Hi Gents, I've flown a couple of sectors and noticed something that doesn't seem right (or maybe I've just got too used to the old FS9 PMDG 737NG way of working). I fly with FSX default ATC and they often give descent clearance after Top of Descent (TOD). At TOD (in VNAV mode) the throttles slowly close as the speed bug decreases and the Aircraft decelerates significantly. At best I thought it would switch from VNAV to ALT HOLD, but actually slowing the A/C uncommanded seems somewhat perilous. I'm fairly sure it's going to Descent Power rather than Descent Speed, but haven't analysed it precisely. The speed drop observed has been as much as 50kts before I get eventually get descent instruction from FSX ATC and start down. Cheers Chris.

I believe it is normal behaviour, as it thinks you have missed the t/d and is doing what it can to help you regain the profile once you do start down... Andrew

As Andrew said, this is normal. The jet is just trying to get rid of the extra energy you're building by staying above profile. It's trying to shed the potential energy by reducing the the kinetic energy now.

Boeing calls this "Energy Compensation" -- see the FCOM volume 2, page 11.31.30. -- Martin Boehme

Thanks for the info here Folks, good to know this is genuine behaviour. Cheers,Chris.