View Full Version : VOR tracking at 767

17th May 2002, 10:35
Could anybody spread some lights for limitations of autopilot VOR tracking at B767, I've heard that it only allowed for tracking (ILS) localizer only and if you require track VOR radial you should use FMC (put NAVAID ID / required radial ) or make it manually via HDG SEL following to HSI or RMI indications, in other words there isn't capabilty to tracking VOR by autopilot using both NAV VHF receiver, does it really true??

Thanks in advance

Mister Slot
17th May 2002, 12:18

17th May 2002, 12:40
Thanks Mr.Slot for input and nice and full explanation of the matter ;)

But anyway I'm really surprised with that.

18th May 2002, 03:32
Ruslan, I suppose you'll be just as shocked to learn that B757/767s and the Airbus products don't even have magnetic compass systems? :eek:

Why would you want to use old inaccurate radio coupling when you have a nice accurate FMS? Constant updating of the inertial position with Rho-Rho calculations based on DME seemed like magic back in the eighties when the B767's FMS was conceived, but now even that is old hat with GPS giving even greater accuracy.

Lets face it, Oboe and Gee did a pretty good job in their day, so did Decca too, but VOR became the standard. Now its time to put the beacons to rest and get on with the twenty first century. Area Nav and Free Flight - now thats the way to go! ;)

Through difficulties to the cinema

18th May 2002, 14:48
Mr Boeing says nyet to VOR tracking. Also no speed protection in VS mode.
Ironically you have to check your position frequently using the only source of "real" data available.

19th May 2002, 16:03
Well, thanks guys for follows up.

Iíve heard when States have been started their actions at Afghanistan and against Iraq a few ago GPS for area was unavailable for approx 6 hours. And I believe that bush flying pilot in Africa will rather prefer GPS, but not in case he has meet special task to find mobile/unpublished beacon (no LAT/LON at all) or some kind of military unpublished facility.

Bally Heck
19th May 2002, 19:17
No VOR tracking on 76/767 which increases pilot workload on VOR approaches, which is already rather high. Area navigation (IRS is not permitted for final approach, nor is it accurate enough)

20th May 2002, 03:21
Correct Bally, they're only certified for Area Navigation to RNP5 as delivered. New regs in the pipeline will bring in RNP1/3 within Eurocontrol before much longer, but it is noteworthy that in some countries, ATC already offer what they call 'Precision' RNav approaches - at Frankfurt for example - even though there are hardly any aircraft certified to better than RNP5.

And don't forget there are moves afoot to shut down existing VOR stations progressively, in the USA as well as other parts of the world. There is a tendency for ATC to move faster than the operating industry these days and Eurocontrol in particular doesn't care whether the technology is available on the aircraft or not - look at 8.33KHz Comms, RVSM, RNP5 and so on. Not to mention the US congressional mandate of a non-existant TCAS.
No, VOR is going the way of Terranosaurus Rex and Mr. Sperry's Flux Gate I'm afraid, so we'd better get used to the idea...

Ruslan, the US may have used 'Selective Denial' in Afghanistan but in a war zone VOR wouldn't be left running without intervention either. That's why military 'heavies' tend to carry the much mocked human navigator. ;)

Through difficulties to the cinema

20th May 2002, 14:58

CLANG! You'll be pleased to know that Airbuses (well, A320/321 anyway) have a particularly nice E2-B magnetic compass which pulls down from a housing above the windshield if required. Though how the farg you're supposed to fly by it and what catastrophe would have to lead to its use don't bear thinking about.

22nd May 2002, 04:20
The Boeings and just about everything else have a standby magnetic compass, fokker.

What I refer to is the lack of a magnetic compass SYSTEM. There are no flux detectors or compass couplers in the glass cockpit Boeings, nor I suppose in the fly-by-wire Airbus machines either. The magnetic information on modern digital aircraft comes from the INS/FMS. Mag is calculated from True by a using a magnetic variation database contained, on the Boeings anyway, within the IRU and which provides the magnetic variation for any position between latitudes 80N and 80S. Above those latitudes you only use True. The database is updated periodically by software updates.

VOR beacons are aligned to magnetic north, and radials are flown using magnetic headings, these are now commonly derived from True headings by software computations; Although radio coupling to VOR radials is not particularly accurate, the problem as identified by previous posts, is that sometimes only a VOR approach is available and if you can't auto-couple the autopilot, the workload is increased.

My point is that its about time to kill off dinosaur equipment like the VORs and catch up to the technology. Although INS and FMS were too expensive for light aircraft, nearly everyone can afford GPS based navigation systems these days. While the regulatory authorities remain well ahead of aeroplane equipment in some areas, they continue to lag behind in others - there should be some consistancy in application. Roll on GNSS/EGNOS and the twenty first century...

