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Does 777 Use VORs  
User currently offlineGopal From United States of America, joined Jun 1999, 113 posts, RR: 0
Posted (7 years 4 months 4 weeks 21 hours ago) and read 3027 times:

Does Boeing 777, being one of the most advanced airliners, still use VORs for navigation when flying between cities within the US ? Do other latest models such as A330-300 also VORs as well. When traversing oceanic routes, they use GPS systems, I think.

27 replies: All unread, showing first 25:
 
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 1, posted (7 years 4 months 4 weeks 20 hours ago) and read 3016 times:

On the "modern" aircraft, the primary means of navigation is via the FMS. The FMS includes the IRS/ADIRU, the FMC (flight management computers) and the FMSCDU, or the input device.

The FMC gets the aircraft's position from the IRS and then that is further refined by GPS updates as well as VOR/DME, ILS DME or VOR/VOR. The flight plans are filed, in domestic ops, using standard jet routes which include VORs. The FMS takes care of everything, but the pilot's don't select the VOR stations and then set the inbound course if that's what you're asking...

On international flights, the flight plan is loaded and the same procedure applies. The actual navigation is done by the FMC and it is updated via GPS (assuming it's available).
Hope that helps.

[Edited 2006-11-27 14:15:54]

User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 2, posted (7 years 4 months 4 weeks 20 hours ago) and read 3013 times:

The CRJ FMS works as you've described, Philsquares, but interestingly enough, when you look at how the FMS updates IRS position, GPS is at the bottom of the list, after DMEs and VORs.

User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 3, posted (7 years 4 months 4 weeks 20 hours ago) and read 3021 times:

Quoting Avt007 (Reply 2):
The CRJ FMS works as you've described, Philsquares, but interestingly enough, when you look at how the FMS updates IRS position, GPS is at the bottom of the list, after DMEs and VORs.

On all the Boeings, and IIRC the Airbus, the first choice is GPS, then if that's not available, it looks for ILS DME/ ILS DME, VORDME/VORDME then VOR/VORDME then finally VOR/VOR. If it can't up date then the FMC then uses it's know error rate to compute the triplemix position.

Plus I don't know about the CRJ, but you can never up date the IRS position, you can only update the FMC position.


User currently offlineDeltaGuy From , joined Dec 1969, posts, RR:
Reply 4, posted (7 years 4 months 4 weeks 18 hours ago) and read 2978 times:

If you go to the PROG page on many FMS's, you can see the VOR's that it's cross referencing to maintain it's proper position. Sometimes there are several in there.

DeltaGuy


User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 5, posted (7 years 4 months 4 weeks 18 hours ago) and read 2969 times:

You're right Phil, the priority is, IIRC, multi DME, DME/DME, DME with colocated VOR, IRS, GPS. This list is for updating the FMS position, not the IRS as I said.

User currently offlineXXXX10 From United Kingdom, joined Jan 2000, 777 posts, RR: 0
Reply 6, posted (7 years 4 months 4 weeks 18 hours ago) and read 2959 times:

Sorry for being slightly off topic here but could a modern aircraft (777, A330. 738 etc) be dispatched without a working FMS system-assuming that it was only flying over areas with good VOR coverage.

User currently offlineTristarSteve From Sweden, joined Nov 2005, 3934 posts, RR: 34
Reply 7, posted (7 years 4 months 4 weeks 17 hours ago) and read 2931 times:

Quoting XXXX10 (Reply 6):
Sorry for being slightly off topic here but could a modern aircraft (777, A330. 738 etc) be dispatched without a working FMS system-assuming that it was only flying over areas with good VOR coverage.

No.
The B777 has two FMCS. One must be serviceable for dispatch, and both serviceable for FANS routes.
The A320 has two FMGCs Flight Management Guidance Computors. These are a combined FMS and AP control system. One whole system must be serviceable.
But go back to the B737-400. Ours have a single FMS and this is acceptable inoperative.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 3934 posts, RR: 34
Reply 8, posted (7 years 4 months 4 weeks 17 hours ago) and read 2924 times:

Quoting PhilSquares (Reply 3):
On all the Boeings, and IIRC the Airbus, the first choice is GPS



Quoting Avt007 (Reply 5):
You're right Phil, the priority is, IIRC, multi DME, DME/DME, DME with colocated VOR, IRS, GPS

I agree with Avt007. The most accurate position is with DMEs and the FMS will take these first if available.
In fact for non-ETOPS A320 I wonder sometimes why we have three INS and two GPS. Seems a bit of an overkill when a single auto-tune DME is all you need!
In the good old days of the B737-200 we flew ARN-LHR over DANDI in the North sea, and with no IRS were on dead reckoning for 20 mins. I think you guys are spoiled nowadays.


