Ground operation with APUs
 

For ground operation of a Boeing or Airbus aircraft with fresh air supplied by the APUs, where is the excess air discharged - through the outflow valve(s), the pressurization safety valves, or both?

Door 1L

A320 on ground, the outflow valve fully opens, so that’s where the air goes if the doors are closed.

Very good!

🤣🤣🤣🤣🤣

On ground vs. in flight contaminant movement
 

The reason for my question is that I have been involved in some testing to investigate movement of virus particles on the aircraft. We have results on ground (with APUs) and in flight. In flight results show virus particles released in the back third of the aircraft tend to move toward the aft outflow valve, but on the ground, there is considerable movement toward the center of the aircraft (mix manifold). The in flight results make sense to us, but we are confused about the on ground results. Any insights would be helpful.

737s when sitting on the ground the pressurization panel would normally be set to ground mode which should put the outflow valve full open unless manually selected otherwise, so when air is coming in from either the APU via the packs or from the heat cart via the ground connection there will be a pretty much equivalent flow of air going out of the outflow valve instead of the cabin pressurizing. However, as mentioned farther up, I would also think that when any of the doors are open then a bunch of the flow would probably go out that instead based on path of least resistance.

A couple of questions about your ground tests...
Aircraft type?
Which doors were open?
Where was the wind blowing from?
Which packs were operating?
Were recirc fans in their normal config? (we turn certain ones off on the ground...)
So many variables!