Thanks 
In your example when you have all failures set to 33% and lets say you have both random alt and time. When you click “Start” button then app rolls dice which failures will happen with 33% chances for each failure
33% is quite high so if you have all failures with 33% and you dont set “Limit no. failures” then you have high chance to have few failures
At first there is rollig dice which failure will happen with 33% chance. Lets say 10 failures were randomized. Then there is second randomization: what will trigger each failure: time or alt (only two so 50% chances for each)
Lets say it was even: 5 failures will be triggered by time and 5 by alt
And then there is third randomization for each failure: at what exact alt or time failure will trigger
Lets say you set alt range between 2000 and 3000 (keep in mind that this is absolute alt. If you are on airport that have higher elevation than 3000 then all alt failures will trigger instantly). So for each of that 5 failures there will be selected alt at which (or above) failure will trigger. One can trigger at 2154 ft other at 2837 ft, etc.
For failures which will be triggered by time there will be randomization at what time after takeoff failure will trigger. Of course between set time range
You can check it all on “Failure list” tab. There will be list of all failures that will trigger (or triggered already) and there will be information what will trigger it
I have in my mind something like wear and tear. However I will see if I will add it to RandFailures or if I will make completly new app for that. For now Im rebuilding RandFailures to make it more user friendly and easier to maintain