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Guest glenb

RNAV Approach FMC MCP setup

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Guest glenb

Hi,I have no problem using the FMC and MCP up to the Initial Approach Fix (IAP) and usually to the Final Approach Fix (FAF). After the FAF the FMC/VNAV no longer controls the aircraft for the decent to the Decision Altitude (DA).How should the Legs page of the FMC be set up and when and what settings are entered into the MCP for a RNAV approach?A short flight from Tucson TUS to Phoenix PHX using the RNAV (GPS) RWY 26 Approach for Phoenix Sky Harbor Intl (PHX) for example.Set weather to clear.Selecting RNAV for runway 26 and the IWA transition prior to takeoff and entering the following in the legs pageIWA 170/6100EVXAF 160/4000YOKXO 150/3000Cruise at 16000 (short flight).While at cruise select flaps 30 degree in INT page and set the MCP course to 258.The question is; What setting for altitude and where in the MCP for the decent?If I set the altitude to 0 prior to TOD and lower flaps to 15 prior to IWA the approach will be smooth to the runway threshold. I have tried many combinations of altitudes (which did not work), setting to 0 works but does not seem correct.

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Hi Glen,Make sure the NAV 2 radio is set to the correct ILS frequncy. When using the ILS, the autopilot gets its roll and pitch information from the NAV 2 radio. Make sure you hit the Autopilot B. Some airports have a Catagory III autoland system. This means that it will fly the airplane down to the runway and flare the airplane. In case you don't know, the LNAV controls lateral movements of the airplane, or the direction. The VNAV controls vertical movements and tells the autopilot when to start a decent at a particular fix. When you're on final approch, make sure the ILS/VOR captures the ILS localizer. This will be indicated at the top of the primary flight display when the ILS/VOR turns to green. Be sure you press the APP button on the MCP so it will capture the glide slope and start the decent. Hope this helps.Ken.

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Guest frankathl

Hi Chris,Not an answer to your question(see Ken's above), but what do you mean by "Selecting RNAV for Runway 26"?Thanks,Frank

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Glenn,Set the MCP altitude window to VNAV DA(H) minimums. If the approach doesn't have VNAV DA(H) minimums then you should set the MCP altitude window to MDA + 50 feet. Only approved carriers can use VNAV DA(H)minimums. Start the MAP a this altitude. The airplane is permitted to dip through VNAV DA(H) just like dipping through an ILS DA. The reason 50 feet is added to MDA minimums, is to prevent the airplane from dipping below MDA. You should set the MCP altitude window to approach plate minimums at least 2 miles from the FAF after being cleared for the approach by ATC. Once the airplane is established and stabilized on the VNAV PTH descent and about 1000 feet above either VNAV DA(H) or MDA , reset the MCP altitude window to the MAP altitude. The airplane will continue to descend to minimums.Set either VNAV DA(H) or MDA + 50 feet in the minimums baro window prior to beginning the approach.Aloha,Floyd


John Floyd

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Guest frankathl

Thanks for the reference, Michael. I had a look, but the meaning and application still seem to elude me,just as before :-(. The closest I can get to a definition so far, is from this site:http://www.allstar.fiu.edu/aero/RNAV.htm"Area Navigation (RNAV) can be defined as a method of navigation that permits aircraft operation on any desired course within the coverage of station-referenced navigation signals or within the limits of a self contained system capability, or a combination of these.RNAV was developed to provide more lateral freedom and thus more complete use of available airspace. This method of navigation does not require a track directly to or from any specific radio navigation aid, and has three principal applications: A route structure can be organized between any given departure and arrival point to reduce flight distance and traffic separation; Aircraft can be flown into terminal areas on varied pre-programmed arrival and departure paths to expedite traffic flow; and Instrument approaches can be developed and certified at certain airports, without local instrument landing aids at that airport. Navigation systems which provide RNAV capability include VOR/DME, DME/DME, LORAN C, GPS, OMEGA and self contained Inertial Navigation Systems (INS) or Inertial Reference Systems (IRS)."So, from this explanation, and a good example farther down on the quoted page, it seems that RNAV allows an aircraft to fly routes other than from navaid to navaid by flying offset to the ground stations, thus offering a more direct route from departure to destination.I have looked at the approach charts for Rwy 26(L&R) at KPHX, and the most obvious difference from other approaches is that the approach path is composed solely of intersections, without any direct use of ground based stations(I also noticed that the PXR VOR is referenced on the charts, but without any frequency or Morse code information, which I find strange?). By contrast, if you look at the VOR DME approach to 26 L, you will see that the PXR VOR(with full information this time), is part of the approach.These are GPS approaches, but I conclude from the explanation of RNAV, that aRea NAVigation could also be performed in LNAV with a suitably programmed FMC.This is as far as I can get in understanding RNAV, so far. I would be grateful if someone could explain further, ideally with actual examples, as above.Thanks,Frank

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Frank, you missed the key ingredient here. It is not the LNAV part it is the VNAV part. RNAV/VNAV aproaches are unique because they allow (some) aircraft to fly ILS-like approaches without the ILS. The vertical part can be either done through WAAS (GPS) or VNAV-baro. I think Alaska Airlines have permission to fly such RNAV/VNAV approaches into some Alaskan airports. Please re-read the document I gave you the link fo and pay attention to the vertical navigation part which is really what it is all about.Michael J.WinXP-Home SP2,AMD64 3500+,Abit AV8,Radeon X800Pro,36GB Raptor,1GB PC3200,Audigy 2


Michael J.

