It has always been a grey area with no definate black & white document that I know of... We put all our trust in the engineers and believe what they tell us.
I am 2 days flight away from our engineers so I'd like to know where the line is. The examples I gave - actuators depleting... do I ground the a/c and wait 2 days for someone to come replenish a little or do I wait till it is really needed...if so, how much is enough to stop. Fuel pump 2 is blown on an AS350B2 with 2 pumps... I can still fly with one... just examples of mechanical snags I've had in the past.