same approaches. Landing to the west at SAN, the best approach would be LOC 27 (localizer approach runway 27, has no glide slope, azimuth only). To the East it would be the ILS (like a localizer approach, but provides a glideslope too - most common instrument approach there is). Landing to the west you have issues with terrain and a parking garage under the flight path on the approach, not allowing enough clearance for an ILS approach, and the runway threshold is also displaced 2000ft down the runway, to provide the terrain clearance for the LOC27. Coming in over the water to RWY9, no terrain issues, but you have terrain issues in case of a missed approach. The required weather minimums for the LOC 27 are 1 3/4 miles visibility, and for the ILS 9 they are 1/2 mile visibility. The ILS 9 is considered a CAT1 approach. SAN uses RWY27 almost exclusively.

CATIII approaches have much lower minimums, the field equipment (ILS) has to be certified and more stringently maintained to certain specs (also, area near the touchdown zone needs to be “protected” from aircraft on the ground so as not to create an anomaly in the localizer or glide path signals, when CATII/CATIII operations are in effect). and the crews need to be trained and current to perform CATIII approaches - they are also required to use the autopilot to “autoland” and auto brakes are required as well during the rollout.

Generally, my visibility minimums are 300ft for CATIII, 1000ft for CATII (w/ autoland) 1200ft for (manual landing) and 1800ft or 1/2 mile for CATI (there are ex emotions to get lower mine in some CATI approaches using a HUD with EFVS - Enhanced Flight Vision System (think infrared or FLIR). Visibility for CATII/CATIII approaches are often reported as RVR, and are measured and required at 2-3 locations on the runway (touchdown zone, mid and rollout).

So, that is the short answer as to why you sometimes divert to LAX from SAN. I once diverted to Ontario from San Diego, with even better visibility than 1/2 miles - The ILS was out of service and I had to use an approach with higher mins requiring 3/4 miles visibility. I made extra money that day, and got home a day early too, with a first class ticket home. 😎👍🏻


[Post edited by B777Fr8Dog at 01/30/2020 5:05PM]