Purpose of VOR tuning all the way while flying?

[LikeABoss]

Apologies for the silly question firstly, but how important is it to us that the aircraft keeps auto tuning itself to VOR's?

I understand at take off you have to have your VOR tuned to see if you're on the right radial etc while using the SID on the departure plate.
Once you're going according to you flight plan, what good is VOR tuning at this point?

You are going to be flying the magnetic tracks given in your flight plan to your way points, but why do you need the VORs tuned?

Again sorry for the silly questions, but i'm very confused with this, can somebody explain to me how it works please.

[tom775257]

Just as a way of updating the radio position of the aircraft navigation systems. The aircraft will use probably GPS if available, DME/DME for very accurate position check, then VOR/DME, finally VOR/VOR. It will autotune using the FMC/FMGC etc. The aircraft will also have the IRS position, individual and mix. A Kalman filter is used (if memory serves) to integrate these various positions to give the best known position to other systems eg. Navigational display. The freqs are pulled from a Navaid database.

The aircraft whilst flying a SID will be using the FMC/FMGC computed position to fly it in managed nav mode (or LNAV Boeing style), not raw data (which you can cross check against or fly if the FMC dies.

If you lose GPS and VOR/D the last bias from the calculated mixed IRS position can be used to give a good position. Basically the IRS will drift, by remembering by how much compared to known position (bias) it can give you a good position until the radio update is done.

Obviously for modern aircraft with full avionics.

[tom775257]

Perhaps to simplify further:

Simple aircraft: Sometimes fly a VOR radial, then perhaps you want to fly a track. So you would use a VOR receiver to fly a radial then a wind corrected heading to get a track. You know where you are, not the aircraft.

Complex aircraft: Aircraft tells you where you are. The aircraft does many things in the background to tell you where you are with the greatest accuracy possible. (You should always know where you are too). The aircraft will tune radio aids in the background to help tell you know where you as accurately as possible. The radio position in secondary to your computer produced position.

[WallyWumpus]

737NG FMC: Primary source of navigation is DME cross-cut. GPS and INS are both secondary.

[Denti]

@Wally: not according to boeing. An excerpt from our FCOM:

FMC logic selects the position from one of the GPS sensor units as the primary update to the FMC position. When GPS position data is available, radio updating can also occur. If all GPS data becomes unavailable, the FMC position will be determined by radio or inertial (IRS) updating.

New procedures like RNP AR approaches actually require us to disable VOR/VOR updating.

[ShyTorque]

The type I fly doesn't have an autotune facilty (single pilot. IFR heli). Having previously flown other types that do this, I wish this one did, too.

In transit I always manually tune in the most suitable VOR and DME (NDB, too) as a backup to the twin GPSs, irrespective of whether I'm flying under IFR or VFR.

[LikeABoss]

Thanks for the replies guys, but still I seem to be missing something here.

Firstly, we aren't flying radials anymore while enroute, which means the VOR is not being in use. Also, I understand that it's said to be used as a backup, but how is it backup exactly?
It will tell you where your position is (what radial you are on) from a certain VOR, and then how does that help you exactly?

Still seem to be a little confused.

[500 above]

Boss

Basically, if the GPS's and or other LRNS fail, the 'radio position' (as mentioned calculated by DME/DME, DME/VOR and so on etc) the FMS's still have a position based on the ground based navaids. You don't have to revert to beacon bashing, WPT to WPT is still possible.

[FE Hoppy]

The problem with this thread is that it's skipped navigation 1-9 and jumped straight in at chapter 10 RNAV.

For the OP you should start at the begining with basicnavigation then radio navigation and then research how things developed towards todays Area Navigation systems. This will give you a better feeling for the how's and why's.

[Piltdown Man]

The auto-tuning is often installed to enable the FMS to determine it's position, it's not necessarily for your use. So even when flying point-to-point using GPS, your "Plan B" is running in the background. Your plan should give you the ability to immediately know where you are, if you don't already know, following FMS failure. A radial and DME plus a chart is all you'll need to determine your position. And your position determines things like MSA, airspace limitations, local rules & procedures etc.

PM

[aterpster]

WallyWumpus:

737NG FMC: Primary source of navigation is DME cross-cut. GPS and INS are both secondary

That would create a problem in the U.S. Every RNAV IAP states "DME/DME RNP 0.30 not authorized."

Further, every RNAV SID and STAR must be evaluated for critical DME updating for the old, pre-GPS birds. If there is critical DME then the SID or STAR is not authorized for non-GPS platforms when that critical DME is inoperative.

The pecking order of all modern air carrier and high-end biz jet FMS navigators is:

GPS
Blended IRU position
DME/DME
VOR/DME
VOR/VOR

Further, to fly most RNAV procedures, only GPS is required; IRUs, DME/DME, VOR/DME, and VOR/VOR are not required, in fact, except for IRU(s) not authorized, to use the procedures.

In the case of RNP AR at least one IRU is required in addition to two GPSes and two FMSes. The exception is RNP AR of not less than 0.30 in any segment to be flown and RNP of less than 1.0 is not required for the missed approach. In that case, no IRU is required.

