Hello, just landed at glasgow useing a loaded flight plan everything was perfect... when on finals i clicked the app button entered the landing speed of 151 and 30flaps then pressed CMD B it landed perfectly but i could not see land 3 anywhere?what did i do wrong and if so why would it then do a perfect auto landing?many thanksjames.

Hello, just landed at glasgow useing a loaded flight plan everything was perfect... when on finals i clicked the app button entered the landing speed of 151 and 30flaps then pressed CMD B it landed perfectly but i could not see land 3 anywhere?what did i do wrong and if so why would it then do a perfect auto landing?many thanksjames.

It would announce CMD instead of Land 3 with Fail Passive ! Were you using the Honeywell MCP ?

Thanks Frederic, i used what ever was default in the FMC and not changed anything,and yes it did say CMD.and what does CMD stand for? new boyjames

Thanks Frederic, i used what ever was default in the FMC and not changed anything,and yes it did say CMD.and what does CMD stand for?new boyjames

CMD is just the standard autopilot engaged annunciation.You will see it when you engage an autopilot after takeoff.

CMD means COMMAND. As Frederic told you is te common annunciation for AP engagement, with exception of the landing phase.When on landing (APP pushed and no light) CMD indicates that both autopilots are working togheter to land the plane. Another annunciation will be a white FLARE displayed. If 1CH appears means that a single autopilot is used to approach, no autoland is permitted, also if the AP alone is still capable of doing.

this is something I don't quite get. Theoretically could the plane still land itself with only single channel available? Let's think of the following scenario: crew tunes only one nav radio to the ILS frequency, captures localizer followed by glideslope with the autopilot engaged (CMD). And instead of disengaging/disarming the autopilot and autothrottle before minimums, leaves them on all the way to touchdown. Will the autopilot flare, touchdown, and maintain rwy centerline in such a scenario or would it simply fly the acft into the rwy? And why is there a difference in annunciation in the FMA between acft that have fail-operational and fail-passive systems? I did look this up in the manual but could not find it. thx for the help

Thanks,what is the difference between CMD A, AND CMD B ,i had the CMD A on straight after take off PLUS LNAV AND VNAV on finals when steady i pressed APP then CMD B,the APP light then went out along with LNAV and VNAV, armed speedbrakes and then made a perfect landing..(both NAVS tuned in) many thanks andrea, james

Think CMD A and, CMD B is Dual autopilot for safety, meaning you activate 2 autopilots ;)

On classics the flare function is only made with both AP in dual channel (both working, both selfmonitoring and watching what the other does, both with a different and not interconnected power source as when dual will become active, the TR3 will be disconnected) so with a single channel the plane will not flare.On NGs the things are a bit different, the flare function is coded inside each FCC and only one is able to do it.I must check on my manuals if the second one must be active (also if not engaged) with the radio tuned for cross check of functions, but I'm pretty sure you cannot autoland with only one ILS tuned. It is too dangerous to let a single system to manage such a delicate phase of flight. One AP is sufficient, is capable, and by visually checking the operation, pilots sould let the AP to do the job (not legally permitted), but with a single source of information (one ILS tuned) I don't think it is good for operation. An onboard system can break or could give wrong informations, while with 2 systems you can check. Without a second ILS tuned pilots will not ave any oter source of info about how the only tuned ils is working.

737 has 2 autopilots, during normal operation one autopilot is active, the other is monitoring the first one.CMD A and B and CWS A and B activates the relative flight control computer FCC (A or :(.For the flight you can engage wichever you want or the one is still working (if you have one failed)When on landing, to have better accuracy and less possibility to have wrong data or computation, the 2 autopilots works together to land te plane correctly. Both are working, both are monitoring.During flight, you have 2 FD switches, near tese switces there is a MA ligt, this light tells the pilot wich FCC is the master, the one that moves the symbols on the PFD. During landing or TOGA both becomes master a they are working independently.

Thx for the reply Andreas. That's what I thought. It would be interesting to have some of our friends who do this for a living experiment on their level-D sims when they get the chance and are not undergoing actual exams/checks

Also, it's important to see the difference between the 'fail passive' and 'fail operational' systems. 'fail passive' simply means that a single failure will require the pilot to take over the landing, whereas 'fail operational' means that autoland can continue with a single failure. In fact, a single failure in a 'fail operational' system causes it to revert to 'fail passive' (the next failure will require the pilot to take over). LAND 3 and 'rollout' is only displayed for fail operational autoland. On the PMDG NGX, I believe you have to set fail passive/fail operational independently of Honeywell/Collins MCP. That is, to get LAND 3 you need to have the Collins MCP and also have fail operational autoland enabled- which I think just happens when you have the electronic standby instrumentation. You can tell by looking at the lower DU selector (which has the ENG and SYS buttons). If there are only 2 buttons, you have fail passive. If there are 3, then it is fail operational.

Thanks for the info ;) , my knowledge is limited to HW A/P.

Also, it's important to see the difference between the 'fail passive' and 'fail operational' systems. 'fail passive' simply means that a single failure will require the pilot to take over the landing, whereas 'fail operational' means that autoland can continue with a single failure. In fact, a single failure in a 'fail operational' system causes it to revert to 'fail passive' (the next failure will require the pilot to take over). LAND 3 and 'rollout' is only displayed for fail operational autoland. On the PMDG NGX, I believe you have to set fail passive/fail operational independently of Honeywell/Collins MCP. That is, to get LAND 3 you need to have the Collins MCP and also have fail operational autoland enabled- which I think just happens when you have the electronic standby instrumentation. You can tell by looking at the lower DU selector (which has the ENG and SYS buttons). If there are only 2 buttons, you have fail passive. If there are 3, then it is fail operational.

What determines which Honeywell/Collins MCP you have in your plane? Is it certain liverys only use 1 of the mcp's? For instance I have only used the default pmdg 738 and the AA 738, the latter having only 2 buttons on the DU selector. So the 2 button DU aircraft wont allow LAND 3 then? THANKS!!

On NGs the things are a bit different, the flare function is coded inside each FCC and only one is able to do it.[...]One AP is sufficient, is capable, and by visually checking the operation, pilots sould let the AP to do the job (not legally permitted), but with a single source of information (one ILS tuned) I don't think it is good for operation.

Are you saying the flare could be performed with only one AP engaged? Without a specific failure scenario, this is yet not possible to set up manually, is it?

On the PMDG NGX, I believe you have to set fail passive/fail operational independently of Honeywell/Collins MCP. That is, to get LAND 3 you need to have the Collins MCP and also have fail operational autoland enabled- which I think just happens when you have the electronic standby instrumentation. You can tell by looking at the lower DU selector (which has the ENG and SYS buttons). If there are only 2 buttons, you have fail passive. If there are 3, then it is fail operational.

Actually there is some dependancy. While you can have Collins MCP and ISFD, that doesn't make you fail-op. Those are however requirements, but the fail-op is a seperate switch. In any case if you activate fail-op you'll get the Collins and the ISFD automatically.

What determines which Honeywell/Collins MCP you have in your plane? Is it certain liverys only use 1 of the mcp's? For instance I have only used the default pmdg 738 and the AA 738, the latter having only 2 buttons on the DU selector. So the 2 button DU aircraft wont allow LAND 3 then? THANKS!!

Well, you can set this up on a per-livery basis. Some have their real world specs included, others don't. And yes, if you lack the C/R button you're fail-passive, regardless of your MCP and standby instrumentation. However if you want to be fail-op, minimum requirement is Collins MCP and ISFD, as stated above.