RNAV?

T

TheBusFlyer

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TheBusFlyer
Good evening,

Could anyone explain me how RNAV works?
Does it need GPS/GNSS?

Well, commercial planes like Airbus or Boeing use GPIRS - GPS primary to find there position. The FMGS' database has got each and every coordinate.
So what makes the difference between a simple GPS navigation and a RNAV navigation on commercial airlines?

Again, do we need GPS?

Thanks a lot,
TBF
 
Doesn't RNAV use no signal?
Radio Navigation Precesion? Are every commercial airline WPT RNAV?

An Airbus uses GPS to do a VOR approach. If RNAV uses GPS, what makes the difference?

Thanks
 
aRea NAVigation just means you are not limited to predefined corridors.

Using the Global Positioning System is one way of doing this; airliners may also have an Inertial Nav System that feeds into the computer as a cross-check and for further precision.

Generally, the difference between GPS, RNAV -0.1, RNAV -0.3, etc... approaches comes down to precision, tolerances, and $$$ of the installed equipment.

A VOR approach, of course, uses the VOR/VORTAC ground-based nav system for guidance.
 
warthog1984 said:
aRea NAVigation just means you are not limited to predefined corridors.

Using the Global Positioning System is one way of doing this; airliners may also have an Inertial Nav System that feeds into the computer as a cross-check and for further precision.

Generally, the difference between GPS, RNAV -0.1, RNAV -0.3, etc... approaches comes down to precision, tolerances, and $$$ of the installed equipment.
Click to expand...
That was generally my understanding as well.

I thinks some of the first RNAV equipment for for GA used ground based VOR signals to synthesize waypoints. But that just a memory from reading some
Flying mag articles.
 
Thanks a lot,

An Airbus/Boeing uses GPS to navigate.
But their RNP is very precise. What else has Airbus/Boeing installed to get so much precesion? If you just select a VOR approach, it will never be as precise as a RNAV approach. So Airbus/Boeing has something more than GPS for RNAV....

Please explain;
Thanks!
 
" Inertial Nav System" , what is that?
How does it cross-check? Is it simply IRS/INS?

Yes, but again, for a VOR approach, Airbus uses GP-IRS. For an RNAV approach, Airbus uses GP-IRS.
But RNAV approach is more precise than a VOR approach.

So what makes the difference?
 
TheBusFlyer said:
Thanks a lot,

An Airbus/Boeing uses GPS to navigate.
But their RNP is very precise. What else has Airbus/Boeing installed to get so much precesion? If you just select a VOR approach, it will never be as precise as a RNAV approach. So Airbus/Boeing has something more than GPS for RNAV....

Please explain;
Thanks!
Click to expand...
I think the answer is GPS/W or WAAS (Wide Area Augmentation Services). We all have access to that accuracy with devices like the ubiquitous G430W.

But I'm just talking and don't really know, so....?
 
TheBusFlyer said:
Thanks a lot,

An Airbus/Boeing uses GPS to navigate.
But their RNP is very precise. What else has Airbus/Boeing installed to get so much precesion? If you just select a VOR approach, it will never be as precise as a RNAV approach. So Airbus/Boeing has something more than GPS for RNAV....

Please explain;
Thanks!
Click to expand...

The Boeings use a mix of GPS along with IRSs. The IRSs keep themselves updated by auto tuning VORs along our route and use DME/DME updating.

As a matter of fact, our 757s don't have GPS installed at all but we an navigate using RNAV routes enroute but can not fly GPS/RNAV approaches.

If you fly a VOR approach we use the VOR, not an RNAV overlay.
 
Hmm .....Thanks!

But Airbus uses a GPIRS hybrid position.
So how do you fly RNAV with no GPS?

Thanks
 
TheBusFlyer said:
" Inertial Nav System" , what is that?
How does it cross-check? Is it simply IRS/INS?

Yes, but again, for a VOR approach, Airbus uses GP-IRS. For an RNAV approach, Airbus uses GP-IRS.
But RNAV approach is more precise than a VOR approach.

