Cat IIIb Autopilot Disconnect
 

Perhaps some of the pilots on this forum could help out a techie with an operational query?! I'm currently looking at Cat IIIb performance requirements for a potential future generation of landing systems.

I am interested in knowing at what point on a Cat IIIb landing do you disconnect the autopilot? Is it as soon as you get the main gear on the ground or do you keep it locked in through roll out until the aircraft has slowed enough for you to safely use visual cues to keep the aircraft on the runway?

Also, once you have disconnected the autopilot do you still use the localiser to keep you on the runway until you find the exit taxiway?

TIA

FK 100 - Disconnect @ 60kts and if necessary stop on the runway until a follow me arrives or directions given by GMR. If taxiing clear then localiser centre line guidance may be used (manually) until a taxiway can be identified. ;)

A/P remains engaged through roll-out until able to safely visually taxi.

Airbus A320/1

Autopilot could remain engaged down to stop.
Usually disconnected when Cat2/3 turnoff (amber/green)lights identified.
'Yaw Director'on PFD continues to give centreline guidance-symbol driven by localiser sygnal.

Airbus A340 - same as A320/1 given above. Genrally we disconnect when slow enough to see what the hell's happening outside :) but A/P will remain engaged until the aircraft longitudinal axis diverges from the runway centreline by 20 degrees (I think - may be 30) ie. you can start turning off with the A/P engaged (NWS overriding A/P).

The yaw bar at the bottom of the PFD will give you centreline guidance if you need it - much easier to let the aeroplane do it till you can assimilate what's going on outside!!

Many thanks to all for replying. Looks like I have my answer! :)

The main difference between CAT111b, and CAT11 and CAT111a, is that in order to fly a 111b approach you need a fail operational autopilot. You also need automatic roll out.
This may be modified by HUD and or PVD, which for some authorities, will allow you to use a DH below 50ft, but not down to a 0 DH and 75m