Handler.java

public class Handler {

    @SubscribeEvent
    public void onEntityUpdate(TickEvent.PlayerTickEvent event){

        if(event.phase != TickEvent.Phase.START|| !event.player.worldObj.isRemote) return;

        if(event.player.getCurrentArmor(2).getItem() != doPreInit.fairysunwings){
            if(!event.player.capabilities.isCreativeMode) event.player.capabilities.allowFlying = false; event.player.capabilities.isFlying = false;
        }
        else {
            event.player.capabilities.allowFlying = true;
        }
    }
}