So what makes the difference?
Click to expand...

Are you an FSX/X-Plane "pilot" by any chance? We fly real planes in this forum, just so you know.

But, here goes:

1) Inertial Nav System = I.N.S. The equipment mathematically calculates the plane's position based on a starting point and acceleration over time.
2) Global Positioning System = G.P.S. A constellation of satelites allows the equipment to compute a position in real time.
3) Very high frequency Omnidirectional Radio range = V.O.R. A ground-based beacon sends out a directional signal and the equipment shows which direction you are relative to the beacon. More precision the closer you get to the beacon. By definition, NOT RNAV.
4) Instrument Landing System = I.L.S. A precision version of a VOR which also sends out a vertical signal within a smaller area.

The more of the above you have, the more info you (or your computer) has and the more you can exactly locate your position. The tighter tolerances in the equipment, or more precise equipment you have, the better your "fix" is.
 
Agreed. But an Airbus doesn't "wait" for VOR signals to come.
It uses GPIRS. You can check it in the F-COM...
GPIRS is calculated by the ADIRS/ADIRU.

Thanks
 
TheBusFlyer said:
Doesn't RNAV use no signal?
Radio Navigation Precesion? Are every commercial airline WPT RNAV?

An Airbus uses GPS to do a VOR approach. If RNAV uses GPS, what makes the difference?

Thanks
Click to expand...

The Airbus can use GPS overlay for a VOR approach, or you can use the VOR.

Question: Do you really fly a B757? :dunno:
 
TheBusFlyer said:
Good evening,

Could anyone explain me how RNAV works?
Does it need GPS/GNSS?

Well, commercial planes like Airbus or Boeing use GPIRS - GPS primary to find there position. The FMGS' database has got each and every coordinate.
So what makes the difference between a simple GPS navigation and a RNAV navigation on commercial airlines?

Again, do we need GPS?

Thanks a lot,
TBF
Click to expand...


These days for all practical purposes in GA, yes, it requires a GPS installation.

RNAV is just an acronym for Area Navigation, and there are other systems. Inertial Navigation Systems are still in use in big airliners, but are being phased out due to costs.

There is the KNS-80 Rho Theta system that works off VOR stations. You still see them every once in a while, but anymore the owners have no clue how to use it for the most part and never gets turned on.

There was also LORAN and OMEGA terrestrial based systems that were used for aviation RNAV prior to GPS that are now defunct with no operating transmitters (although LORAN may yet return).

In the end, GPS is the lowest cost, simplest way, to fill the precision location needs of many industries around the globe.
 
Last edited:
Thanks,

So just a simple question:
As R&W said, VOR approach, on Airbus uses GPS.
Of course, you can fly it manually by tuning the VOR in the FMGS.

There is also Aera Navigation - RNAV.
There are RNAV approaches. But an RNAV approach is much more precise than a VOR approach (everything is automatic). What makes RNAV approach with A/P ON more precise than a VOR approach with A/P ON?

Thanks
 
TheBusFlyer said:
Thanks,

So just a simple question:
As R&W said, VOR approach, on Airbus uses GPS.
Of course, you can fly it manually by tuning the VOR in the FMGS.

There is also Aera Navigation - RNAV.
There are RNAV approaches. But an RNAV approach is much more precise than a VOR approach (everything is automatic). What makes RNAV approach with A/P ON more precise than a VOR approach with A/P ON?

Thanks
Click to expand...

Vertical guidance.
 
TheBusFlyer said:
There are RNAV approaches. But an RNAV approach is much more precise than a VOR approach (everything is automatic). What makes RNAV approach with A/P ON more precise than a VOR approach with A/P ON?

Thanks
Click to expand...

Where do you see that an RNAV approach is more precise?
 
Honestly, reading this thread and lots of the inaccuracies you've posted, it frightens me to think that you may actually fly a real airplane.
 
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