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GPS v. NAV


pdmike

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If you are flying GPS, why is it necessary to have the GPS/NAV switch on GPS? Sounds like a silly question, but consider this.

 

I load a flight plan and take off with the GPS/NAV switch set to GPS. The GPS gives me the vector for the first leg. I get on it and the GPS keeps me on it, giving me the direction to fly (CTS) as well as other information, such as distance and time to the destination waypoint.

 

The thing is, while all this is going on, I can switch the GPS/NAV switch to NAV, and nothing seems to change. The GPS still keeps giving me the same information as I go from waypoint to waypoint.

 

So I say again - why is it necessary to have the GPS/NAV switch on GPS? Switching it to NAV in order to pick up the localizer is just one more thing to remember at that point. Why not just leave it on NAV all the time?

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The GPS gives you the same info, but the autopilot takes its input from whichever source is selected by the GPS/NAV switch. If you're flying manually it's not as important, except in certain situations, such as on the ILS. It's all to do with the functions of each system and the way things are wired, which reflects what it's like in real aircraft.

 

To clarify this for yourself, fly a flight plan (Direct or other) on AP with the switch in GPS and watch what happens with both the GPS and the NAV radios. Then fly with the switch in NAV position and notice what happens with the GPS and NAV radios, but also notice what you have to do to get the AP to automatically follow your flight plan, whether it's direct to on the GPS or individually selecting the NAV setup to get you there.

 

Then do VOR, GPS and ILS approaches with the switch in each position, and note what happens to guidance. For example, while the GPS can give you the localizer on the ILS approach, it can't give you the glideslope, there there are special functions available to get vertical guidance, but it's not the glideslope from the ILS.

 

There's more, but you can learn exactly what happens by flying these comparisons, and it'll stick with you better than if you depend strictly on narrative.

 

Larry N.

As Skylab would say:

Remember: Aviation is NOT an exact Science!

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If you are flying GPS, why is it necessary to have the GPS/NAV switch on GPS? Sounds like a silly question, but consider this.

 

I load a flight plan and take off with the GPS/NAV switch set to GPS. The GPS gives me the vector for the first leg. I get on it and the GPS keeps me on it, giving me the direction to fly (CTS) as well as other information, such as distance and time to the destination waypoint.

 

The thing is, while all this is going on, I can switch the GPS/NAV switch to NAV, and nothing seems to change. The GPS still keeps giving me the same information as I go from waypoint to waypoint.

 

So I say again - why is it necessary to have the GPS/NAV switch on GPS? Switching it to NAV in order to pick up the localizer is just one more thing to remember at that point. Why not just leave it on NAV all the time?

 

Read Aircraft Instruments, to learn what, and how, they do what they do..

https://en.wikipedia.org/wiki/Flight_instruments

GPS is NOT an ILS indicator, nor can it be misconstrued as such.

They are different, with COMPLETELY different functionality!

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Read Aircraft Instruments, to learn what, and how, they do what they do..

https://en.wikipedia.org/wiki/Flight_instruments

GPS is NOT an ILS indicator, nor can it be misconstrued as such.

They are different, with COMPLETELY different functionality!

 

Thanks. Yes, I did notice that so long as I am in GPS mode, with an ILS frequency on Nav1, if I have Nav1 activated, the morse code comes on, but that's all that happens. No indication of distance from the airport and no interception of the localizer.

 

Thanks for the link. I'll sure take a look.

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The GPS gives you the same info, but the autopilot takes its input from whichever source is selected by the GPS/NAV switch. If you're flying manually it's not as important, except in certain situations, such as on the ILS. It's all to do with the functions of each system and the way things are wired, which reflects what it's like in real aircraft.

 

To clarify this for yourself, fly a flight plan (Direct or other) on AP with the switch in GPS and watch what happens with both the GPS and the NAV radios. Then fly with the switch in NAV position and notice what happens with the GPS and NAV radios, but also notice what you have to do to get the AP to automatically follow your flight plan, whether it's direct to on the GPS or individually selecting the NAV setup to get you there.

 

Then do VOR, GPS and ILS approaches with the switch in each position, and note what happens to guidance. For example, while the GPS can give you the localizer on the ILS approach, it can't give you the glideslope, there there are special functions available to get vertical guidance, but it's not the glideslope from the ILS.

 

There's more, but you can learn exactly what happens by flying these comparisons, and it'll stick with you better than if you depend strictly on narrative.

 

Great stuff, as usual. Read and acknowledged. I will do as suggested and learn from it.

 

One thing, though. I have not been able to figure out how to get AP to automatically follow my flight plan. It seem that whicheveer I have the GPS/NAV switch set to, I have to manually set the new vector when I come to a waypoint. Any thoughts on this?

Edited by pdmike
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The switch merely changes your ability from having the GPS guide your aircraft to using a VOR or ILS to guide your aircraft. That is all.

 

I'm not at the point yet where I can have the GPS guide the aircraft. How do you do that? I think I am loading the flight plan properly. Could that be the problem? If not, what?

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Try pressing the VOR/LOC button with GPS mode selected. (While flying!! (And don't forget to have Autothrottle engaged as well.))

il.

 

I did as instructed on a flight from LAX to Sacramento. Worked like a charm. Thank you so much. Although, I will say, flying that way is a little boring. I think I prefer to make vector adjustments from time to time and do the other things necessary to fly the plane myself. But, at least, thanks to your instruction, I have added a new factor to my flight arsenal.

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I did as instructed on a flight from LAX to Sacramento. Worked like a charm. Thank you so much. Although, I will say, flying that way is a little boring. I think I prefer to make vector adjustments from time to time and do the other things necessary to fly the plane myself. But, at least, thanks to your instruction, I have added a new factor to my flight arsenal.

 

Week done! Good on you!

Happy Flights,

il.:cool:

[sIGPIC][/sIGPIC]
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