Wondering why both your AutoPilots do not work on approach?

[Paul Deemer 13]

If any of your were wondering what the answer to this question is. Here is what I found out through trial and error, and also looking through the Manuals. Captain and First Officers FD's must be ON.Captain and First Officers ILS Course must be set on MCP.Captain and First Officers Nav Radios must be set to ILS Frequency.And finally you need 2 Power sources for both AutoPilots to work. If you have AC Power set to Generator 1, Generator 2, or APU Generator only then you are only using 1 source of power and both Autopilots will not engage at the same time. Set AC power to standby then you will have 2 AC Power sources available. As for DC power leave that in the Battery Power Position for all phases of flight. You can't do a Full Autoland with only 1 Autopilot. I also think I read something in the FCC Regulations that prohibits trying to Autoland with only 1 AutoPilot. So make sure all of the above are set before you try an Autoland. Worked fine once I figured that all out. The 737-NGX is not like the bigger Boeings like the 747-400 where you can just hit approach and all 3 Autopilots engage automatically. If I missed anything or made and error feel free to correct me. Just going by my last flight and all the variables I had to use to finally get both AutoPilots to work at the same time on ILS.

[gtjoha 0]

Helpful! Thanks a lot :)

[WTE_Pharoah 7]

wow thanks for that...I tried switching on the autoland and nothing....now I know why.

[Mats_J 1]

And finally you need 2 Power sources for both AutoPilots to work. If you have AC Power set to Generator 1, Generator 2, or APU Generator only then you are only using 1 source of power and both Autopilots will not engage at the same time. Set AC power to standby then you will have 2 AC Power sources available. As for DC power leave that in the Battery Power Position for all phases of flight.

Paul, Are you talking about the electrical display on the overhead here? If so the selectors have nothing to do with how many, or what sources are available. Just what is displayed on the panel. Unless you have failure and/or disconnected the ENG GEN those are your two main AC sources. (And the APU as backup third source.) The bus tie will transfer as it senses lack of AC power on either bus. Short and dirty. Hope it helps,

[Paul Deemer 13]

Paul, Are you talking about the electrical display on the overhead here? If so the selectors have nothing to do with how many, or what sources are available. Just what is displayed on the panel. Unless you have failure and/or disconnected the ENG GEN those are your two main AC sources. (And the APU as backup third source.) The bus tie will transfer as it senses lack of AC power on either bus. Short and dirty.

Your right, I posted this way back during release week when I didn't know what I was talking about lol. For Clarification and to avoid Confusion just follow below.

Captain and First Officers FD's must be ON.Captain and First Officers ILS Course must be set on MCP.Captain and First Officers Nav Radios must be set to ILS Frequency.

Forget the part about power sources (DC is usually in Battery Position and AC in Gen1 or Gen2 position).

[Spin737 102]

And finally you need 2 Power sources for both AutoPilots to work. If you have AC Power set to Generator 1, Generator 2, or APU Generator only then you are only using 1 source of power and both Autopilots will not engage at the same time. Set AC power to standby then you will have 2 AC Power sources available. As for DC power leave that in the Battery Power Position for all phases of flight.

Don't monkey with any of that stuff unless a QRH procedure tells you too! If you had an IDG fail, you could use the APU as a power source for an autoland.

Actually I forgot about this thread and the above is not accurate. Usuaully now on approach I have DC Power set to Battery and AC Power set to Generator 1.

Wait, Generator set to 1? Just have GENs 1 & 2 online like always and you should be good to go.

[Paul Deemer 13]

I don't think we are talking about the same thing. Your talking about having both Generator 1 and 2 flip switches set so that both Generators are online. I am talking about the Position of the Switch knobs at the Top. I inncorrectly stated that they should both be in the standby power position but actually the manual says Battery Position for DC Power and Generator 1 or Generator 2 for AC power.

[JRBarrett 1,336]

I don't think we are talking about the same thing. Your talking about having both Generator 1 and 2 flip switches set so that both Generators are online. I am talking about the Position of the Switch knobs at the Top. I inncorrectly stated that they should both be in the standby power position but actually the manual says Battery Position for DC Power and Generator 1 or Generator 2 for AC power.

