How to make parachuting tanks

[Maltesefalcon 0]

I am attempting to make a BMD-3 Parachute down to earth, i am have to scripting for it to para down but when it comes down to earth it just cuts right through, so what is the command line for a trigger to be executed when a object reaches a certian flying hieght

[Trapper 0]

Try this for 500m height.

Condition: getpos tank select 2 < 500