Can't get V/S to engage on this flight

[Vauban 0]

Here's another question for you PMDG experts - it concerns the B737-700: I normally have no problem with selecting V/S, but right now it won't engage.I was flying on A/P HDG and LVL CH, then used VOR/LOC to capture a course to a VOR - this is the only unusual (for me) factor on this flight. The FMAs show MCP SPD/Blank/ALT HOLD. The gear's down, I'm sitting over the FAF at approach altitude, and I've just arrived at Vref+5 with landing flaps. SPEED and A/P the only lights on the MCP.Now I want to descend, click V/S (that's what I'm using on this flight) and nothing happens - it won't engage.Any bright ideas out there??GeoffEdit: Well, I just pushed the nose down and after a few seconds I was able to engage V/S. Does that give you a clue?

[Guest Daniel Pimentel]

Is the altitude dialed in lower than the altitude you're presently on? Wild guess here.Daniel P.http://www.precisionmanuals.com/images/forum/supporter.jpgMember of SJU Photography. [A HREF=http://www.jetphotos.net/showphotos.php?userid=9004]Click Here[/A] to view my aircraft photos at JetPhotos.Net!The official psychotic AA painter. :)

[Vauban 0]

Thanks Daniel, I wonder if that's what it was - having ALTITUDE set to my current altitude and not to TDZE? I'd like to think I'm smart enough to have seen that at the time. The fact that I was able to select V/S after I pushed the stick forward tells me that can't be it. But then maybe I set ALTITUDE to TDZE just before I pushed the stick forward. Nah, I'd remember doing that, right?Geoff

[cowpatz 243]

I would put my money on that being the case. Sometimes you can vert speed away from an altitude that is the same as the MCP altitude. This may occur because the actual altitude may be just below the MCP alt, but barely enough to notice. If it is the same or just ever so slightly above then it will not engage or might engage for a short time and then capture the altitude. Its OK it catches lots of people out.CheersSteve

[Vauban 0]

Thanks Steve, now I know what to look out for if it happens again - which is why I posted in the beginning.Geoff