switch is pressed. It is easiest to remember that when the switches are selected, IN is OPEN and OUT is closed. The vavlves will move when the air pressure reaches them.

The book also states that for a crossbleed start the operating engine's RPM needs to be at least 85% N2 or higher, so that would be another way to indirectly check for appropriate pressure without actually checking the ECS synoptic page.

So in other words, the 10th stage ISOL valve is normally closed to separate the left and right side distribution ducting. It opens automatically during engine start to ensure a supply to both engines, regardless of pneumatic source.

Hope all this helps...think I'll go apply a cold washclothe to my head now.

 

[hmmm]

Yes, KingAirKiddo, That was a very good post and answer. Yes ahahaha I know it is hard to read how I write. Might need to apply a cold beer and aspirin with that cold washclothe to your head. Thanks for the reply and answer.

------

The one remaining question is that of the 14th stage valves.

If the 14th stage valves are pneumatically closed and are spring loaded to the open position..... Reason being they are set up this way so if somehow maybe if the wire going to them broke that you could still get air to the Anti Ice systems. Right?

Well in our book it has us make sure that the 14 stage PBA's are pushed in (open position).

Well I was told that the reason we make sure they are open are to help ensure against a hung start if we were to loose electrical power........... This comes from a very highly technically oriented check airmen at the top of the seniority list (not not JH at Pinnacle) of which I have a lot of respect for.

 

[KingAirKiddo]

Hmmm,

I'd agree with the first part...it sounds logical to me.

I'm not really sure on the hung start theory though...I'm having a hard time visualizing what he is talking about. I'll read back through some of my stuff, though, and if it "clicks" for me I'll post another reply here.

Take care,
KAK

 

[hmmm]

Yes I don't understand the hung start protection theory either on the 14th stage valves.

He said it twice so I am sure that is what he said and I heard someone else mention it before as well.

"Did we land or were we shot down" hahahaha I like that quote.

 

[DoinTime]

Maybe there is a bleed relief valve beyond the 14th stage valve that opens during engine start to help unload the compressor. Obviously its not on the synoptic page because you really don't need to know about it. Keeping the compressor unloaded and spinning freely would help avoid hung starts and since the 10th stage is pressurized for the engine start it can't be used to unload the compressor. Pretty sad that none of the systems manuals provided to us have any information like this.

 

[regionalcap]

It is a shame that is used as an oral question. I have never seen that in our manuals.

 

[hmmm]

Ok fellas so the following is what we got here copying and pasting our posts together since I'm sitting here sick in bed. Maybe I'm sick for spending so much time with it hahahah.

I sent the following to be verified by a Bombardier Engineer to see wht he says. meanwhile anyone have any more comments, ideas or knowledge. Thanks for your help with this fellas.
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1. All valves associated with the 10th stage bleeds are spring-loaded CLOSED and require air pressure as well as electricity (electro-pneumatic) for them to move OPEN with their associated PBA pushed in. The 14th Stage ISOLATION valve operates the same way. Spring loaded closed when PBA flush/out and electro-pneumatically open when PBA pushed in as long as it has both electricity AND air.

2. On the entire Bleed Air panel, the L & R 14th stage valves are the only ones that are spring loaded OPEN when no electrical power and/or air pressure is supplied to them, and they need air pressure to move them to the CLOSED position when their PBA's are pushed OUT/OFF position. If they were to lose electrical power with their respective PBA's in the out/off position the would move to the open/on positon making 14th stg bleed pressure available to the Anti Ice system if needed if a wire to the valves were to break. With their respective PBA in the in/on position the valves are sprung to the open position with the electric part of the valve not being energized. We normally leave the PBA's for the 14th stage valves in the IN / ON position so as not to keep the valves energized to the closed position for no reason and so bleed pressure is always available to the Wing and Cowl AI systems. A reason to close them (PBA OUT) would be if there were a 14th stage duct rupture.

3. Because all valves need air pressure to move them, they do not always move when the appropriate switch is pressed unless there is electrical power to direct/energize them and air pressure to move them. It is easiest to remember that when the switches are selected, IN is OPEN and OUT is closed. The valves will move when the air pressure reaches them.

4. (Side note) The APU LCV valve never allows itself to be supplying APU air pressure lower than is being applied from a 10th stg engine bleed source. If during operation it senses 10th stg bleed pressure on the 10th stg duct higher than it is supplying it will automatically close regardless of the LCV PBA being in the IN/ON/OPEN position.

5. The left and right 10th stage engine bleed valves AND the 10th stage ISOLATION valve open automatically regardless of their PBA position (in or out) when the start button/PBA is pushed.

6. In a normal APU assisted start we have the 10th stg ISOL valve PBA in the pushed IN / ON / OPEN position even though it will open regardless of the bleed source (APU LCV valve or 10th stg engine bleed source) when pushing in the START PBA and is then closed PBA OUT position when transferring bleeds on TO above 1500 AGL to isolate the L & R 10th stage systems.

