Do you remember when infantry could shoot down aircraft?

Oh don't surrender, you just have to be creative, doing it alone tho its very difficult, i recomend you getting at least one buddy,

the most basic (and easiest way to avoid), is using the stinger, its too easy to avoid if you as a pilot have the terrain in your advantage like a building or sand dunes can really be handy on an experienced pilot.

if you start shooting a pilot with a stinger on an open space, you will be targeted almost inmediatly since they have in game tools that can use to tell them the direction where the lock on is happening, after that, the pilot will pop his flares and run away from the danger to recharge the flares, that is where your buddy enters, 

• Identify the escape route of the helicopter
• get a player with another hatred for helis waiting there
• Shoot your stinger
• see heli ran away
• Get your buddy shoot a singer when the heli doesnt have flares, that will take 60% of the health
• hope for the heli to panic and score the second stinger
• extra points if 2 players shoot simultaneously at the un-flared heli

This will only work the first time, most heli tryhards adapt their routes, but constantly harrasing helis with that tactic will make their impact on the match be less noticable

lemme know if you want me to tell you more tactics for taking down helis