Quote : "
After takeoff, CLB is automatically engaged."
NO, in normal OPS, with the FD on, autothrust and CLB are armed -
A/THR and
CLB are blue on the FMA. The PF selects CLB by pulling the T/Ls into the CLB detent, at the same time making the A/THR active.This happens at your selected "Thrust reduction altitude", at which you'll have a flashing "
LVR CLB" reminding you to set the T/Ls into the CLB detent, thus activating the A/THR.
A/THR will go white on the FMA.
Quote :"
Do you also have to *manually* engage the AP to engage NAV mode, or does it automatically engage at a certain altitude?
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No, NAV mode is armed during the take off and engages automatically at 30 ft, so that one could follow the SID manually. Engaging the A/P only means that it will take all the FD engaged/armed modes into account, as the modes are common for both FD and A/P.
Quote :"
Then, in the climb phase, does the PF have to manually keep the AoA to whatever angle is prEscribed, or is that then automatic as part of ALT or CLB (ie, at thrust reduction and accel altitudes is the pitch then automatic)? "
After take off, the FD would give you an initial climb at V2+10 Kt or above, speed that you'll maintain with the FD bar until the end of the noise-abatement ; then the FD bar will propose a lower pitch angle in order to allow acceleration and cleaning-up after which a 250kt climb will be established.
The AoA requirements are translated for the pilot -whether flying or monitoring the A/P - into speed schedules and FD/Ap commends.
Quote :"
If the pitch has to be manually kept, surely that would disengage the any APs that are active?
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You could, if you wished, engage the A/P as soon as 5 seconds after lift-off or 30 ft radio height. in this case, the A/P will do a very good job of maintaining the climb parameters of the day. No need for human intervention. On the other hand, if you elect to fly manually with the FD, the command bars will give you the optimum performance for your take off segments.