Question regarding GS interception when approach mode armed

[WhySoTough]

So your FAF, where the GS starts to come alive and you descend with the glide is for example 2000 feet.
If you were at 4000 feet with your approach mode armed, I believe it will intercept the localizer, but will it also descend down to your FAF and further with the glide, or do you have to descend to 2000 feet for the GS to become active and descend with the glide?

Also, is there a certain altitude with your approach mode armed for the localizer to start intercepting?

Thanks!

[CAT3C AUTOLAND]

On the Airbus, the aircraft will not intercept the G/S without being bolted to the localizer. In terms of where it intercepts is based on where the aircraft is in space.

For example in the aircraft is 2000ft AGL at 10 miles, it will track the LOC until it gets to just over 6 miles (assuming a 3 degree glide 318ft per mile) and the aircraft will descend down the G/S provided it is armed. However, if the aircraft is at 4000ft AGL and the aircraft is just over 12 miles, again assuming a 3 degree glide, as long as the aircraft displaced correctly vertically, and the glide slope is armed the aircraft will descend on the glide slope. It wont wait until the FAP. Remember a FAF is associated with non precision approaches :ok:.

Hope that helps.

[Tinribs]

This post highlights a problem which has not been published clearly accross the types. Each conversion I did concentrated on the type concerned and not on the ways in which it was different to the previous type flown of others within the same range.

This problem helped to cause the Kegworth crash when we might have thought smoke in the flight deck after an engine failure suggested a particular engine at fault when the 737 400 system was slightly different to the 300 negating this idea

Advice on this thread has related to the airbus of which I am highly ignorant. I flew the sim for a few minutes on several occasions for the experience but not enough to gain any expertise

On the 737 300/400/500 if approach was selected on catching the glide path the aircraft would descend with it irespective of localiser situation. Something to do with curved approaches used in other countries

Once selected some very fast switching was needed to get out of approach, it could be done but usually wasn't

So beware of thinking the rules for one aircraft type relate to others, the logic may be the same but the engineering solution may be different

I remember my instructor, Dick Felix, wacking the back of my bone dome with something solid at Oakington when I descended on the glideslope without first sufficiently collecting the localiser. Good training, I never did it again