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"SINGLE CH" During Dual Channel Approach

Featured Replies

I agree with you regarding capturing the localiser in APP mode (FCOMv2 4.10.15) Do you have any reference to show what happens using VOR/LOC mode? Doug
There is no reference in the Boeing FCOM Vol 2 about CMD being annunciated for localizer capture in VOR/LOC modebecause it is just a standard AFDS mode and CMD is annunciated anyway.It would be helpful if Boeing did little things like this but they don't.Their FCOM's can even be a bit misleading sometimes. Fred.
so when is the appropriate time to engage the other AP, or in most cases CMD B? A lot of the time, for me anyway, I have a hard time getting both A and B to stay connected at the same time. Thanks!
Just after you have captured the localizer and glideslope in APP mode !! Fred.

Frederic Steiner.

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  • Author
so when is the appropriate time to engage the other AP, or in most cases CMD B? A lot of the time, for me anyway, I have a hard time getting both A and B to stay connected at the same time. Thanks!
You can only select the second AP after selecting APP mode. If you select the other AP before this they merely swop over. Fred states that most airlines use APP mode for localiser capture which will then go on to capture the glideslope. I believe this is normal in the States for example, but I could be wrong. The problem with this is that you can capture the glideslope before the localiser which may result in you following a false glideslope. And technically you should not start down the glideslope until cleared by ATC. Some countries have regulations prohibiting glideslope capture prior to localiser capture (to avoid false glideslopes) in which case VOR/LOC is used to capture the localiser. Once cleared for an ILS approach you can select APP in order to capture the glideslope, then select the second AP. Cheers, Doug

Doug Boynton

  • Author
There is no reference in the Boeing FCOM Vol 2 about CMD being annunciated for localizer capture in VOR/LOC modebecause it is just a standard AFDS mode and CMD is annunciated anyway.It would be helpful if Boeing did little things like this but they don't.Their FCOM's can even be a bit misleading sometimes. Fred.
Yes indeed. Have you noticed how less & less information is provided as time goes by? Doug

Doug Boynton

Yes indeed. Have you noticed how less & less information is provided as time goes by? Doug
I sure have Doug !That is why the Boeing CBT is so popular with guys training etc.It is much more intuitive for learning. ( The AoA training videos will be the way to go for anyone who really wants to learn this aircraft !!) Fred.

Frederic Steiner.

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  • Author
I sure have Doug !That is why the Boeing CBT is so popular with guys training etc.It is much more intuitive for learning. Fred.
I'd be interested in seeing that; where can I get a copy & how much is it? Doug

Doug Boynton

I'd be interested in seeing that; where can I get a copy & how much is it? Doug
The Boeing CBT (Computer Based Training) is not available as far as I know to the general public.I got my copy of it when I flew for Ryanair. It is very good and makes learning so much easier.I have no idea how much it actually costs. I was chatting with Chris from AoA and he told me that their videos will be even better.I am inclined to believe him as I have seen some of their stuff and it is excellent. Fred.

Frederic Steiner.

B7382.jpg

  • Author
The Boeing CBT (Computer Based Training) is not available as far as I know to the general public.I got my copy of it when I flew for Ryanair. It is very good and makes learning so much easier.I have no idea how much it actually costs. I was chatting with Chris from AoA and he told me that their videos will be even better.I am inclined to believe him as I have seen some of their stuff and it is excellent. Fred.
Thanks for the info. It looks like the AoA product for the NGX is still under development, I will stay tuned... Doug

Doug Boynton

People are still having a problem understanding this !!! If you capture the localizer with VOR/LOC it will announce CMD.( you cannot have single channel in VOR/LOC mode !!!)If you capture the localizer with APP it will announce Single Channel.it will be Single Channel untill 1500 feet and then change to Land 3 for the Collind MCP or back to CMD for the Honeywell MCP.( provided you have also captured the glideslope of course.) This is correct and has been correct since Hotfix 3.Before hotfix 3 it was not correct. Fred.
I thought it was the selection of backup instruments that determined whether it shows "land 3", or "CMD".. ??IE: you have to have the newer backup instrument todo land 3, or I was thinking anyway.. I was thinking eithertype of MCP could do both if you had the proper backupinstrument installed. But, maybe I'm missing something, andyou need both. ?Myself, I use the older classic backup instruments, so Inever see "land 3".. But I am using the Collins MCP.

Mark Keith

I thought it was the selection of backup instruments thatdetermined whether it shows "land 3", or "CMD".. ??IE: you have to have the newer backup instrument todo land 3, or I was thinking anyway.. I was thinking eithertype of MCP could do both if you had the proper backupinstrument installed. But, maybe I'm missing something, andyou need both. ?Myself, I use the older classic backup instruments, so Inever see "land 3".. But I am using the Collins MCP.
The Collins MCP needs the ISFD for Fail Operational to work.If you use the classic backup instruments (analog) it will only give you Fail Passive. The Hoeneywell MCP is Fail Passive only. Either way you can autoland the plane but without Rollout.You must steer the plane after touchdown. Fred.

Frederic Steiner.

B7382.jpg

OK. I was thinking either MCP could do fail operational as long as you had the ISFD.But, guess not..

Mark Keith

OK. I was thinking either MCP could do fail operational as long as you had the ISFD.But, guess not..
No !! Just the Collins.It has a third channel for full autopilot Rollout. Fred.

Frederic Steiner.

B7382.jpg

OK. I was thinking either MCP could do fail operational as long as you had the ISFD.But, guess not..
Nope. ISFD is a requirement, as is the Collins MCP. Those alone still don't make you fail-op. sig.gif
  • 2 years later...

you have to understand first that there is 2 autopilots command CMD A and CMD B  ,each one is considered as a channel so how this work in approach procedures ?

we assume that you have set both ILS frequencies and courses and you are not below 1500 feet RA and about 30 degree intercept   heading  ;now push the  approach button on MCP,than push CMD B now   you will see both VOR/LOC and G/S are armed on FMA (flight mode annunciator) until now the AFDS shows CMD in green.When the LOC is captured FMA shows VOR/LOC in green   and the AFDS switches from CMD to SINGLE CH this tell you that only one autopilot is engaged until now .When both VOR/LOC and G/S are engaged SINGLE CH will switch to CMD again when airplane reaches an altitude below 1500 RA this tell  you that the second autopilot is engaged now you can see also that FLARE mode is armed which will engage at 50 RA approximately.

 

let me know if you have other question;

have a good flight.

 

All good. And at 400ft ish you should hear a good long stab trim up sound from the autopilot as it preloads the controls for the flare manouver. Bit weird but normal.

Mark Harris.

Aged 54. 

P3D,  & DCS mostly. DofReality P6 platform partially customised and waiting for parts. Brunner CLS-E Yoke and Pedals. Winwing HOTAS and Cougar MFDS.

Scan 3XS Laptop i9-9900K 3.6ghz, 64GB DDR4, RTX2080.

B737NG Pilot. Ex Q400, BAe146, ATP and Flying Instructor in the dim and distant past! SEP renewed and back at the coal face flying folk on the much deserved holidays!

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