Drawing aircraft from the pool

[jgsIII]

Can somebody tell me what condition need to be true for an air unit to draw planes from the pool? Not played AE that long but I keep seeing air units that show plans in the pool but the can't draw them. Thanks.

[Gary D]

Once per week I believe. 20K supply, or within range of an air HQ that has 20K supply.

[PaxMondo]

Can be less than a week if in training mode I beleive....and max of about 10 a/c per draw.

[jgsIII]

So you guys are saying, stay near a well supplied Air HQ (does affiliation matter?) and be aware there may be time limits. 
 
Let's see how that works.  Thanks guys...