Thanks for the reference.

It evens out the emulsion layer by forcing it to flow downward just like a doctor blade does. A doctor blade is an actual metal bar that is a precise distance away from the moving emulsion layer and support and removes excess wet emulsion while it is still hot and mobile.

The air kinfe does the same thing, but has no contact with the emulsion layer itself. The air knife was not used by EK (AFAIK) but a lot of other companies did. Kodak used the doctor blade. There was quite a bit of difference of opinion regarding which method was best. IDK if it was ever settled, but both had advantages and disadvantages.

The excess emulsion either filled in uneven areas in the coating or it actually scraped the hot, wet emulsion back into the reservoir.