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Guest johnpc

PMDG 747-400 Help: Keep losing SPEED mode in AFDS

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Guest johnpc

I have a recurring problem, affecting about half my flights especially long-haul ones. The flight control system seems to "dump" the SPEED control function, with the readout disappearing from the top left of the AFDS. The result is no speed control, even though the A/P and autothrottle are still on. I've tried disengaging A/P, autothrottle, etc but no success.Is is possible to "reboot" the left AFDS SPEED readout and function (in flight)?John CAustralia

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Guest johnpc

Ryan,Thanks for the quick reply. I had already checked the info you recommended, but maybe I'm missing something. The situation I have is in the category of "ARMED and Disengaged (AT switch ON / no active mode)".The info says the AT system can be re-engaged: - By manual selection of any pitch mode - By pressing the SPD or THR buttons if the active pitch mode is not VNAV or FLCH. - By pressing the TOGA button if the active thrust limit is respectively TO or GA.The problem is that none of these actions seems to produce a response. Pressing the SPD or THR buttons is a non-starter, as neither becomes active. I've checked the manual, butI can't see any other way of manually selecting a pitch mode, except by the above action. Am I being stupid here (entirely possible) or is there some cunning trick to this?I'm not even sure what causes the problem---perhaps a sudden weather change?JohnAustralia

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Guest miggs

HiHappens to me too. try pressing tha VNAV button, it usually re-engages A/T. Regards , Mick

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Guest johnpc

Mick, thanks very much. That was exactly the problem, and when I checked the manual is does (rather discretely I think) mention having VNAV disengaged when re-selecting another mode. It solved the problem. It would be useful to see this one in a FAQ perhaps?Cheers,John

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