This is a constantly recurring problem for me, which I have yet been unable to solve.
I am on approach for an ILS landing in the 737. I am 35 miles or so out, at 8000 ft, on runway heading, with the ILS frequency for the runway tuned to Nav 1. I am on AP with HDG, SPD and ALT activated.
At 27 miles out, the localizer activates. I hit NAV on the AP and the plane begins to seek (and finds) the localizer. At 23 miles out, I begin a descent to 1200 ft AGL. Early in the descent, the glide slope indicator (GSI) activates. When it does, I hit APP on the AP.
As I continue the descent to 1200 feet, all of a sudden and for no apparent reason, the ALT hold on AP deactivates. The ALT light just goes out and the plane begins to immediately lose altitude from its descent path. I have to click on ALT to reactivate it and get the plane back, on the proper descent path.
That's the first part of the problem. The second part takes place when the plane reaches the glide slope. I will have been level at 1200 ft. for a short period of time. The GSI karat begins to come down as the plane approaches the glide slope. I am "flying into" the glide slope from underneath, as I am supposed to be doing.
When the karat reaches the midpoint on the GSI, the plane is supposed to begin down the glide slope - only it doesn't. It just keeps flying level. If I want to land it, I have to switch of AP and do it manually.
That's not my idea of an ILS/GS landing.
And, to further complicate matters, it doesn't happen all the time. I can have it happen, reset the flight, do it again, and it works fine. Then it won't. Then it will. GRRRRRRR!!!!!
When I tried to discuss this problem before, all I got was a huge chorus of "I don't have that problem - what are you talking about?" Well, I have this problem, and it's driving me nuts.
If you don't have this problem, don't respond to this thread - unless you used to have the problem and fixed it. Then I would like to know how you fixed it, of course.
So - any thoughts from anyone who might have experienced this issue?