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Guest glenb

Thanks to all for the help and comments.Michael the link is great. It contains a lot of info from the horses mouth (FAA).Floyd the procedure works. A question though; I can only enter altitudes rounded to 100 feet. I cannot enter a DH of 1560. I round down to 1500.When a RNAV approach works like it should it is a pleasure to watch. An approach can be made from cruise, hands off, to the DH, except to lower flaps and gear and maybe a little drag.To clarify a few things.Phoenix has three runways7R/25L7L/25R8/26There is no 26L or 26RIt is the RNAV (GPS)RWY 26 approach that I referred to. This is not an ILS approach. Seehttp://avn.faa.gov/d-tpp/0501/00322R26.PDFThis approach is selected on the DEP/ARR page of the FMC for KPHX as RNV26.The manual, chapter 10 page 10 has info about flaps to 15 before 15 nm of the airport.My observations after more trial and error (lots of error).The fix altitudes on the approach plate are "at or above" and that is the way it is in the sidstar file for KPHX. If I use those altitudes which show up as ___/4000A the approach fails by not maintaining the VREF. If I change the altitudes to simply "at" ___/4000 the approach is perfect. The speeds are entered of course.It's all a lot of fun.

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Guest frankathl

Thanks for your further comments, Michael. I did read the document you referred to again, but I'm afraid there is too much information there for me to handle at the moment(sorry! :-().I think we are approaching RNAV from different angles(pardon pun!). It was natural for you to interpret my request for information as referring to RNAV Appoaches only(this was Glen's topic and, anyway, I didn't explain myself very well), but I was, in fact, referring to the concept of RNAV, generally, which I have struggled to understand for some time. If you go to the link I provided, you will see that a means of lateral navigation, such as LNAV or VOR/DME is, in fact, required for flying an RNAV route, as the straight line route is often offset from the position of the ground stations.Just to rephrase my request and put it more specifically again:The concept of RNAV seems more complex than other navigation methods(VOR/DME, NDB, ILS, etc). What is the background to the development of this method and how, in general, does it function? If possible, give examples of RNAV in use.I do appreciate the help and reference but, at this stage, I would prefer a simple explanation of the basic general idea(being just a humble flightsimmer, not a pilot), something I can use to follow the more complex discussions, such as on the FAA site.Many thanks again,BR,Frank

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Guest frankathl

Hi Glen,Gee, I don't know what I was looking at, then??? My copy of Simcharts is old(version 1.0), but I don't imagine KPHX built(or decommissioned) a runway since 1999! :-). I'll have to go check again when I get home, but, unless I was at the wrong airport(!!), I'm sure there were approach charts labelled 26L and 26R.BR,Frank

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Hi Frank,"The concept of RNAV seems more complex than other navigation methods (VOR/DME, NDB, ILS, etc). What is the background to the development of this method and how, in general, does it function? If possible, give examples of RNAV in use."I don


George Morris

 

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Guest frankathl

Hi Glen,I checked my charts again and, sure enough, Jeppesen did publish approach charts for GPS 26L, VOR DME 26L and GPS 26R, ILS 26R in 1998(not specifically labelled RNAV). I noticed that now, the runways are 25L, 25R, and 26. Could this have anything to do with polar magnetic variation(so that 25L/R were once 26L/R)?BR,Frank

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Glenn,>Floyd the procedure works. A question though; I can only enter >altitudes rounded to 100 feet. I cannot enter a DH of 1560. I round >down to 1500.Great.Round the altitude up. Never down. So in this case, set the VNAV DA(H) to 1600. Let me add something else.After the airplane has passed the FAF and is stabilized in the VNAV PTH descent and about 1000 feet above 1600 feet, reset the MCP altitude window to the MAP altitude. The airplane will continue the descent to minimums. At minimums, if the airplane is in a position to land, disconnect the autopilot and set the F/D switch to OFF then ON. You should see FD on the PFD without the command bars in view. Doing this makes the F/D available for a F/D Go-Around if needed. Hand fly the landing using the VNAV deviation pointer like a glide slope to the runway or use the VASI. If the airplane is not in a position to land push the TO/GA button and go-around. Your F/D command bars will pop into view for the go-around.Floyd


John Floyd

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Guest glenb

Floyd,Very helpful. Thank you.One other question. On some approaches the FMC will not maintain the Vpath and it seems like it is related to a fix on the log page with a "at or above" constraint. If I remove all of the "at or above" constraints and re-enter as 170/5000 (no "A") the approach goes well. Have you noticed the same?Glen

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