I agree with you all about being heads down on late final ! I know that some boeing autopilot flight director systems allow the flight crew to make a late runway change without disengaging the autopilot. You can transition to a new runway assignment if radio altitude is greater than 1500 feet. The system logic determines whether or not localizer and/or glideslope have been captured and enters predetermined modes as a result - therefore one can transition to the new approach while enabling instrument landing system retuning while maintaining autopilot engagement. I believe the modes are:
A) in the event localizer but not glideslope of the initial ILS has been captured,
i) maintain the aircraft's current pitch mode,
ii) disarm glideslope capture,
iii) transition aircraft roll to a predetermined roll mode, and
iv) enable ILS tuning to the desired runway,
B) in the event glideslope but not localizer of the initial ILS has been captured,
i) retain the current roll mode,
ii) disarm localizer capture,
iii) transition aircraft pitch to a predetermined pitch mode, and
iv) enable ILS tuning to the desired runway,
C) in the event both localizer and glideslope have been captured,
i) transition aircraft roll to a predetermined roll mode,
ii) transition aircraft pitch to a predetermined pitch mode and
iii) enable ILS tuning to the desired runway.
It will NOT work below 1500 - I really agree with your comment though " Just take the AP/FD off and fly the aeroplane! Assuming you are sidestepping to a parallel runway - you'll even get GS mini" Too expensive to go around .."- if you're too low for all that and IMC - go around "
Thanks ! Im familiarizing myself with the training philosophies between birds - Thanks !