User currently offlineGopal From United States of America, joined Jun 1999, 113 posts, RR: 0
Reply 9, posted (7 years 4 months 4 weeks 16 hours ago) and read 2908 times:

Thank you, everyone for the informative replies. How long does it take for a pilot to gain mastery over the FMS ? Does is require in-dept knowledge if IRS and INS ?

User currently offlineDalb777 From United States of America, joined May 2005, 2192 posts, RR: 0
Reply 10, posted (7 years 4 months 4 weeks 16 hours ago) and read 2892 times:

Can someone explain what IRS and INS are?


Geaux Tigers! Geaux Hornets! Geaux Saints! WHO DAT!!!
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 11, posted (7 years 4 months 4 weeks 14 hours ago) and read 2835 times:

Quoting Dalb777 (Reply 10):
Can someone explain what IRS and INS are?

Inertial Navigation System...vs. Inertial Reference System. In the "old" days the INS would navigate. Today, the IRS feeds inputs into the FMC and the FMC navigates.


User currently offlineSlamClick From United States of America, joined Nov 2003, 10062 posts, RR: 68
Reply 12, posted (7 years 4 months 4 weeks 13 hours ago) and read 2830 times:

IRS is inertial Reference system.
INS is inertial Navigation system.

If I'm not mistaken the Reference is the newer, updated version.

The "inertial" part of the system uses extremely sensitive and accurate accelerometers and ring-laser-gyros to sense movement in all three axes.

The "reference" means that it uses other elements to confirm, refine and present the navigation and flight data. These may include GPS or DME/DME and even manual position updating to correct as you go.

So you are sitting on the ramp, about to power the system up. Your company Jepp chart has the latitude/longitude to a tenth of a minute of arc for the very gate you are parked at. You enter that into the system and start it up.

The system goes through some self-checking. Among the things it does in this phase is find local vertical and measure the rotation of the earth. It uses this to find north - possibly confirmed with a fluxgate compass. It compares the earth's rotational speed with the latitude as a validity check for present initial position. It may also check the initial position against the stored position when it was shut down. If they differ by more than a couple of miles it may ask the pilot to confirm the new position. If a catering truck pulls up to 1R door and bumps the airplane at this time it could fail its initial checks.

Before moving the airplane, the flightplan will be input to the flight management computer. Not so long ago you had to input the forecast winds along your route of flight. Those may well come via ACARS now which saves many keystrokes.

When the airplane begins to move, the airplane notes that movement. It does by two methods - the little accelerometers and RLGs and also by the changing of "present position" as determined by GPS or DME/DME readings.

The system provides not only navigation but flight information including the artificial horizon which it derives from knowing UP. It also gives vertical speed and compass heading among other things.

So when you are underway, by its movement-sensing it knows how fast you are actually going and it what actual direction over the ground. It will compare the compass heading and the true airspeed from the air data computers with the actual direction and speed of travel. The difference between these is the wind factor, both wind direction and speed can be determined from these - in realtime.

We fly along with the VOR receivers in an "auto" mode, allowing the system to tune VOR station along the route of flight. It will try to select two where the bearing to the station is as near as possible to 90 degrees from each other, and use those stations DME readings only to confirm or update present position. If you look at an enroute chart you can see that 102nm from this VOR and 86nm from that VOR occurs at two locations or cusps in the overlapping circles. Of course it knows which of those two would make sense from its last known position (about a tenth of a second ago  Smile) and it also had the radials so it never has an ambiguity problem.

If ATC clears us direct "Hector" for example, which is a VOR out in Southern California from which some LAX arrivals begin, they expect us to overfly Hector. Our plane will do that but it will navigate to the published lat/long of Hector without necessarily actually tuning it. We can just type HEC into the scratchpad and line select it onto the flight plan. (depending on the type of system)

Anyhow that is kind of an overview, the broad strokes on how a typical system might work. I've been trained on two different Boeing systems and two different Airbus system so individual features have all kind of run together. Sorry.

