VL - I get where you are coming from - on the Mk3A Sea King we had an SN500 duplex AP, when selecting TAS hold for example, the PF would acknowledge coupled
in pitch, that was why I wanted to clarify the term - coupled
in Pitch or Roll or Yaw is quite specific to the AP channel, coupled to pitch is more ambiguous.
It does get confusing but going back to basics help;
Channel - PITCH about the lateral axis.
Channel - ROLL around the Longitudinal axis
Channel - YAW around the Normal axis.
These are Attitude modulations.
The commanded collective channel does not create attitude changes (intentionally) and is the oddity.