Question 1 answer only:
The minimum temperature advise you of the temperature at which sufficient ground clearance for the procedure is maintained. Hence different airports use different temperatures, due obstacles in the approach path segment.
Correcting the FMC altitudes for cold weather depends on the approach type being flown:
- LNAV approaches do require cold weather corrections to be made;
- LNAV/VNAV approaches do not require cold weather correction from the FAF inbound (safeguarded by minimum use temperature), but do require cold weather corrections to be made prior to the final approach segment; this is as the final approach segment in LNAV/VNAV is a managed approach angle by procedure design.
- APV approaches also do not require any cold weather corrections to be made from FAF inbound due procedure design.
The DA however should
always be set with the applicable cold weather correction applied. The DA is not connected to the FMS in this sense and indicates the aircraft altitude sensed in cold weather thus will under-read height above ground. Not applying the cold weather correction will get you lower than allowed at minimums, not setting it thus would allow a pilot to descend below procedure minima, a wrong operational technique to get below the reported cloud base.