[Konstantinos]

Why a for loop?
Just check if the player's is over x meters. And it may fail if you do sky diving from the highest tower on LS.

pawn Код:

stock IsPlayerInSky(playerid)
{
   new Float:x,Float:y,Float:z;
   GetPlayerPos(playerid, x,y,z);
   if(z >= 100) return true; // Change the value.
   else return false;
}