RNAV/GPS approaches - how are they modelled in PMDG planes?

[mozart 1]

There is a lot of talk about RNAV/GPS approaches and how they are more precise and independent than ILS approaches. Therefore I was wondering to what extent the PMDG 737 and 747 do model this. If it is modeled, how do I fly them? Assuming that I have my flightplan including the STAR and all the speed and altitude constraints properly programmed in the FMC, do I just leave LNAV and VNAV on until I touch down? In other words, is it like an

[Guest capntom]

Hi:Autoland is not feasable when operating in other than the two or three autopilot ILS approach mode (Land 2 or land 3 displayed). This is not available in VNAV/LNAV. These approaches typically will have a MDA. When 300' below the final approach fix alt, set the missed approach altitude and continue descent in LNAV/VNAV. Either disconect the autopilot and authrottle and land if the runway is in sight, or miss approach at the appropriate point for the approach in question.Good Luck! Tom

[Farlis 2,287]

>There is a lot of talk about RNAV/GPS approaches and how they are >more precise and independent than ILS approaches.Curious that they don't count as precision approaches, isn't it? ;)

[Guest D17S]

ChrisIt

[zubart 5]

Here are the steps to do an instrument approach using VNAV in a 737NG. This is one way of probably many and probably not much different in a 744. Rnav approaches are not autolands. The airplane will level off 50 feet above the runway touchdown zone if useing the autopilot or hand flying with the FD (flight director). The biggest feature not modeled on the LEGs page is ANP/RNP or Actual Navigational Performance verses Required Navigational Performance . In a real FMC, the RNP 0.3nm must be inserted on the legs page for RNAV/GPS approaches. Sometimes you may see a note about this on the approach plate.Recommended roll modes for final approach:RNAV, GPS or TACAN approach : LNAVLOC-BC, VOR or NDB approach: LNAV or HDG SELLOC, SDF, or LDA approach: VOR/LOC or LNAVFor LOC, LOC-BC, SDF or LDA approaches, ensure appropriate navaids are tuned and identified prior to commencing the approach and monitor raw data throughout the approach. For VOR and NDB approaches, raw data should be monitored, if available.FMC approach procedure................SelectSelect the approach procedure on the ARRIVALS page. DO NOT MANUALLY BUILD THE APPROACH OR ADD WAYPOINTS TO THE SELECTED FMC PROCEDURE. Add cold temperature corrections to waypoint altitude constraints as appropriate.Verify VANV glide path angle is displayed on the final approach segment on the LEG's page.RNP appropriate for approach (if required)...Verify/Enter, this allows appropriate alerting to occur if ANP exceeds RNP.Approximately 2 NM prior to the FAF and after ALT HLD or VNAV PTH engaged:MCP Altitude......................Set MDA(H)/DA(H), This allows VNAV to command descent in VNAV PTH. If the MDA(H)/DA(H) does not end in zero zero, for example, 1320, set MCP ALTITUDE window to the closest 100 foot increment above the constraint. There may be a level segment beyond the FAF before intercepting the descent path.Prior to reaching FAF:AFDS roll mode ...............Verify/Select, verify appropriate roll mode annunciates.VNAV switch (if required) ....................Push, select VNAV if in ALT HLD. Verify VNAV PTH annunciates.Autopilot......................Verify engaged, the autopilot should remain engaged until suitable visual reference is established.Prior to reaching MDA(H)/DA(H) and when the airplane is at least 300 feet below the missed approach altitude:MCP altitude....................Set missed approach altitude.At MDA(H)/DA(H)/Missed approach point:If suitable visual reference is not established, execute a missed approach.After suitable visual reference is established:A/P disengage switch.......................Push, disengage the autopilot before descending below MDA(H)/DA(H).A/T disengage switch...............Push, disengage the autothrottle before descending below MDA(H)/DA(H).Floyd

[mozart 1]

Thanks a lot guys. Just confirmed what I thought:1) vertical navigation is still a bit unprecise2) relying purely on LNAV to make turns just "inches" before the base (e.g., as is needed for KDCA, LOWI, LPMA, SBRJ and some others) may be taking risks- in the end, I have to hand-fly her. Fine with me as well, leaves me with a challenge...!ThanksChris