Questions?



Happiness is not seeing another trite Ste. Maarten photo all week long.
User currently offlineBoeingOnFinal From Norway, joined Apr 2006, 476 posts, RR: 0
Reply 13, posted (7 years 4 months 4 weeks 13 hours ago) and read 2814 times:

This is why you guys are on my respected users list, I learn so much valuable information. Starting to wonder if I should just stop reading the theory books and just ask you guys instead :p

Anywho, how is a point like HEC chosen? Do they have to VOR radials crossing at as close as 90 degrees, and put that as one navigation point into the FMS system?



norwegianpilot.blogspot.com
User currently offlineAvt007 From Canada, joined Jul 2000, 2132 posts, RR: 5
Reply 14, posted (7 years 4 months 4 weeks 13 hours ago) and read 2808 times:

Excellent description Slamclick. I'll add my two cents- IRS find true north, then using a database of magnetic variation for your location, it displays magnetic north. The one other thing it needs is longitude. Latitude it can figure out on it's own, but you have to enter longitude, then you are in business.

User currently offlineTristarsteve From Sweden, joined Nov 2005, 3934 posts, RR: 34
Reply 15, posted (7 years 4 months 4 weeks 12 hours ago) and read 2798 times:

Quoting BoeingOnFinal (Reply 13):
Anywho, how is a point like HEC chosen?

Most waypoints are the sites of VORs.
20 years ago they all were, but with the advent of FMC navigation on all airliners today, they can be situated anywhere. The FMC computor can work out where they are by doing the math.

By the way the math involved in an IRS system is all calculus. Remember that from school? The IRS measures acceleration, then integrates it to find speed, and integrates it again to find position. And you wondered why you learned integration!!


User currently offlineGoldenshield From United States of America, joined Jan 2001, 5845 posts, RR: 15
Reply 16, posted (7 years 4 months 4 weeks 11 hours ago) and read 2762 times:

Quoting TristarSteve (Reply 7):
Quoting XXXX10 (Reply 6):
Sorry for being slightly off topic here but could a modern aircraft (777, A330. 738 etc) be dispatched without a working FMS system-assuming that it was only flying over areas with good VOR coverage.

No.
The B777 has two FMCS. One must be serviceable for dispatch, and both serviceable for FANS routes.

That may be applicable in Europe, but here in the states, we have pretty good navaid coverage. If one were to go down along the intended route of flight, it will be rerouted using good navaids, and pilots will just have to manually tune the navaids, and then use the autopilot to follow the radials, or fly them manually.



Two all beef patties, special sauce, lettuce, cheese, pickles, onions on a sesame seed bun.
User currently offlineBond007 From United States of America, joined Mar 2005, 5349 posts, RR: 8
Reply 17, posted (7 years 4 months 4 weeks 11 hours ago) and read 2751 times:

Quoting Goldenshield (Reply 16):
it will be rerouted using good navaids, and pilots will just have to manually tune the navaids, and then use the autopilot to follow the radials, or fly them manually.

Good god man!

I'd need to get the old textbooks out  Smile

hmmm....Radials....navaids....aaahh, I see them now in the index.


Jimbo



I'd rather be on the ground wishing I was in the air, than in the air wishing I was on the ground!
User currently offlineDalb777 From United States of America, joined May 2005, 2192 posts, RR: 0
Reply 18, posted (7 years 4 months 4 weeks 10 hours ago) and read 2721 times:

Quoting SlamClick (Reply 12):

Wow, thanks so much for that explanation. I have always wondered how that system works.



Geaux Tigers! Geaux Hornets! Geaux Saints! WHO DAT!!!
User currently offlineIAHFLYR From United States of America, joined Jun 2005, 4790 posts, RR: 23
Reply 19, posted (7 years 4 months 4 weeks 10 hours ago) and read 2700 times:

Quoting PhilSquares (Reply 3):
On all the Boeings, and IIRC the Airbus, the first choice is GPS, then if that's not available, it looks for ILS DME/ ILS DME, VORDME/VORDME then VOR/VORDME then finally VOR/VOR

But doesn't the Honeywell and Smiths FMC's need to have the larger database to use the localizer DME's otherwise they are taken out of the NAV solution?

Quoting Avt007 (Reply 14):
Excellent description Slamclick

A very good description that even I the lowest common denomitor can slightly gasp!!



