Thanks all, some very interesting points made, particularily with regard to ACARS and the potential 'manipulation' of.
I suppose that the responses pretty much back-up my initial comment that there is very little or no consistancy in relation to this. In my extremely humble opinion there should be a standardised and regulated practice in relation to this issue, as it is (safety aside) the MOST important aim of aviation, particularily for low-costs whose whole existance is based on primarily two things, ancillary revenue and OTP. It shouldnt come down to things like how well someone gets on with a captain, or ways to 'cheat the clock'.
Therefore it should probably be more 'transparent', admittedly some delays are very convoluted with so many parties involved in a turnaround of an aircraft, but if everyone is confident of at the very least a 'true' ATD, then thats a starting point.
At the end of the day if something involves financial reproach then the waters will inevitably be muddied.
