We angage both auto pilots (airbus) for any non manual ILS approach flown because the FCOM says so. Simple as that. It has nothing to do with manual flying skills, lack of trust in the system as someone pointed to. It's airbus procedure and I have never seen any company not following this procedure.
FCOM Normal Procedures Aircraft Guidance Management:
BOTH APs ENGAGE
- When APPR mode is selected AP1 and AP2 should be engaged
Having said that, in FCOM AUTO FLIGHT FLIGHT GUIDANCE Appr mode there is a note stating "Second autopilot may be selected". May, not should.
As those of you flying the Airbus are well aware of the Land and Flare mode disengages if BOTH autopilots are disengaged and also below 200' RA the Autoland warning light is triggered if both APs disengage. In other words, with two autopilots engaged you will not encounter these issues if one AP fails. Although not required for a CAT I approach this could be the reason that Airbus sops calls for engagement for both APs? Engaging two APs every time you fly an ILS approach also streamlines sops for CAT I II and III operations of course.
CP