Synaptic Simulations - A220

Nice ChatGPT answer :joy:. But, yes, at 2000 ft the approach guidance switches from DMC to the Primary Flight Control Computers (PFCCs), so that is kind of accurate.

In approach mode, the approach guidance solely uses LOC and GS deviation signals, no inertial data, it can therefore not correct for the wind. It will initially ditch the wind correction angle, gets blown off LOC and then reinvent the wheel.

When guidance switches to PFCCs it will use inertial data to correct for the wind. Essentially, the A220 acts like a brand new FO everytime you enter approach mode, like “of there is the runway” and ditches the wind correction angle.

In real life, maximum deviation with a 20 kt crosswind at altitude is about 1/2 dot, with a 50 kt wind it will go almost a dot off. This initial “wobble” in real life has sorted itself out before DMC to PFCC hand-off (normally).