VNAV VOR approach help in 737

[VHOJT 177]

Hi allI was just shooting a VOR/DME approach onto RWY30 at YMHB in the 738. I was attempting to use VNAV down until minimums, or at least on initial approach.I have entered a few DME waypoints and their alitudes for the imaginary glidepath down to the runwa- one at 7 DME Of 2395ft and one at 5DME at 1755ft, so VNAV has a glidepath to follow.However, it follows it very badly - it drops engines to idle, and starts to descend rapidly (about 2000ft/min) just as it would if it were dropping from cruise alitude at TOD.I understand VNAV is used to conduct these sort of approaches until minimums fairly regularly - surely the real 737 doesn't behave like this? Or perhaps I am doing something wrong?Any suggestions would be very much appreciated!CheersRudy

[downscc 1,327]

I don't recommend VNAV on approach for many reasons... in fact I don't use it much at all for descents - only climbs. Easiest way to shoot a non-precision is to use the MCP Speed and V/S controls. A 800 fpm descent rate usually works, which at 160 kts is 300 ft/nm (800 / (160/60)) no wind.VNAV responds to an altitude constraint as if it were a "level off" altitude rather than a "descend through" altitude, and it often hangs-up after crossing a fix with a constraint (you'll see a magenta bug on the VSI tape). As you mentioned, you're going to hand fly below minimums anyway so you might as well get into the control loop throuhout the approach.