7. A cross-bleed start for the CRJ requires advancing the thrust lever of the engine that was previously started by a ground air-start cart (if APU INOP) until you get 60 psi from the operating engine. The only way you can read the psi is by going to the ECS Eicas page to see the 10th stg pressure by opening the 10th stage engine bleed on the operative engine to supply the 10th stage duct with pressure although the book calls for both engine 10th stage bleed valves to be open. Unless you do so by pushing in the operative engine 10th stage engine bleed PBA, there's no pressure indication on the EICAS ECS page. Once you've verified the pressure, on the eicas page you can then start the other engine (knowing you have sufficient pressure of 60 psi to be utilized for the air turbine starter).

8. The book also states for a cross bleed start that the operating engine's RPM needs to be at least 85% N2 or higher, so that would be another way to indirectly check for appropriate pressure without actually checking the ECS synoptic page and not requiring pushing in the operative engine 10th stage engine bleed PBA since it will automatically open when the START PBA is pushed in. But this is only for system knowledge since it is not according to the procedures laid out in the book.


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Question: In our line operation book (QRH) it has us make sure that the 14 stage PBA's are pushed in (valve open position).

I was told that the reason we make sure they are open are to help ensure against a hung start if we were to loose electrical power........... I also heard on the CRJ that the 10th stage is used for this and since the 10th stage is pressurized for the engine start it can't be used to unload the compressor.

This info in the paragraph above doesn't rest well with my present systems knowledge.

Most jet engines I have been involved with namely Pratt & Whitney JT3D-3b & -7 and JT8-7 through 200 series of which I was a turbine and compressor component buildup and assembly mechanic, test cell operator, and inspector as well as line A&P and I.A. and then Flight Engineer and then Copilot on have a Pressure Ratio Bleed Valve or Relief Valve which is open ahead of the diffuser section that is open during engine start to help unload the compressor keeping the compressor spinning freely to help avoid hung starts.

Can you tell me anything or can you refer me to anyone who can explain why the 14th stage PBA's are verified in the ON / OPEN position during Crossbleed beyond the fact that it calls for it in the QRH / line operations handbook.

Thankyou respectfully,
XXXXXXXXXXXX

 

[hmmm]

Answer from technical engineer at Bombardier.

14 stage has nothing to do with crossbleed start. No reason for it to be in the QRH under crossbleed start other than the fact that it is nice to make sure they are in the pushed in/ on / valve sprung to open with no electrical power to the solenoid open and failed to the open position if a broken wire.

14th stage PBA's pushed in all the time so solenoid will not be energized for no reason wasting operation of the solenoid and,

is Failed or Sprung to the open so 14th stage air always available to thrust reversers and Wing and Cowl Anti Ice and PT2 sensor.

Said thrust reversers won't even arm with 14th stage PBA's in the out position.

Only reason you would close them by selecting the 14th stage PBA's out is if you had a duct failure.

And compressor unloading to help prevent hung start is accomplished by the engine automatically adjusted Nozzle Guide vanes (NGV's)

APU LCV valve closes with the pushing in of a tenth stage engine bleed valve PBA button due to electrical interlock in the switches in the bleed panel not by pressure at the LCV valve.

If you want to do an APU air supplied engine start and a tenth stage engine bleed valve PBA is in the pushed in position the actual mechanical end of the LCV valve will not open even with the LCV valve PBA clicked in because of the electrical interlock between the 10th stage bleed valve PBA and the LCV valve PBA in the bleed air panel circuitry.

The starter and starter valves get their bleed pressure from the 10th stage pressure duct inboard of their respective engines 10th stage bleed valve. So if you were to do a cross bleed start and you needed to see how much pressure was being developed from the operating engines 10th stage bleed you would only need to open that 10th stage bleed to see the pressure being developed by that particular bleed and the 10th stage bleed of the engine you were going to start does not technically need to be opened. Neither does the operating engine for that matter except for seeing the pressure being developed by the operating engines 10th stage bleed since that bleed will automatically open when the start button is pushed in on the opposite engine. At that moment if the ECS page was up you would see the pressure flow through the 10th stage duct except the flowing duct pressure would only read aproximately 45 psi. Only the static pressure of the duct needs to be 80 psi before the star valve opens releasing that pressure to through the starter. The pressure automatically reduces due to the flow is now not restricted and is flowing through the duct to the other starter because the psi is not regulated by any means other than thrust lever movement. You wouldn't know the pressure bled down because the ECS page is not normally up because you are normally watching to see that the starter disconnects at aproximately 55% on the status page of the EICAS messages on
ED2

This all came from a discussion from an engineer today at Bombardier. Hey I am a mechanic at heart and needed someplace to write this before I forget it so I can copy and paste it to my notes when I get home.

Comments Questions Lamentations?

MDR