Tracer darts are a lot faster in Bad Company 2 post-patch so if you’re flying a helicopter make sure you have smoke to disable any tracer. Seems to be some concern that smoke in the PC version doesn’t work unfortunately. There’s also flares. This tutorial suggests,

The Blackhawk has anti missile flares that can be deployed by using RB if you have V ALT WEP equiped. This greatly increases its survivability because it makes it nearly impossible to hit with missiles if you spam your flares.

Geoff demonstrates removing tracers from a heli with smoke.