Through difficulties to the cinema

Bally Heck
22nd May 2002, 15:27
I think the main problem with GPS approaches is a political one. Once all terestrial aids are decommisioned, the "owner" of the satellites has a very powerful foreign policy weapon. This is why the USA is accepting and promoting GPS, but Europe and most of the rest of the world are wary. Governments will of course not publicly admit to this.

I believe Europe is soon to launch it's own satellites. This should see a wider acceptance of GPS approaches

Pilot Pete
22nd May 2002, 20:18
As pointed out by wickerman we always cross check the accuracy of the INS's by reference to a suitable VOR before trusting the accuracy of the map display.

This leads to the question that if and when VOR signals are turned off what reference are we going to cross check against? GPS? Not ground based either. At the moment I feel a lot happier checking the position against a known ground reference such as VOR.

Sure GPS is more accurate, but when it degrades it can surely not be used to cross check another system? What about microwave links? I understand that microwave approaches are already available so it would appear to me that ground based microwave signals would be the next step on from VOR.



ps Blacksheep, can you enlighten me as to GNSS/EGNOS? Not come accross the terms before.

22nd May 2002, 22:47
Just to digress a little, on the MD90 the standby compass is located BEHIND the pilots with a MIRROR in front of them. Iím not even going to ask how something like this could be certified!!!!


22nd May 2002, 23:58
It gets ceertified 'cause all MD series are like that and maybe the DC-9 as well I have no personal experience of that type.
Don't see the problem as long as I do my job and make sure the glass is clean.

23rd May 2002, 01:23
Inbound tracking of a radial is ok, but open-ended outbound tracking is not. Approaches coupled to the flight director in map mode are ok, but the other pilot must have VOR raw data displayed to ensure tracking performance. ADFs can be flown in the same way.

23rd May 2002, 05:00
Pilot Pete,

GNSS = Global Navigation Satellite System such as the American
GPS and the Russian GLONASS. Latest news on the on/off European Galileo system is that it's finally on but we don't know when yet.

EGNOS = European Geostationary Navigation Overlay System. An overlay that improves the accuracy of any of the geostationary satellite systems, enabling their use for Precision Area Navigation (PRNAV) In trials completed at Nice airport in September last year, EGNOS consistently provided precision guidance (within 30m horizontal and 40m vertical) on two complex fixed radius turns over 20nm to establish on a 2nm straight in final approach.

The concern over traffic congestion will eventually force the use of area navigation and precision curved approaches beyond the capability of micro-wave systems. Radio beacons have served us well but the days of aircraft streaming in long straight lines between radio stations cannot continue. There simply isn't enough room any more.

Through difficulties to the cinema

Pilot Pete
27th May 2002, 22:49

Very interesting, thanks for that.


29th May 2002, 07:09
US have just decided to keep VOR's for the forseeable, as GPS is too easy to jam. The signal is so feeble that anyone with a low powered device in the boot of his car could shut down a terminal area with ease. The RAF have conducted frequent GPS jamming trials involving large chunks of the UK(all on notams) with a great degree of success judging by the blank display on my GPS during one such test.
Not sure about 80N to 80S being useable for MAG headings on an IRS system btw. Its 73N to 60S according to my paperwork but maybe there is some upgrade .....I reckon I'd prefer to be in True no matter what if I was that far up(which I've never been so i cant possibly comment further)

31st May 2002, 02:59
The mag/var tables are from 80 to 80 but the practical limits for accurate navigation are 73N to 60S, sir.

Through difficulties to the cinema

22nd May 2003, 19:34
Blacksheep / fokker,

And the fmc variation database is only updated every 5 years, which means it is rarely correct !!

22nd May 2003, 19:54
I'm aware of the Boeing problem with tracking VORs through an overhead, but why can the 767 not track a radial in a/p?

Incidentally, DME should be used to check FMC position as well.

Silly old fashioned question if you are bored! You loose ALL instruments IMC at night, except the standby compass. On which heading should you descend to MSA?

22nd May 2003, 22:54
north or south I reckon ??
(no acceleration errors ?)

22nd May 2003, 23:34
Getting warm! (On the right 'track'):cool:

23rd May 2003, 02:16
A 357 day gap between Backsheeps post and expedite_climbs post. Is this a record?

23rd May 2003, 02:38
p22. How bizarre, particularly as I only use 'view posts since your last visit'. Could have sworn i was watching this topic a few days too....