I have been practicing flying the RWY 27 RNAV approach into Tampa KTPA. Is it possible in the real 737 to hit the approach button and have the plane automatically track the glide slope? Can these 2 be coupled? Or do you have to roll the V/S dial to go down the G/S? If it IS possible, what am I doing wrong? When I press APPR., I always get the predictable FMC error message "Navaid invalid." Anyone?Chris Catalano

Intercepting the localizer is easy enough but if you want to intercept the glide slope you must be below it in level flight or in a shallow descent so the glide slope can cross your path from above. In that moment if you have armed G/S mode it will engage automatically and manage the descent profile of the plane.If you intercept the localizer and you are above the G/S, then you must use other method to descent and cross it, in order for the G/S mode to be engaged.I don

He is talking about a RNAV approach, not an ILS approach. That is a "by position" approach, not a "radio approach".Have you tried to fly it with VNAV engaged ?Jose Luis.

Chris,The APP button is going to track a localizer and glideslope from an ILS station, nothing else.I do believe some versions of the real NG's FMC software are certified to do a VNAV approach though, which is basically what you're asking here. What you would do here is basically conduct the entire approach in LNAV and VNAV - LOC and GS mode and the APP button are not used at all, your path exists completely in the computer with no raw data from an ILS, VOR, NDB, etc.You just input the altitude restrictions from the chart (they should already be there from the IAP database in real life) and let VNAV step you down - at your minimums you disconnect the AP and land if you have the runway in sight, or else you go around. Works just like any other instrument approach.You can certainly try it in the NG, but I'm not sure we'd advanced to that point yet with our FMC modelling. Our 747 is fully capable of doing these VNAV approaches though and I'm sure the NGX will be as well...

so if you engage APP and LOC on this approach would you be doing the RNAV approach wrong then ?

Let's see what RNAV is.RNAV means aRea NAVigation. It is a navigational system not based upon radio navaids but in the capability of modern aircraft to precisely determine their global position (Inertial Reference Systems, GPS...)RNAV routes are basically lines that not depend at all on VORs, NDBs...So, the number of routes can be greatly increased helping in the handling of traffic in congested areas.A RNAV approach is flown following vertical and lateral position, not following radio signals.Jose Luis

a ha so a RNAV approach doesnt use fixes?:-hmmm

Yes, it can use "fixes" but they can be or not referred to VORs, NDBs...The "fixes" have N,S,E,W coordinates and vertical Z position if needed, and that is enough.Jose Luis

so then its simply a matter of inputting the fixes in the fmc of the 737NG to fly the RNAV route taking into consideration speed and altitude?

And "old fashioned" navaids (VOR,NDB,DME) will be only used (autotuned by the aircraft) to obtain redundant information and increase the accuracy of the system.Jose Luis.

sweet, thats what ive been doing all along flying these approaches, so atleast ive been doing something right, but i still use the APP/LOC system to guide me down to minimums.

>so then its simply a matter of inputting the fixes in the fmc>of the 737NG to fly the RNAV route taking into consideration>speed and altitude?But, of course, you can not make your own RNAV route, you must fly a published one. (Well, that is in real life, in FS9 you can do as you prefer...)Jose Luis

well i dont make up the route, i always review a RNAV diagram and plug in those waypoints and fly that. http://forums.avsim.net/user_files/151817.jpg

Ryan,I've done it with your NG. It does work just fine. Just make sure you choose an approach that's not offset...LOL.I usually dial in Vref+5 at the first "straight in fix" so to speak.It means that you have to wait until almost the last minute to start inputting the final speeds.I've been successful down to well below any proper minimums...rofl. It's a nail biter, but loads if fun when you can make it happen.

I have NOT tried it with VNAV engaged. I will have to try that next. Thanks for the suggestion.Chris Catalano