I think a free month or two with an advertising push would help. Get them hooked, keep them around long enough to learn the basics. Then they pay.
Or they could make the training arena free
Hear me out on this, just a spitball: The current way is that the new player gets two weeks automatically free w/no strings attached. But they wouldn't be able to find the time or the money to use it properly(school, work, etc.). By the time the new player finally makes time, their two weeks are up, and have to pay to learn how to fly, fight, voice/text comms, the essentials to play AH, and that kinda demoralizes the new person, therefore making the decision to go to other games that can meet their needs(War Thunder, WoT, WoWP, etc.), making AH look bad.
If the training arena was opened up freely to new players without the need to limit it to a number of days, weeks, whatever...this way, new players would be able to find time not only to learn the basics of flight simulation in AH, but also interact with one another and know what it's like to have fun, maybe even look to join up with known squads BEFORE they get into the arenas and events. Then, once they've mastered the fundamentals and scooped up enough money for each month, then they pay to enter the arenas to play with the big dogs.
That's just my thoughts on the matter.