

Of course when starting Trucking, it's kind of hard to start e.g. Trucking and Quarry) have a bit of a delay between starting the mission and setting $OM=1, allowing for a very short window of opportunity (as in under a second) to start another mission. While all missions check if $OM=0 before they start, not all are the same when it comes to setting $OM=1 when they are started. Missions include not only story missions, but also side missions like Quarry, Trucking, Races, Vigilante and so on.

As long as $OM=1 then the game will not allow you to start another mission. passes/fails) it is set to the value 0 (false). When a mission is started it is set to the value 1 (true) and when the player leaves a mission (e.g. The game uses a variable called $ONMISSION (or short $OM) to track whether the player is currently on a mission or just freeroaming.
