Here is the full list of all 52 Altitude achievements. It takes around 12-15 hours to unlock all of the achievements on Windows.
Shoot down 50 enemy planes
Shoot down 100 enemy planes
Shoot down 150 enemy planes
Shoot down 2 enemy planes within 4 seconds of one another
Shoot down 3 enemy planes within 4 seconds of one another
Shoot down 4 enemy planes within 4 seconds of one another
Shoot down 3 enemy planes without dying
Shoot down 6 enemy planes without dying
Shoot down 10 enemy planes without dying
Interrupt an enemy's afterburners with Loopy's EMP grenade. Easy peasy lemon squeezy.
Complete Training: Air Ball
Complete Training: Multiplanar Mayhem
Complete Training: Nuclear Launch Detected
Complete Training: We Fly High (Ballin)
Complete Training: Splanelunking
Complete Training: Pilot Certification