Glide Slope Disconnecting

[pangaul 0]

Hi all,Can anyone please help, my problem is that when I capture the glide slope from underneath at correct speed, flaps etc, as soon as the aircraft is locked on and tracking the GS, it drops out and the green app light go’s out on the MCP and will not reactivate. I have to fly the approach manually, this is not a problem in its self but this dropping out can’t be right. I have searched this forum and have read all the posts on glide slope issues but can’t find an answer to my problem. All my instruments are set correctly as far as I am aware. I have ‘GS on’ selected in the FMC, the correct nav frequencies are selected, I have no problems capturing the localiser. Also I have the correct runway listed in the routes page under departure / arrivals, I even have the runway elevation set on the overhead. So have I got something wrong or is this a problem that will be sorted out with service pack 1. I do not have this problem when flying the ifly 737ngx. This happens on different approaches and is not subject to a single airport. Many thanks for any help received.Paul Breeze

[emvaos 13]

First GS is an AFS mode not an FMC mode so what you have entered in related pages does not really matter (except for GS ON/OFF).The green APP light goes out on the MCP when you capture the glideslope (GS) or the glidepath (GP). In 737-speak it means you cannot deselect this mode any longer by pressing the button. Same as ALT HOLD at MCP altitude and a few other modes associated with, for example, TOGA.

[William J.S.S 173]

Also make sure you have your second autopilot button green.....

[Flamin_Squirrel 71]

Also make sure you have your second autopilot button green.....

Not a requirement for the autopilot to maintain GS.

[Spin737 102]

Hi all,Can anyone please help, my problem is that when I capture the glide slope from underneath at correct speed, flaps etc, as soon as the aircraft is locked on and tracking the GS, it drops out and the green app light go’s out on the MCP and will not reactivate. I have to fly the approach manually, this is not a problem in its self but this dropping out can’t be right. I have searched this forum and have read all the posts on glide slope issues but can’t find an answer to my problem. All my instruments are set correctly as far as I am aware. I have ‘GS on’ selected in the FMC, the correct nav frequencies are selected, I have no problems capturing the localiser. Also I have the correct runway listed in the routes page under departure / arrivals, I even have the runway elevation set on the overhead. So have I got something wrong or is this a problem that will be sorted out with service pack 1. I do not have this problem when flying the ifly 737ngx. This happens on different approaches and is not subject to a single airport. Many thanks for any help received.Paul Breeze

Ops check normal. Returned to service. The green light on the MCP should go out. Look at your FMA to see what's happening, not the MCP. If you have loc and gs on the FMA, then you're all set. And no, there is no need for a second autopilot or a first autopilot, for that matter.

[William J.S.S 173]

Sorry, I think now that I must have misunderstood the OP......

[markadeane 272]

Matt has got it right: In all cases you should refer to the Flight Mode Annunciator at the top of your PFD for info on what modes are active/armed. Relying on the button lights on the MCP can be misleading.

[pangaul 0]

Thanks guys,taken on board what you've said, I will give it a shot now and review an ILS approach into EGKK Gatwick UK, one of my favorite airports and will report back my findings.Paul Breeze UK

[pangaul 0]

Back from my short test flight.All went well, it would appear that because the green light went out I assumed the glide path had disconnected and as such it didn’t occur to me to check the FMA, so I automatically disconected the AP and flew manually. Following your advice I watched the GS capture on the PFD and confirmed it by the green annunciator and allowed the aircraft to follow a perfect approach.Many thanks guys Paul Breeze

[Tabs 2,790]

MCP button lights aren't mode indicators - as others said, look at the FMA for that. If you see VOR/LOC | G/S you're still good. When the MCP button lights go out on an approach it's telling you that you are locked into your current modes and can't disengage them other than by pressing TO/GA to go around. The same thing happens during takeoff too after you press TO/GA.