Schatzi commented above:
The problem with a training base in the MA is simple. Damage/Killshooter. The first thing a newbie usually wants to do is get in the air and shoot something.
Fair enough. I've had a few more thoughts and I think it would be possible to let the Training Base's "radar circle" control features specific to the Training Base.
Only for planes that spawn from the Training Base and that stay within the radar circle:
"Kill Shooter" is OFF
"Invulnerability to weapons fire" is ON
"Lead Angle" aiming is ON
As long as the instructor and newb stay within the "radar circle" they fly pretty much as in the TA. However, only the planes available in the arena are available at the Training Base, and perk planes still cost the same amount to fly. So if a newb with no perks wants to fly an ME 262 they have to go to the TA.
Vets who want to refresh a few minutes in an unfamiliar plane would be able to do so in the same arena just by moving to the Training Base. I'd set a max limit of 15 for access to the Training Base by vets who are neither instructors nor newbs to prevent turning the Training Base into the center of attention of the arena.
If planes that spawn from the Training Base leave the radar circle, then kill shooter goes back on, vulnerability to weapons fire is on, there's no lead angle, and if they shoot down an enemy plane outside the circle, they get negative perks. This discourages using the Training Base to mount offensives.
Enemy planes that enter the Training Base radar circle may be attacked by anyone who spawned there, who have the advantage of kill shooter off between them and invulnerability to weapons fire. That discourages but does not prevent enemy over-flights of Training Bases.
A friendly aircraft from a different base that crosses the radar circle is subject to "lead angle" aiming, friendly fire shoot down, and cannot shoot down Training Base planes but is still subject to kill shooter. This discourages but does not prevent allied planes from loitering over the Training Base.
I also thought that if a new subscriber of up to ~ 3 months moves to the Training Base, and no instructors are there, then the Training Base could flash Blue on the clipboard map. This would alert instructors and anyone else that a new subscriber may be looking for help.