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Guest martinantispam

VOR/DME approach using VNAV?

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Guest martinantispam

Hello everybody,i tried to find something concerning this topic in the forum, but i could not find anything. I was practising the VOR/DME approach RWY09 at St. Maarten (TNCM/SXM) with the 747 yesterday. I followed the printed chart and went on till i got onto the 096 heading at the end of the procedure down to the MDA. For this procedure i could use LNAV perfectly as it was following everything programmed very smoth. The only thing that i was thinking about was a VNAV descend onto the runway. I read the manual and to tried to find out how to use VNAV so that it guides me the way with the FD down to the runway, but i couldn't find it. So I ended up using v/s which worked for me. Is there a way to use VNAV for the last 2200 feet (in SXM) down to the runway?Best regards,Martin Schiewe

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I have the PMDG 737 NG and the 744. I have successfully done a VNAV landing in the NG by setting the MCP ALT to zero (or to the altitude of the destination runway) and allowing VNAV to guide the a/c down to ground level or to within 50 vertical feet. You might be able to do something similar in the 744 although this is only a guess.Jonathan


Jonathan Sacks

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Martin-VNAV does not fit the regulatory parameters for Precision Approach Path Guidance to touchdown, so I'd recommend that you use it only to get yourself to the runway proximity.You can plug a waypoint in that is on the 3deg. glidepath and place it at the correct distance from the runway (300' / mile) and it will take you there....Honestly- I wouldn't want to be relying upon VNAV below MDA on the approach.... They invented hills to smite people who do. :-)I used to set up false glideslopes to compare the VNAV descent path caluclation to the ILS going into various airports on the east coast- and while "close enough" for a regional, i wouldn't rely upon them in something that drags it's feet this far behind.


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Guest D17S

As Robert says, it's not certified, yet . . . but it's all going to be happening within the next 5 years. Vnav approaches and autolandings will become common, A while back we were playing with this very thing. Here's a cut and past from a previous tread. "How low can you go with Vnav?We can go as low as we want. Just set up a normal flight plan with it terminating in an approach to a runway from the FMCs DEP/ARR/ arr page. Most of the Approaches I've seen have 3 or 4 waypoints at short intervals. This makes a nice tight set of vertical destinations for Vnav to aim at during that last final approach leg. Heck, just use those. 200 foot DH, Chicken! I was ready to let it land. It really worked that well. Make sure the legs page shows a full route with your runway's waypoint correctly set to field's elevation. Go fly.Fly the route in LNAV/VNAV and just leave it alone. Might want to set a 180 k speed restriction at a ways back. Start getting the flaps down. At 25 miles from the runway, you will still be L/Vnaving along. Double check that your altimeter is set to field baro. This is critical.Note that if you are within 25 miles of your runway, pitch will stay in VNAV PATH and thrust will stay in SPD. You can now start dialing down airspeed. Tap MCP's airspeed window knob and you will open the window. Thrust will keep you on-speed and Path will keep you on-path. Get into landing configuration and then to Vref soon as you can. Path is a bit wobbly. You want to give the AFS as much time as possible to get stable.Then just sit back and watch.The ILS will have autotuned and will be displaying LOC and GS info in the PFD. DO NOT PRESS APP! Watch the ND's path scale against GS. Make sure they are tracking the same. Watch LOC against versus the roll command bar. The roll bar is still displaying Lnav commands.At RA of 50 feet, look out the window. You are over the runway threshold.. Disco the AP and the AT, flare and rollout normally.Sam"As soon as Vnav gets hooked up to GPS, we will be another step along our way to using Vnav for approaches and autolandings.I understand Airbus is working on certifying a GPS based Vnav system now. . . . actually, everyone is. It's what's next. Fully ground independant navigation. But we can practice with the PMDG model right now. Great fun.

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Basically what it comes down to is; you can cheat using VNav in the sim when not flying an ILS appr. I've done it before with GPS approaches to below minimuns. It can be quite nail biting watching it fly all the way down until you're over the numbers.Just set an initial speed restriction at the "IAF" or first waypoint of the appr. (usually they're set up in a T configuration) (180 KIAS or whatever) then when the FMC updates itself (hopefully already done before the last fix in the appr.) set the VRef+5 in the FMC at the last waypoint (usually the rwy) in the FMC. Let it ride until you're ready to disco the a/p and a/t totally. Don't forget to plugin the altitudes at the waypoints also. SOme SID/STAR cycles don't have the GPS approaches in them I've noticed so you may have to manually enter them in. I can't remember who's NavData did or didn't have them.It can get very busy in the cockpit sometimes when you're trying to do all this also. If you're online you may not even get to it. I've botched up several approaches that way on Vatsim before...lol.Anyways, thanks for the fun topic guys. :-)

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