You've stumbled on a pretty old wish that divides the community, sherman! Somebody suggests it every now and again.
Lots in the community see it as a 'power up' of sorts, and it strikes them as gamey to have a missing elevator or rudder replaced, pilot wound cured, or fuel leak repaired while sitting in a repair area of a hangar. Since it couldn't be done in a small time frame in real life, it shouldn't be possible in the game, they reason.
For me, I would get some satisfaction landing at a field and being able to taxi to a hangar and then spend some time and/or perks to have my aircraft fixed (would be nice to be able to change the loadout here too). That strikes me as more immersive, and carries the risk of being vulched while on the ground, adding to my interest.
As far as pilot wounds go, whether you tower out or use the repair hangar, either way you're going to be healed- so isn't the more realistic alternative the one that requires at least some recuperation time?
And they are right HTC has said no to the idea before, so s'all good.
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