[FE Hoppy]

That would create a problem in the U.S. Every RNAV IAP states "DME/DME RNP 0.30 not authorized."

Further, every RNAV SID and STAR must be evaluated for critical DME updating for the old, pre-GPS birds. If there is critical DME then the SID or STAR is not authorized for non-GPS platforms when that critical DME is inoperative.

The pecking order of all modern air carrier and high-end biz jet FMS navigators is:

GPS
Blended IRU position
DME/DME
VOR/DME
VOR/VOR

Further, to fly most RNAV procedures, only GPS is required; IRUs, DME/DME, VOR/DME, and VOR/VOR are not required, in fact, except for IRU(s) not authorized, to use the procedures.

In the case of RNP AR at least one IRU is required in addition to two GPSes and two FMSes. The exception is RNP AR of not less than 0.30 in any segment to be flown and RNP of less than 1.0 is not required for the missed approach. In that case, no IRU is required.

Not exatly true in all cases.
For example the Primus Epic system goes:
Blended GPS
single GPS
then whoever has the lowest EPU from:
DME/DME
VOR/DME
IRS.


PBN specifications don't match the descriptions you give. For example RNAV 1 can be GPS or DME/DME or DME/DME/IRS. Each state can declare which is acceptable. If DME/DME or DME/DME/IRS only then the critical DME assesment is required. If GPS then the older equipment won't be RNAV 1 certified.

In China for RNAV 1 arrivals and departures it's a requirement to inhibit VOR/DME fixing as it doesn't meet RNAV 1 specifications.

[wiggy]

Hoppy

The problem with this thread is that it's skipped navigation 1-9 and jumped straight in at chapter 10 RNAV.


:ok:

To the OP:

You are going to be flying the magnetic tracks given in your flight plan to your way points, but why do you need the VORs tuned?



Difficult to answer without knowing how your aircraft is equipped. If it's a basic "radio nav only" (no FMC/IRU/even no FMC) are you going to rely solely on a magnetic track to get from A to B - no cross check?

With the relevant VOR tuned up and displayed you've got a basic way of knowing where in the world you are (airmanship/MFSmanship?;)), and a way of monitoring the tracking.

Indeed, once upon a time, before the days of RNAV some of us used to teach radio aids nav and the skill of flying to a radio defined waypoint directly without tracking in or out on a radial....well sometimes it worked:rolleyes:

[misd-agin]

Maybe the easiest answer to "how important" is - 'not much'.

Read reply #11. If you get down to VOR/VOR updating, which I don't think I've ever(?) seen 12,500+ hrs of 'PFM' operation, you'll probably have gone through a couple of checkslists that probably will tell you to ensure that VOR updating is in the 'auto', 'on' or 'enabled' mode.

PFM? Pure F***ing Magic. :D

It's a DFW system. DFW? Don't F*** With it. :ok:

[misd-agin]

wiggy - nothing like going direct to an intersect using the tail of the RMDI needles to figure out a direct course. RMDI triangulation = poor man's RNAV/LNAV. Going from RNAV capable a/c back to that in a military fighter, pre INS days, was a difficult regression. :ooh:

The auto updating function of the VOR has nothing to do with helping keep track of your location from a pilot's perspective. It rarely uses the VOR's that you're overflying. Instead it uses whatever it likes, which is typically offset from your route of flight.

[aterpster]

FE Hoppy:

PBN specifications don't match the descriptions you give. For example RNAV 1 can be GPS or DME/DME or DME/DME/IRS. Each state can declare which is acceptable. If DME/DME or DME/DME/IRS only then the critical DME assesment is required. If GPS then the older equipment won't be RNAV 1 certified.

I don't believe I said to the contrary for SIDs and STARs in the U.S.

Indeed, I stated the hierarchy incorrectly:

Dual GPS
GPS
Blended IRU updated by GPS (dual GPS for RNP AR IAPs)
DME/DME (must be excluded for RNP AR)
VOR/DME (must be excluded for RNP AR)
VOR/VOR (must be excluded for RNP AR)

There are additional requirements for RNP AR, depending upon the RNP value RNP 0.30 to as low as RNP 0.10:

Dual FMS
TWAS

and, other inputs that are beyond my domain.:)

[SFI145]

OK 465
I bet that you made you feel very good.
Thank goodness we have progressed from the 'trapper' mentality.

[Bite OK]

flying over soviet union countries on our 15 years A320 pre- GPS , during flight loosing our NAVAIDS (DME,VOR) for time to time, on destination we where of track by 5-10 nm , so without a continuose update from NAVAIDS accuracy of our ADIRS where getting lower,

just add on in previouse replys

[misd-agin]

UPT days. Final check ride included a 'point to point' for the high altitude penetration(military version of a STAR). Depending upon what area you had done your airwork in the entry into holding varied. Guys would really be sweating this.

I told a group discussing the various possibilities - "deliberately miss by a couple of miles to get into the sector you prefer, update as you get closer, you'll be in a turn hitting the fix and you just continue the entry into holding."

Guy looks at me - "I'm trying to find the GD fix and you're talking about deliberately missing it?!?!"