Flying Tigers: Shadows Over China

You can get this towards the end of mission 'Railroad Mandalay'. Continue to progress until your objective is to 'Destroy the Grounded P40' that you previously had to protect. As soon as you gain control of your plane, accelerate relatively high above the objective, then when you feel you have enough height aim down and press to trigger the slow mo and just blast the objective holding the fire button . When the plane is destroyed you should instantly receive the achievement.

Here is a short visual for reference:

I did this in single player in Dogfight.

I chose 10 planes so I had a lot of targets, clear day so you can see. Also choose a map that is relatively flat like Toungoo so you can see better too. Have the enemy use a sea plane so they are slow. Now for your plane pick the P-80A Shooting star. Its like the 2nd from last plane. This plane is extremely fast and its guns are extremely powerful. I flew around and shot at all the planes until they were smoking. Then I flew straight up as fast as I could til I hit 15,000 feet. Then I immediately dove straight down and started firing at the planes that were smoking. Took me two diving kills to get it.

quick n easy method if you have a friend with the game.
this is how i got it.

host private match dog fight
invite friend
pick a decent aircraft like p98 lightning or whatever your comfortable with but found this one went up to around 12k feet.
get them to pick something nice n slow maybe one of the seaplanes.

get to as high as possible
wait to you see the red marker on your radar
dive down towards enemy blasting away and use the slow down function if needed.

now doing this hopefully you should shoot them down, now if they are only damaged or not at all climb to altitude and do again

now this is what happened with me i was diving down blasting away, my target was flying low over the water and crashed....achievement popped.
i don't think i shot him at all. so maybe worth giving that a go. it might be because he was destroyed whilst i was diving and targeting it counted.

XXXXXXXX EDIT 21/01/18 XXXXXXX
i just helped another gamer get this achievement by me crashing the target aircraft, just as described above. they got to +10k ft dived at me hit me once or so, i then crashed on purpose. achievement popped. so private 1v1 dogfight crash method works.
XXXXXXXXXXXXXXXXXXXXXXXXXXXX

obviously this can be done in multiplayer join one of the lobbies and follow the same instructions, gain as much height as possible dive down blasting rinse n repeat and you'll get it.

good luck and if you need a hand and i'm free gimme a shout

Map: Phi Phi Island
Aricraft:
Person going for the achievement: P80 Shooting Star
Partner: SC-1 Seahawk (Any Sea Plane)
Game Mode: Dog fight 2 players (private)

Once the match is loaded have the person in the sea plane land on the water in front of an island or any easy to recognize location. This is important because once the plane is on the ground it will not show on the map due to being below the radar. This achievement can be achieved on any level where your partner can land and be stationary.

The person going for the achievement locate where your partner is and fly up to over 12,000 feet. Fly straight down to the general location of your partner. The arrow will show when you get close, but it might not. Shoot until the plane is destroyed and the achievement should pop.