Hi!
This from the pov of scheduled -121, from what I remember at TSA ground school in 2001.
The old way of interpreting the regs was legal to start a trip, legal to finish. That changed to a leg-by-leg evaluation at some point. The FAA re-interpreted their own regs and they were sued by the ATA which claimed that the FAA re-interpretation amounted to creating new regs. The FAA won, which is why the scheduled airlines now use the leg-by-leg method.
If your trip/day is scheduled under 8 hours, you're legal to start. Then, u have to evaluate each leg separately.
If, on your last leg, it should take you 45" of block time, and you block out at 7+00, u r OK as you would block in at 7+45. However, if you then took a 20" taxi delay, you CAN'T takeoff, as that would put you at 8+05 at the end of that leg. U have to taxi back to the gate and the airline will get a new crew to fly that leg.
Now, if you did block out at 7+00 for the 45" block time leg, and you took off normally at 7+05, and then, enroute, you took a 30" holding delay, for example because of ATC requirements, you would now block in at 8+15. In this case, U would be perfectly legal, because the delay was IN FLIGHT during your last leg and out of your control.
So, in both cases the answer would be no, you can't block out knowing u will be over your 8+00 when you block in.
This is what we were taught at TSA, which is a scheduled, 121 carrier. I now work at a 121 supplemental carrier, and they fly legal to start-legal to finish. They are allowed to do this either because it is supplemental, or our local FSDO allows it.
If it's only because our FSDO allows it, that is bad, because if something were to happen, then FAA HQ could easily violate the pilots and our co. by saying the FSDO was interpreting the regs incorrectly, and we would be screwed. This has happened recently with the charter/broker situation and what different entities are required/allowed to do with regards to flying charter PAX aircraft.
cliff
YIP
Note: I don't use the 121 regs with the aircraft I operate, which is why I don't understand the 121 vs. 121 supplemental differences situation so well.