Here is a very simple instruction
http://forum.1cpublishing.eu/showpos...6&postcount=95
You can start with it and then add 5 or 10 more sub-missions with various loading loops/cycles in the same way to have random flights which overlap in time.
When you try this if it is not enough you can ask for a more complex script with true randomization. (I am not a C# programmer, so you do not have to be afraid of scripts either.)
Please let me know if you try this.