Strafer
I've never flown in an airline that has stipulated when the autopilot should go in or out and have never heard of ANY airline that does either.
The autopilot doesn't burn less fuel than me. If I'm climbing at ECON speed with the autopilot out I burn the same fuel as I would climbing at ECON speed with it in. The FMC gives me that speed and if I try really hard (
) I can just about manage to fly at that speed!
I do not tend to sit in the cruise with the autopilot out though, that just gets tedious, but I can do it if I choose to.
In the descent, the same applies as with the climb. If I program the FMC it will tell me where my TOD point is and I can then descend with the thrust levers shut A/P in or A/P out, fuel burn is the same. What screws it up are restrictions posed on achieving a constant descent with the levers shut, such as an ATC command to maintain a level. I can play with the speed to a certain extent to keep the levers shut whilst flying level, but if I have to fly level for any length of time I have to put the power up, A/P in or A/P out. If the FMC is kaput I use a rule of thumb to work out my TOD and with experience can end up on a 4 mile final approach with the power coming up for the first time ready for a possible G/A, again A/P in or A/P out. It makes no difference, except to my enjoyment level
.
The autopilot just follows an input. The clever stuff that works out the most economical way for the aircraft to operate is the FMC. That will tell you what FL to try and get and when, what speed to fly at and so on. I can follow those instructions just like the autopilot can. So there you have it, no restriction imposed by the airline, as long as I follow the SOPs and of course traffic and weather permitting (the PNFs duties are increased significantly if I fly with the A/P out) so it makes good sense to ensure that he is happy with the workload and on some occassions (POL departure off 32 at Leeds rings a bell) there is a very high workload in the first few miles so it makes sense to brief that you will take the A/P very early.
Another point that comes to mind is about the A/P flying a 'little bit straighter' than a human. I don't know if you fly or not, but anyone who does will tell you that it is a basic flying skill to be able to fly in a straight line and even I don't 'wander' that far off heading as to cause an increase in fuel burn!!!
Regards and happy flying.
PP