Rainboe, I think the reason for "capture from below" is to avoid capturing a false glideslope, read any ATP theory book for all you can eat on the subject.
Everyone seems to have their own ideas, but I´m sure there was a chain of events which caused this, not some singular cause.
Being Number 3 behind the aircraft in question on the ILS for 18R that day I can offer some insight regarding weather conditions
Cloud base could have been a factor, but unlikely given it was OVC/800´ I believe.
Visibility: was around the 4000m mark, with a TEMPO of 2500m, so again, possible factor but unlikely.
Icing: We had Engine and Airframe Anti-Ice ON, as we were in cloud for some time, however we had no signs of ice, either through the ice detect system or any visible icing whatsoever, and the temperature remained positive throughout our IMC approach and GA.
Winshear: Again at circa 1500´ it was on the nose at 20 knots, and reporting 210/10 on the ground, so hardly windshear territory I´m sure we can agree, again not ruling anything out, but unlikely.
I´m sure a multitude of factors came into play, and while the weather wasn´t BAD, it was murky with no distinct horizon, I could hazard a guess with other events going on inside the flightdeck, the weather wouldn´t be helping.
Regards
Atreyu
