Triggernometry achievement is possibly bugged

There is a description:
"Triggernometry: Shoot down an enemy support aircraft with an RPG."

As we understood it right, all mounted helis are classified as Attack Helicopters (e.g. Huey, Cobra, Loach) - shooting em down don't unlock an achievement.
So, then support aicrafts are Recon Plane, AC-47 Spooky, F4 Phantom. But if you shoot down a Plane, you will not get an achievement. AC-47 and F4 seems to be invulnerable, because they don't get any effect while got hit by DShKM or RPG - bullets are going through em. And I couldn't find any information about that in 1.01 changelog or in roadmap/forum bugreport desk/googlesearch etc.

Please if anybody have any information about achievement let me know.

Triggernometry achievement is possibly bugged