hi,i have a problem when descending on an ils path in autopilot. i approach the g/s, switch on the app-hold button in cmd-a mode. the ap engages and i descend along the g/s. at some point though for an unknown reason the app disengages and the plane levels off. i can't figure out how to manage a normal uninterupted ils approach. i did a series of ils approaches on the same airport just now. out of 4 attempts only 1 time did the ap lead the plane poperly, the other 3 times the ap lost the g/s and i had to land manually. i found a variety of old forum discussions but nothing helpful really. any help is appreciated.cheers

Just a couple of pointers but you may already have read about these.Firstly are you capturing the glideslope at the right time- I personally select APP once the localiser is established. I'm sure there will be others who do it differently but I have found this works for me. Also are you configured for landing- for example if you select a flap setting and reduce speed the aircraft will pitch nose up and may be above the glide path which will disengage the APP.It's all about getting the aircraft configured correctly. So to summarise speed/flaps/VOR/LOC/APP.I hope that helpsAlan W

Hi Stanley,What was you speed on the glide slope - and did you have the autothrottle on?I would then suggest to try and see if you have the same problem at different airports (try a runway with one ILS - ie no backcourse, just to be certain).Difficult to suggest anything else unless you provide more details on your config (OS) and - definitely - a screen copy.Also, some problems are corrected by using the Flight 1 registry repair tool (available on their site). At this stage it's almost like trying everything in the medecine chest without a full diagnosis by a doctor, but it certainly can't hurt your system !Hope this helps,Bruno

thanks, but i am already on the g/s descendeing nicely in app-hold mode when for an unknown reason the plane all of a sudden loses the g/s. this is the issue. speed and flaps are set, things are seemingly fine (at least that's what i think and that's what i do with any plane without problems) but then they aren't.mysterious.is it possible that the 737 only allows a very minor deviation from g/s to disengage app-hold? like for example adjustments to maintain on course in windy conditions? if so that plane would be very unique in that respect. the manual doesn't explain much either.cheersedit: approach speed 160, autothrottle on, and i have the same issue on other airports as well.

edit: approach speed 160, autothrottle on, and i have the same issue on other airports as well.

160 seems a bit high - especially with full flaps but should still be OK. What is your Vref ? And by the way, which version of the 737 is it and at what weight?Otherwise, as mentioned above, a screencopy would help.Bruno

Screenshot!!Bert Van Bulck

Unlike some planes, the 737 Mode Control Panel is what some refer to as a "wish list." It's what you want, not what it's doing. What indication are you getting from your Flight Mode Annunciator at the top of your Attitude display? Across the top it should read MCP SPD | LOC | GS with the autothrottle engaged or <blank> | LOC | GS without the A/T.That you are referring to "App Hold" makes me think that you're looking at the MCP "APP" light - which should not be illuminated once you're established. I'm going to guess that you're above the G/S the whole time, and the plane is just leveling off at your selected ALT.

hi,i have a problem when descending on an ils path in autopilot. i approach the g/s, switch on the app-hold button in cmd-a mode. the ap engages and i descend along the g/s. at some point though for an unknown reason the app disengages and the plane levels off. i can't figure out how to manage a normal uninterupted ils approach. i did a series of ils approaches on the same airport just now. out of 4 attempts only 1 time did the ap lead the plane poperly, the other 3 times the ap lost the g/s and i had to land manually. i found a variety of old forum discussions but nothing helpful really. any help is appreciated.cheers

You said you were in cmd-a mode. You need both autopilots to make an automatic approach so you need app + cmd A & cmd B

You said you were in cmd-a mode. You need both autopilots to make an automatic approach so you need app + cmd A & cmd B

You'd need both A/P to do an auto-land, but you can do a single-channel approach. Neither would seem to give the results described.

Hello Stanley, one thing you have not mentioned in your description of this fault, and I am assuming you have not done this, is whilst some 20 miles from airport click on INIT, top left in FMC and you will get your speeds for the ILS approach together with the ILS radio frequency. Hop this helps. richard welsh. PS- try signing your posts.

thanks guys,all replies combined made me make some adjustments in my latest tests and lately i haven't been missing any g/s. i suppose the main reasons for my problems were too high approach speed and too high g/s intercept altitude which the ap probably cannot compensate for. all in all the 737 seems to require being flown within smaller margins than other planes, but that's fine.thanks to all of you for assisting me sorting out my problem and making me learn new stuff :-)cheers, stanley

thanks guys,...and too high g/s intercept altitude which the ap probably cannot compensate for.

You're welcome.And don't forget you should ALWAYS intercept g/s from below. Never from above.Cheers,Bruno

You're welcome.And don't forget you should ALWAYS intercept g/s from below. Never from above.Cheers,Bruno

Most airlines these days ascribe to the Stabilized Approach Criteria. http://www.skybrary.aero/bookshelf/books/864.pdfI've been vectored many times high onto the approach, but as long as we meet the stabilized approach criteria, I haven't gone around. I've only gotten one false G/S in 20+ years.

Most airlines these days ascribe to the Stabilized Approach Criteria. http://www.skybrary....f/books/864.pdfI've been vectored many times high onto the approach, but as long as we meet the stabilized approach criteria, I haven't gone around. I've only gotten one false G/S in 20+ years.

Thanks,I guess then : "It is always preferable to intercept g/s from below." would be more correct, right? (In real life, I only fly ultralight planes - ie always VFR and no ILS)Bruno PS : That skybrary is really great !

Thanks,I guess then : "It is always preferable to intercept g/s from below." would be more correct, right? (In real life, I only fly ultralight planes - ie always VFR and no ILS)Bruno PS : That skybrary is really great !

The "intercept a G/S from below" is a great FAA written answer, but in practice, it often doesn't work that way. If you're 10-15 miles out and high on the approach, it's not uncommon. I certainly wouldn't go-around for that. Just make sure you get down and are stabilized.