Hi Can anyone tell me what the possible reasons are for a VNAV disconnect on the 737. I can find LNAV reasons in the manuals but not for VNAV. I am finding this problem if I disconect to go to V/S or LVL CHG and then wan to go back to VNAV after, if that helps ?MTIASteve

When you try to return to VNAV are you adhering to any altitude restrictions set on the leg you are flying ?Peter

Hi PeterYes, as I had the same thought. Steve

If you overspeed or reach vmo/mmo it will revert to lvl ch. Under 10' I believe it is more restrictive soi watch your speed and use the speedbrakes when you get DRAG RQ................Randy J. Smith................A PROUD MEMBER OF THE PMDG BETA TEAM[h4]Evolution is a process that results in heritable changes in a population spread over many generations[/h4]

Thanks Randy, in this case I was far from VMO (220KIAS), this is perhaps a more complicated question than thought. When/if it happens again I will note the scenario better.CheersSteve