A320 airflow change at roughly 2-3,000ft

[applecrumble]

Hi there,

I was flying an A320 the other day and on approach at roughly 2-3,000ft there was a fairly significant change in airflow sound. I was wondering what was likely to have caused this, I haven't noticed it before but perhaps this was the bleed changing from intermediate to high pressure bleed?

Cheers,
apple

[eckhard]

Something to do with the forward outflow valve, I believe?

[Goldenrivett]

Hi there,

I was flying an A320 the other day and on approach at roughly 2-3,000ft there was a fairly significant change in airflow sound. I was wondering what was likely to have caused this.

Hi applecrumble,

You probably heard the fuselage drain valves (https://safetyfirst.airbus.com/app/themes/mh_newsdesk/documents/archives/residual-cabin-pressure.pdf) opening. See page 3.
”Cabin fuselage drain valves :
A number (approximately 15) of piston-type drain valves are fitted along the bottom line of the fuselage, to drain condensation water or other fluid leaks. They close when ∆P between the cabin pressure and the outside ambient air pressure exceeds a certain value (between 1 and 2 PSI, i.e. 70 to 140 hPa). But their effective section is small (about 50 mm2 each).”

[applecrumble]

Thank you so much guys! Always learning.
Here’s a picture: https://aviaforum.ams3.cdn.digitaloceanspaces.com/data/attachment-files/2019/07/1423072_e53a61832f56d2b3a8711c56184c94f1.pdf