Bleeds closed CRJ-900

S

STS-41B

Well-Known Member
If we have to do a bleeds closed takeoff.. we leave APU on. Problem solved. .. (unless of course once shutting it off the door doesn’t close.. had that happen several times)
This probably is a stupid question.. but why not just turn the bleed switch to “off” on the overhead panel?
And if APU is in-op, why not do that instead of doing an unpressurized takeoff?
 
Because the pneumatic system is automatic (assuming you have the bleed valve selector in Auto mode). With both engines running and APU running, the APU will take priority in supplying bleed air. The engine bleeds will will automatically close because the APU takes priority in supplying bleed air if left in auto mode thus there is no reason to move the bleed valve selector to closed because in auto mode, the system logic will already do this for you.
 
Last edited:
I understand you don’t switch the bleed valve switch if the APU is running..
I’m saying, why not shut off the APU and just flip the switch instead??
If you’re doing an air-start.. you flip that switch to close the bleeds... why not for bleeds-off takeoff?
 
STS-41B said:
I understand you don’t switch the bleed valve switch if the APU is running..
I’m saying, why not shut off the APU and just flip the switch instead??
If you’re doing an air-start.. you flip that switch to close the bleeds... why not for bleeds-off takeoff?
Click to expand...

If you switch off the engine bleeds the HPV/PRSOVs close and if the APU is also off, you lose pressurization, ECS (packs), engine cowl anti-ice, wing anti-ice and bleed air for engine starting.

That seems bad to go flying like that on purpose. What am I missing?

 
STS-41B said:
If we have to do a bleeds closed takeoff.. we leave APU on. Problem solved. .. (unless of course once shutting it off the door doesn’t close.. had that happen several times)
This probably is a stupid question.. but why not just turn the bleed switch to “off” on the overhead panel?
And if APU is in-op, why not do that instead of doing an unpressurized takeoff?
Click to expand...
The 700/900 does it automatically for you. The 200 you have to do it manually.
 
STS-41B said:
If we have to do a bleeds closed takeoff.. we leave APU on. Problem solved. .. (unless of course once shutting it off the door doesn’t close.. had that happen several times)
This probably is a stupid question.. but why not just turn the bleed switch to “off” on the overhead panel?
And if APU is in-op, why not do that instead of doing an unpressurized takeoff?
Click to expand...
I mean if you wanna do the, "stupid question" thing ill give ya the easy answer. Because ur book tells you how to do it. As was said turning the bleeds off just causes a crappy unpressurized takeoff and why do that to anyone if you dont have to. Even if the apu was out youd open that ram air sov and give the pax some limited ram air press that'll take the edge off. Ask one of my old captains on the 1900, he had every thing setup and i shut off the ram air and whoo weee Rick did that hurt the ears. Next time we did it the book way and it helped.

Anyway, just do what the book says or live to regret it and tell stories. Ask some of the edv guys about that little bleed off cowboy procedure when one of our resident goofball LCAs saw it. Whoo wee Rick, fireworks at the next standards meeting.
 
This is also a slight hold over procedure from the -200. There was no automatic bleed logic on that airplane and, it was possible (actually, probable) that if you didn't reduce power before switching the packs on after an Bleed Closed takeoff, you'd over pressurize them. Keeping the system in automatic on the 700/900 was a way of preventing that from happening as, when switching from the APU to the Engine bleeds the software commands a gradual opening of the engine bleed valves to allow the PRSOVs to modulate and protect the packs from an over pressurization. If you have the bleed switch in closed (off? I can't remember... it's two airplanes ago) and throw it back to automatic, the engine bleed valve opens quickly as the system logic isn't there to protect anything. When that happens the packs can overpressure and die.
 
BobDDuck said:
This is also a slight hold over procedure from the -200. There was no automatic bleed logic on that airplane and, it was possible (actually, probable) that if you didn't reduce power before switching the packs on after an Bleed Closed takeoff, you'd over pressurize them. Keeping the system in automatic on the 700/900 was a way of preventing that from happening as, when switching from the APU to the Engine bleeds the software commands a gradual opening of the engine bleed valves to allow the PRSOVs to modulate and protect the packs from an over pressurization. If you have the bleed switch in closed (off? I can't remember... it's two airplanes ago) and throw it back to automatic, the engine bleed valve opens quickly as the system logic isn't there to protect anything. When that happens the packs can overpressure and die.
Click to expand...
Rapid and high amplitude thrust lever movements on short final approach in a single pack configuration on the -200 will cause the remaining pack to trip.

I do not want to talk about it.
 
Autothrust Blue said:
Rapid and high amplitude thrust lever movements on short final approach in a single pack configuration on the -200 will cause the remaining pack to trip.

I do not want to talk about it.
Click to expand...

Meh... the plane should be unpressurized by then anyways. Other than a nuisance chime (and no coldish air once you land), it shouldn't be an issue.
 
BobDDuck said:
Meh... the plane should be unpressurized by then anyways. Other than a nuisance chime (and no coldish air once you land), it shouldn't be an issue.
Click to expand...
Ah, I forgot to mention "Atlanta" and "summertime" and no APU and aforementioned dislike for sweating, but agreed.

Much more concerning were said thrust lever movements, but moving on. The pneumatics on that airplane are a bad system.
 
Speaking of, company put out guidance for hot weather gate ops for the 200...APU LCV closed, and left pack off...apparently this tricks the system for better cooling with ground air, tricks the system into what?
 
I used to do something similar in the 200. On the ground with the APU off and ground air connected, turning the right pack on almost doubles the airflow. I have no explanation why, but it worked, and nothing with in our manuals was for it or against it.
 
Finny said:
Do you even remember how to spell CRJ anymore?!?!
Click to expand...
All I know, is that you need some good sweet mainline loving, and I'm looking forward to it all happening.

Someday you and I will play trumpets together. Then we're gonna see who shoots handguns straighter.

Hint: the monkey always wins.
 
jynxyjoe said:
Literally the first "trick" you learn on the line after sims. Yes it is sorcery, but it works so shaddap and do it
Click to expand...

Total baseless speculation on my part, but could it be that the right pack is closer to the distribution manifold and thus the air gets the “path of least resistance” into the cabin? :)

1565545143150.jpeg
 
You must log in or register to reply here.
Back
Top