If the rotary knobs are the ones I think you are referring to, they select which power source(s) will be displayed on the digital indicators of the AC & DC power monitoring panel. (AC or DC voltage, current draw, and in the case of the AC sources, the frequency). The position of the rotary knobs has no effect on which power source is actually used by any aircraft system.

[Paul Deemer 13]

If the rotary knobs are the ones I think you are referring to, they select which power source(s) will be displayed on the digital indicators of the AC & DC power monitoring panel. (AC or DC voltage, current draw, and in the case of the AC sources, the frequency).

First to admit when I am wrong or didnt know what I was talking about. What got me confused was reading some other website about power requirements and autoland and I thought those Rotary Knobs had something to do with selecting the 2 power sources but yeah I understand what they do now. It does say 2 power sources have to be available for both AutoPilots to Work but the knobs have nothing to do with which power source is being used, which is where I made a mistake.

[JS212 4]

Thank you for that tip! It worked perfectly. I was about to ask that question on the forum.

[JRBarrett 1,336]

First to admit when I am wrong or didnt know what I was talking about. What got my confused was reading some other website about power requirements and autoland and I thought those Rotary Knobs had something to do with selecting the 2 power sources but yeah I understand what they do now. It does say 2 power sources have to be available for both AutoPilots to Work but the knobs have nothing to do with which power source is being used, which is where I made a mistake.

It would probably be good practice before commencing a CAT III approach to use those rotary knobs to check the actual voltage/current/frequency readings for the various AC sources, (normally GEN 1, GEN 2 and STBY in-flight). Even though there may not be any obvious failure indications (like a generator tripping off-line), if you have failures enabled in the sim, the first sign of a source going "sour" might be seen on the digital readouts. i.e. voltage going well below (or above) 115 volts, or frequency drifting excessively. (Should always be within a few cycles of 400 Hz +/-)

[henri5 16]

Another reason that happened to me today in flight from San Diego to LAX is that I forgot to program the approach page (flaps and speed) when it became available. As a result, the FMC kept telling me to program the speed on the MCP (which apparently does not come available until you have done the latter), and my plane floated over the runway and went to do the go-around routine, despite my attempts to force it to land. I went around and landed by hand. Since I had autolanded a number of times before, I figured I should try again, and this tie I did everything correctly. When the time came, I pressed the localizer button when lined up with the airport, and when the glideslope was grabbed, turned on the second autopilot for a perfect CAT3 landing. And don't forget to put the runway altitude in the pedestal. Henri

[RYR738 8]

If any of your were wondering what the answer to this question is. Here is what I found out through trial and error, and also looking through the Manuals. Captain and First Officers FD's must be ON.Captain and First Officers ILS Course must be set on MCP.Captain and First Officers Nav Radios must be set to ILS Frequency.And finally you need 2 Power sources for both AutoPilots to work. If you have AC Power set to Generator 1, Generator 2, or APU Generator only then you are only using 1 source of power and both Autopilots will not engage at the same time. Set AC power to standby then you will have 2 AC Power sources available. As for DC power leave that in the Battery Power Position for all phases of flight. You can't do a Full Autoland with only 1 Autopilot. I also think I read something in the FCC Regulations that prohibits trying to Autoland with only 1 AutoPilot. So make sure all of the above are set before you try an Autoland. Worked fine once I figured that all out. The 737-NGX is not like the bigger Boeings like the 747-400 where you can just hit approach and all 3 Autopilots engage automatically. If I missed anything or made and error feel free to correct me. Just going by my last flight and all the variables I had to use to finally get both AutoPilots to work at the same time on ILS.

Just to add to that !! You can't engage both autopilots untill you have selected APP first !! The autopilot status should be " Single Channel " until you descend below 1500 feetthen it will change to " Land 3 " and Rollout and Flare will be armed and annunciated in white on the PFD. The autopilot has to be manually disengaged after touchdown. Fred.