737 Anti Ice/CAT1

[ballyboley]

Quick question, we had a faulty cowl valve on the engine TAI, the engineers manually locked it on but it made the aircraft Cat1. Just wondering why the MEL/PDG restricted the aircraft to CAT1? I think there was something about a high stage valve being locked out as part of the rectification for the cowl valve.

Also as regards CAT1, our SOPs call for Gear down/F15 at glideslope alive on a CAT3 approach, however our normal approach would be low drag and gear down at 4-5nm. I've heard various reasons, but is there a technical reason why you cant do a low drag approach in a coupled CAT3?

Many thanks

[muduckace]

ballyboley

Also as regards CAT1, our SOPs call for Gear down/F15 at glideslope alive on a CAT3 approach, however our normal approach would be low drag and gear down at 4-5nm. I've heard various reasons, but is there a technical reason why you cant do a low drag approach in a coupled CAT3

Just about all equip. interperates loc/gs at higher sensitivities the closer you get to land/rollout. A high drag approach allows for better capture and loc/gs maintanance to avoid "no autoland" warnings or A/P disconnects. I believe reliability is the bottom line.