How come you got 'STD' set on your altimeter at 1920 feet? And also your gear is down! You should also have a pitch and a roll mode activated on your MCP, preferably VNAV and LNAV, before engaging the A/P

Best I can tell your Flight Director is off. I'm not an expert on the 737 systems, but you might want to try turning both flight directors on, then select a mode, then engage an autopilot.

Hi Tom,Like Fred said, aircraft not configered for take-off. Gear still down,vors not turned on,flight directer off,heading bug not set on heading, speed not set, just a few of the problems.Jfriz

Although the flightdeck is not correctly set up, none of the things mentioned will prevent the AP being engaged. To prove the point I just made a takeoff without setting up the FMC, tuning radios, switching FDs on, arming autothrottle or retracting the gear. I selected CMD A and the AP engaged in CWS pitch and roll.Kevin Hall

FD is on and speed is set. FD bars are not showing as no modes are selected on the MCP and A/T has not been armed. V-speeds are not programmed and confirmed in the FMS either.Speed should however be set to V2 on the MCP and not 250.Geir J.

The A/T is armed but has not been engaged.Fred.

Although the flightdeck is not correctly set up, none of the things mentioned will prevent the AP being engaged. To prove the point I just made a takeoff without setting up the FMC, tuning radios, switching FDs on, arming autothrottle or retracting the gear. I selected CMD A and the AP engaged in CWS pitch and roll.Kevin Hall

That is true Kevin and can even be verified while on the ground.A lot of folks are not aware that you can push CMD A & B while on the ground.CWS P and R are the default autopilot modes when no other modes are engaged.You can even engage a pitch and roll mode but be very carefull with the autothrottle !!( for any pilot who hates his job and wants to get fired !........Arm the A/T......press CMD A and select ALT HOLD..........That should do it !! )Fred.

Edited January 1, 201214 yr by RYR738

Thanks to everyone for your comments; they led me to check a lot of things.I have just re-tried the flight and A/P is still not engaging, though I tried everything: I retracted the gear immediately, dialed in the proper course, dialed in speed VR+20, tried engaging VNAV before A/P (VNAV lit up but A/P wouldn’t – LNAV won’t light up, probably because I need to be on an intercept course first). Fred said “the A/T has been armed but not engaged”; is there something more I need to do about that? Flight director is on and CDU is correctly set up, I believe; V-speeds, including VR, are shown correctly in green on the speed display and voice announces VR and V2. Both flight director switches are on; F/O’s display also says “FD.”A/P will not arm on the ground. And, as described earlier, LVL CHG and HDG SEL appear to engage (lights turn green and MCP annunciates them) but they have no effect on aircraft movement.Additional headscratching (and critiquing!) most welcome. (And for the curious, altimeters are set to STD because it was a 29.92 day at KHPN!)Tom

While on the ground, Are you advancing the throttles to 40% N1 and then pressing TOGA ? ( with the autothrottle armed of course and both F/D's on.)That is how you would normally takeoff.As regards the 29.92 setting, there is no need to press the STD button untill above 18,000 ft. (Transition Level.)The numbers will turn amber to remind you. It's the same for descending........the STD will turn amber.(In most of Europe the transition level is 5000 or 6000 ft.)Fred.

Edited January 1, 201214 yr by RYR738

Tom, did you forget to press TOGA, when you have your engines stabilized at 40% ?Also, even if this has nothing to do about your isssue. Only dial in V2 in MCP speed window.The ac will try reaching V2+20, have a look on your speedtape and the bug there. (PFD)/ Leffe

Edited January 1, 201214 yr by Leffe

The A/T is armed but has not been engaged.Fred.

You're abseloutely right, don't know how I missed that one :)

Hi,how are your failures set? If you have service based or random failures on, it can be also malfunctioning autopilot (for example because of excessive force on yoke while AP on during previous flight)

Tom, did you forget to press TOGA, when you have your engines stabilized at 40% ?Also, even if this has nothing to do about your isssue. Only dial in V2 in MCP speed window.The ac will try reaching V2+20, have a look on your speedtape and the bug there. (PFD)/ Leffe

This is nothing to do with the AP not engaging. Learning correct takeoff procedures won't help Tom find out the cause of his immediate problem.Kevin Hall

Tom,You say the AP switch light flashes green momentarily. Does the red A/P P/RST light flash at all? It sounds to me like the AP is being kicked off as soon as you try and switch it on, maybe even too fast for the warning system to register it. Most of the things which should cause the AP to disengage automatically would be obvious from your screenshot (e.g. no hydraulic pressure), so it is probably something to do with your software installation. However a screenshot of the overhead would be useful just to be sure.What version of NGX are you running? If it's SP1b did you patch it over SP1 as per PMDG's announcement? When I upgraded to SP1b I patched from SP1 and this introduced some strange behaviour in the yaw damper and HGS. I reinstalled the NGX using the base package and then SP1b update and the problems disappeared. I wouldn't normally suggest reinstalling software without good reason, but patching SP1b did cause various problems for some people in the forum and may well have caused this problem for you.As for seeing modes like VNAV, LNAV, etc annunciated but having no effect, that is perfectly normal with FD on and AP not engaged. In this case they are providing guidance to the pilot in manual flight via the FD.Kevin Hall

Thanks again, everyone, for your input. Problem solved, at least for now. I started a brand new flight with a different airplane (the 737-800NGX instead of the 900) and the A/P functioned fine. The flight I was working from may have been created before SP1b.(I often set up flights for specific routes, up to the ready-for-takeoff point, so i have something to fly in a hurry). Everyone's suggestions helped a lot re my technique. Best for 2012 to all!Tom Kent