Full Ace Combat 7 playlist here:https://www.youtube.com/playlist?list=PL1nCuO5R6HvE8NilM7kYk...
This achievement is for completing the twentieth mission of the game and can be obtained on any difficulty.
Here's my playthrough of Mission 20 Dark Blue.
Aircraft used: F-22A
Special weapon: 8AAM (8 air to air missiles)
Score required: none
Time limit: First section 25:00 / second section 10:00 (Normal)
The objective for the first section is to shoot down two ADF-11F Raven drones. The only aircraft you need to eliminate are marked with a red TGT. This may take some patience but isn't particularly difficult.
The second section starts when you down the second drone. It ejects a smaller ADF-11F drone that will fly into an undersea tunnel to the Space Elevator. Follow it in but be aware that once inside, the drone will start shutting tunnel doors. Make very gentle adjustments to your course using the yaw (LB/L1 or RB/R1 buttons) and braking as required. There are checkpoints so if you do mess up (as I did), you can try again.
Eventually you'll reach an open area at the base of the Space Elevator. You now have less than 60 secs to eliminate all targets. Go straight for the ADF-11F drone and then the Repeaters. The timer stops and you need to move into the shaft in the middle of the Space Elevator to escape. Again, fine movements are all that are required to navigate out.
Congratulations, you've completed Ace Combat 7!