The gate in mission 3 is a rather flawed trigger. Mainly because it isn't one. If in Single Player on this specific map your position and angle are checked. If all pass you go through that special animation and land. The flaw is that it doesn't check any of these things when doing a barrel roll, a loop, or a U-turn. So by boosting and preforming a barrel roll at just the right time we can complete bypass the "trigger".

I discovered this recently on my own, but it was actually discovered ages ago. A YouTube video with an 8 month old comment on a YouTube video with this ID: plVtVPWBwGo was the earliest I thought it went. Apparently after asking the Japanese runner Maruga it seems to actually date back to March 17th 2005 on a Japanese site called "wazap". It was documented by someone named "techno" according to Google Translate (Can't put link here or post won't save).

Anyway this video will show this exploit in a practical sense to improve the speedrun for Mission 3 bronze. This is a LOTAD (exploit at 0:47):