You shouldn't have much problem unlocking this achievement if you plan on completing the game but if you're looking up the solution, it means you're either confused by the description or you want to know a quick way to unlocking this. I have only unlocked Season 2 so I haven't really made it that far in the game so I just found a spot and I replayed the race over and over until the achievement unlocked.
The second race of Season 1 is where I grinded out the achievement "Tokyo". I was also using a Class D vehicle that I was trying to upgrade all the way. So enough with my rambling I will say which path I took to getting my achievement.
JUMP #1 - So once the race starts, save up your boost and when you have to take a left turn, go to the road on the right. There will be a jump which you can take over a bus. You should get about 1 second from the jump.
JUMP #2 - Now once you go left a second time, you will see a jump on the left side of the road. Take this with your boost to get 2 or 3 seconds of Air Time.
JUMP #3 - Go through the building right after JUMP #2, located in the middle. You can either go left or right, choose to go through the middle. You will only get a second out of this jump but hey, every second counts. You should be around 5 seconds now.
JUMP #4 - #7 - It's important you go right now as you will get a lot of time here. There will be a light shining in your eyes, but after that goes away there will be a jump to your left and right, take the right jump. After that, put your vehicle in the center of the road to prepare for the 2nd jump. Hit the 2nd jump and now prepare for another jump on the right side of the road. Hit the 3rd jump and just like before, prepare to hit the 4th jump in the middle of the road. Once you hit all 4 jumps, you will be around 15 seconds or Air Time.
JUMP #8 - #9 - Go a little ways after jump 7 and you will see a road blocked off to the right. Take that route and you will hit another jump, right after this jump, you will hit a 2nd jump. Be careful as it's right next to a wall and you don't want to crash here. Once you hit both jumps you will come to a robot, go under it and follow the road ahead. You should be at 20 seconds of Air Time now.
JUMP #10 - #14 The final jumps can be a little tricky to not crash at so just make sure you always save up your boost and use it on the jumps. Anyways, use your boost to hit the ramp, then boost again to hit the 2nd jump, same thing with the 3rd jump just use your boost, once you hit the 3rd jump and land, you're safe to go. Hit the last jump to make it back on the road and finish the race up.
The race isn't that long and you can get anywhere from 20-30 seconds depending on what vehicle you use. The achievement is cumulative and counts for all vehicles. You don't need to worry about anything besides Air Time. It doesn't need to be in one sitting or with one vehicle. Good luck and I hope this helps :)