Can someone tell me why is this open during flight?

In the picture I posted if you look towards the tail of the plane there is a panel that’s open. Can someone tell me what this panel is? So my guess is it’s the apu bleed panel that’s open but why would it be open during flight is also my question. (Ignore the atc text box it was a busy day for atc).

I am not sure but I think it would be the outflow valve. APU Bleed Valve is inside the APU system itself.

Why would APU Bleed Air need a panel? APU bleed air goes towards the packs (then mixer unit and cabin), the starter valve (to start the engines), wing anti-ice (if wing anti-ice valve is open), water tanks and hydraulic tanks (if pressure is not enough) That’s all. (Check A320 APU F-COM)

Maybe Aernout could help us more,

Oh ok but I thought that when you turn on the apu you turn on the apu bleed which opens a panel in the back of the plane to let out all of the exaust? Correct me if I’m wrong because the closest I’ve gotten to anything close to real aviation is infinite flight so I wouldn’t know :).

When you press master switch:

ON appears on Master switch
ECB is powered
APU Flap Inlet opens
APU Fuel isolation valve opens
APU LP Fuel pump is powered by AC current
Shut-off Valve and FMV remain closed.

When I press APU Start switch:

ON appears on APU Master Switch
The starter is powered
1,5 seconds after starter is powered, ignition starts.
FMV and Shut-off valve open.
At 50%N (or 60%N), ignition stops. Starter is de-energized.

When APU reaches 99%N or 95%N + 2 seconds, APU Gen line contactor closes (if EXT PWR Switch is OFF). APU Bleed Air Valve can also be opened by the APU Bleed Air switch. (Note: If APU Bleed Air switch is Open, X bleed valve is open and Engine bleed valve is closed).
AVAIL appears on APU start switch.

Check F-COM, everything is there! :)

Note: This for the 320. Maybe Aernout or a 737 pilot could help us more.

Ok thank you I’ll be sure to check the f-com to see if I can find out what the open panel is.


Here is the outflow valve on 737 :)
It looks like it’s the same on your photo!

What is the purpose for the outflow valve?

It controls cabin pressure!

As altitude increases, pressure reduces. I think you lose 28hpa every 1000ft (will have to check back). So the outflow valve controls pressure in the cabin. There are also safety valves. The outflow valve and the safety valves are controlled by the Cabin Pressure Controller (CPC). There are 2 CPC in the 320. 70 seconds after landing they change the controller (ie. If CPC 1 was controlling the outflow valve, 70 seconds after landing, CPC 2 will start controlling the outflow valve).

You can also control the outflow valve by the cockpit (eg. CPC fails).

Hope it helps!

Ok thank you for the help I was wondering what it was and you did a great job explaining it to me so thank you. Now on the topic of a320 hopefully the a320 update comes out soon ;)

Yes, this is definitely the outflow valve.

My pleasure :)

Sorry, I could not help you for the 737… I don’t know much about Boeing systems but the concept should remain the same!

Yes, just waiting for AF’s A320 familly on IF :)


Same I can’t wait because the a320 is one of the most used aircraft in the world and many flights in real life use the a320 so I can’t wait to finally try it out.

Yeah @AF330 explained it to me already but thank you anyway for checking out my post to help me :)