The mega Ski Jump in Burnout paradise can be found on the Big Surf Island. The Crash TV Air Time Achievement / Trophy can be unlocked if you have a 4.5 second airtime on this mega jump.
To find the Ski Jump, start at the junkyard in the south of the Big Surf Island. Follow the Grange Hill west and enter a dirt road straight ahead. Follow it and turn left to find a huge Ski Jump banner. Make sure you have a full boost and a good amount of run-up before the ramp to reach the 4.5 second air time. This should be enough to unlock the Crash TV Air Time Achievement / Trophy on the Ski Jump.
Crash TV Air Time (Achievement / Trophy)
Land the Mega Jump from the Crash TV Ski Jump and get at least 4.5 seconds of Air Time