It's fog season again around my local airport MUC (EDDM), and I have noticed a number of diversions recently. Some planes were holding a bit before attempting to land, performed a go around and then diverted to some of the nearby airports.
It appears that mostly smaller planes (< 200 seats) from not-so-distant departure airports diverted and most long-haul flights made it to the terminal as scheduled, maybe with a bit of delay.
This made me wonder what the specific reasons for the diversions could have been, and I am asking mainly for answers providing some of the top reasons, including the background information.
The airport allows for ILS CAT III approaches, which, in the case of CAT III C, translates to auto-land, possible even in no-visibility conditions, if I understand the details correctly.
This, depending on the equipment installed on the aircraft, would mean that planes capable of performing CAT III b or CAT III c approaches could land when the runway becomes visible 75 ft above ground, and all others couldn't? Would long-haul aircraft mostly be equipped with auto-land, while regional jets probably wouldn't?
Would ATC have to use bigger separation, reducing the airport's capacity, and it would be the smaller planes who lose the game of who-gets-chosen? This would, however, most likely not explain the above example of a flight actually trying the approach and diverting only after having done so?
Those who are familiar with the particular airport might be aware that there's a long debate going on about whether or not a third runway should be built. In what ways would (or wouldn't) a third runway help prevent diversions on foggy days? My guess is that CAT II planes would have to divert no matter how many runways were built, but maybe separation issues (in the air/on the ground) would be less of a trouble?