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FMC NG737 question

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When selecting an approach on the arrivals page there are several choices such as ILS and RNAV's. My question is, what the differance is between ILS and RNAV approaches? I would appreciate it if someone could help me with this.Thanks,Irv Strongin

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John,Thanks for the information. Have used ILS and visual landing techniques, but never GPS....don't even know if this is possible with FS9.Best regards,Irv Strongin

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It is possible, however you will never get a RNAV/GPS approach from FS ATC when your Aircraft is capable of doing ILS-approaches and your destination airport has one available.

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Thanks for the reply. What kind of equipment is necessary in the aircraft to enable it to take advantage of a Rnav approach? As far as I can see the NG737 is not equiped with GPS receivers. There was some mention of the use of GPS in the Pos INIT. Are localizer and glide slope captures possible with a GPS system and if so what type of receivers are used.Thanks,Irv Strongin

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The 737NG, in fact, has two gps recievers. You just don't have any direct interaction with them as you might in a smaller plane. The two gps are just two of the sensors used by the FMC for navigation purposes. So the FMC is perfectly capable of flying an RNAV approach.

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Dave,Thanks for the response...I just don't understand the mechanics of the RNav approach if you have no interaction with the GPS...is what you see on the ND dircted by the ILS from the particular runway or from a GPS system or the appoeach itself directed from navaids or GPS?Irv

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The approach procedure is loaded into the FMC as a series of waypoints (possibly with altitude constraints). The airplane uses the GPS sensors (and other sensors) to fly the appropriate path.That's one of the reasons GPS approaches are now called RNAV approaches. MOST of the time you need to have GPS sensors aboard to fly them, but some airplanes can meet the required tolerances (called Required Navigation Performance, or RNP) without GPS.

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Tim, Thanks for explaining RNAV to me....I understand it now.Best regards,Irv Strongin

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