Looong Waaay Down! 5
Be Airborne over 13 seconds
Go to the stage "The Far East" and select the vehicle Rad Hazard. You will come to a huge waterfall. Jump off the Waterfall and let off the boost. you will hang in the air for around 16 seconds.
I do not believe this is correct. I did this several times and landing at the rock pole didn't get the cheevo.
I jumped the waterfall and left the boost on. I landed where the two boats are just sitting in the water and the cheevo popped right away.