Any views shared are strictly my own and do not a represent those of any former employer.
User currently offlineBoeingOnFinal From Norway, joined Apr 2006, 476 posts, RR: 0
Reply 20, posted (7 years 4 months 4 weeks 10 hours ago) and read 2700 times:

Thank you Tristarsteve. So the IRS calculates points from the coordinates it currently "think is correct"?

And, how often does the IRS needs "updating"? The directional gyro needs updating every 15 minutes because of the earth rotation, so I guess the IRS gyros are affected by that as well?



norwegianpilot.blogspot.com
User currently offlineTimz From United States of America, joined Sep 1999, 6712 posts, RR: 7
Reply 21, posted (7 years 4 months 4 weeks 9 hours ago) and read 2696 times:

Quoting Tristarsteve (Reply 15):
Most waypoints are the sites of VORs.
20 years ago they all were ...

In 1986? There were named places on the charts, defined only by their lat-lons, weren't there? Say, along the California-to-Hawaii routes? You're saying those weren't "waypoints"?


User currently offlineMeister808 From United States of America, joined Jan 2000, 973 posts, RR: 1
Reply 22, posted (7 years 4 months 4 weeks 9 hours ago) and read 2684 times:

Quoting Timz (Reply 21):
In 1986?

20 years ago is getting newer and newer all the time...

-Meister



Twin Cessna 812 Victor, Minneapolis Center, we observe your operation in the immediate vicinity of extreme precipitation
User currently offlinePhilSquares From , joined Dec 1969, posts, RR:
Reply 23, posted (7 years 4 months 4 weeks 5 hours ago) and read 2629 times:

Quoting BoeingOnFinal (Reply 20):
And, how often does the IRS needs "updating"? The directional gyro needs updating every 15 minutes because of the earth rotation, so I guess the IRS gyros are affected by that as well?

Today"s IRSs are extremely accurate due to the lack of moving parts when you compare them with the first generation INS. But, once they're aligned and in flight, the only updating that goes on is the FMC position. On the 744 you can select POS and you'll get the input of the IRS on the ND. Sometimes they're real close, other time, you'll see one drifting away from the other two. Even that isn't unusual. The error induced by the IRS into the FMC is adjusted by the other external inputs, such as GPS/ILSDME, VORDME and VOR bearing. But again you can't update the IRS in flight only the FMC.

Quoting IAHFLYR (Reply 19):
But doesn't the Honeywell and Smiths FMC's need to have the larger database to use the localizer DME's otherwise they are taken out of the NAV solution?


The Nav database in the Honeywell system is large. There are several upgrades available to expand the memory if required. I've flown 774 who lacked the memory to have stored routes because of the lack of memory and conversely, at my company, just about every route we fly is stored with multiple routings to each destination.


User currently offlineTristarSteve From Sweden, joined Nov 2005, 3934 posts, RR: 34
Reply 24, posted (7 years 4 months 4 weeks 2 hours ago) and read 2605 times:

Quoting Goldenshield (Reply 16):
Quoting TristarSteve (Reply 7):
Quoting XXXX10 (Reply 6):
Sorry for being slightly off topic here but could a modern aircraft (777, A330. 738 etc) be dispatched without a working FMS system-assuming that it was only flying over areas with good VOR coverage.

No.
The B777 has two FMCS. One must be serviceable for dispatch, and both serviceable for FANS routes.

That may be applicable in Europe, but here in the states, we have pretty good navaid coverage. If one were to go down along the intended route of flight, it will be rerouted using good navaids, and pilots will just have to manually tune the navaids, and then use the autopilot to follow the radials, or fly them manually.

Sorry, I was quoting from the Boeing produced MEL. Perhaps your airline has amended it with agreement from Boeing so you can fly without an FMCS. But how do you tune the VORs? There are no control panel. Manual tuning is via the CDUs. These CDUs are also the only way to align the ADIRU.


25 Goldenshield : Sorry, my bad. You were talking about the panel itself, and not the actual flying without FMS.
26 SlamClick : I had questioned that statement myself but hadn't bothered to post. I wasn't flying in Europe in 1986 but I can assure you that here in the US the ma
27 Radelow : I have to echo the comments from some people here... You guys are awesome! Thanks for the easy to understand explanation of how this stuff works...alw
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