Indirect impact systems often have a small direct impact point.
For example, a chilled water system does not come in contact with product. Typically the chilled water will cool a tank, and so the temperature of the chilled water is critical, but not the chilled water itself. The temperature sensor(s) of the chilled water is product impact, and also maybe the flow meter(s). Thus qualification of the chilled water would focus on the calibration and use of the temperature and flow sensor.
Another example, might be the shell side of an autoclave. It is not product contact, but affects how the temperature in the autoclave functions (and uniformity, etc.). Thus there are parts of the shell which should be qualified, just not materials of construction, and weld inspection, etc - unless you suspect the shell isn’t 304 or 316 SS.
About your autoclave question - autoclave validaton is what started validation field in general (due to hard done for unsterilized equipment in hospitals, I believe). WIthout further information, the autoclave is likely direct impact. The room air could also be considered direct impact (because it touches the autoclaved items).
FYI, if you are autoclaving items, you shouldn’t move them “down” a classification area, and then “up” a classification area (like moving to different areas within a plant). Going from D to E (in this example) you have to assume the autoclaved item is only as clean as the E zone, after it has entered the E area.
That being said, you can move items in/out of classification zones, if you have removable protective bags around your items, and proceduralize how bags are removed and how items move throughout a plant.
So yes, your air in your plant is direct impact, especially considering sterilized items coming out of an autoclave.