HiAs you may know, Flightaware.com has flight plans printed. I found this flightplan for KIAH-KSFOKIAHOrigin Airport29.9844336-95.3414422 WLLISReporting Point30.5346389-95.6516389 LOAVOR-TAC (NAVAID)31.1240278-95.9679444 ARTCC Boundary Crossing31.4284722-96.0860556 DOLEYReporting Point32.1891667-96.3847222 FUZVOR-TAC (NAVAID)32.8894444-97.1794167 SPSVOR-TAC (NAVAID)33.9872875-98.5934719 SONYAReporting Point34.2444722-99.5904722 TCCVOR-TAC (NAVAID)35.1821392-103.5985181 FTIVOR-TAC (NAVAID)35.6575708-105.1355889 FTIVOR-TAC (NAVAID)35.6575708-105.1355889 ESPANReporting Point36.1198194-106.3570389 RGINAReporting Point36.4630000-107.2960389 RSKVOR-TAC (NAVAID)36.7483928-108.0988992 RSKVOR-TAC (NAVAID)36.7483928-108.0988992 MLFVOR-TAC (NAVAID)38.3603556-113.0132328 MLFVOR-TAC (NAVAID)38.3603556-113.0132328 ILCVOR-TAC (NAVAID)38.2501928-114.3942264 OALVOR-TAC (NAVAID)38.0032614-117.7704458 KSFODestination Airport37.6189722-122.3748889Does this mean that airliners use VOR's for navaids? How do airliners navigate? GPS direct?

Aircraft use all sorts of navigation aids (VORs, DME, NDBs, GPS, WAAS) and SIDs, airways, STARs, andILS, to construct a flight plan.See the FAA's Instrument Flying Handbook and especially the Instrument Procedures Handbook, Ch. 3 "En-Route Operations".Cheers,- jahman.

I think as a rule aircraft on IFR flight plans will follow the airway system, and most airways are built from VORs. I know there are some RNAV airways in the US (I've ridden in the back of SWA flights that take one that goes direct from New Orleans to Tampa, in the past you had to go via Seminole VOR on a dog-leg). While you might be following an airway built on VORs, that doesn't mean you have to use VOR as your primary navigation device.scott s..

Regardless of what navaids are defining the actual flight plan, most commercial jets are using the GPS to navigate along the filed route. Like Scott said, even though the entire route may be built using victor/jet airways defined by VORs, the aircraft will use the GPS to follow the route. There are some flight plans that do use mostly GPS-based waypoints and even waypoints based on the lat/long lines found on the enroute charts. Here's and example:KORD ACITO ADELL ARLYN KK54K KK45I FSM BYP5This is the standard route for all of AA's ORD to DFW flights. ACITO, ADELL and ARLYN are just GPS waypoints created in space to streamline the departures out of KORD and KK54K and KK45I are actually taken from the grid lines on the high altitude enroute charts. If you want to see these waypoints go to skyvector.com and check out the H-5 Enroute chart and, for example, just to the east of KSTL and north of ALN you'll see KK54K.

ACITO, ADELL and ARLYN are just GPS waypoints created in space

That's incorrect. A waypoint has lat and lon coordinates independent of the navigational technique used to reach the waypoint.You may fly to a waypoint's coordinates via GPS, or as used to be the case via Inertial Navigation, LORAN and OMEGA and even VOR/DME or VOR/VOR.Note all waypoints have lat/long coordinates, but some waypoints also have radio beacon bearing and range.Remember FMCs existed for many years before GPS was even invented.Cheers,- jahman.

I don't disagree with what you say. My choice of wording may have been poor but what I was getting at was that the waypoints where just created at a particular point in "space" to accommodate the departures on the ORD5 SID. I never meant to imply that those waypoints don't have lat/long coordinates associated with them. You can clearly see on the ORD5 SID that they (coordinates) are published directly below the waypoint name.I was only trying to make the point that not every waypoint along a filed route necessarily corresponds to a VOR, intersection of VOR radials, DME fix, associated with an airway, etc. etc. In this case, somebody somewhere just took a specific location without reference to any other ground based navigational aids (using lat/longs, of course) and assigned a name to it to accommodate the spacing of traffic out of KORD.

From what I understand an airliner like Boeing tunes into VOR's within range automatically to keep its IRS system aligned using triangulation.

From what I understand an airliner like Boeing tunes into VOR's within range automatically to keep its IRS system aligned using triangulation.

This is a bit more complicated. There is a algorithm (part of FMS) that ranks different navigation sources and based on that it computes position. I think in a modern jet the first priority is given to data coming from GPS and then VOR/DME follows.

From what I understand an airliner like Boeing tunes into VOR's within range automatically to keep its IRS system aligned using triangulation.

That would be a very inaccurate system when further away from VORs. At 60 miles away one 1° radial is 1 mile wide. VOR receivers are allowed to be up to 6° off during flight so that means that with triangulation you can be up to 12 miles off course. Ring laser gyroscopes are much more accurate and don't need constant updates because of virtually no drift.

So what would be an accurate way to simulate a real flight without an FMC, say, with the default 737? Just plan a VOR to VOR flight at FL330 and leapfrog VORs all the way until your destination? How do u make the VOR waypoints show up on GPS then? From the VOR's how do you transition to an ILS landing?

Here is a terminology matter I am uncertain on, but will give it a shot: There is reference made to "navigation fixes" and "waypoints". A navigation fix is a position that is determined by visual reference, or reference to conventional navaids, such as on-top a VOR or visual feature, the intersection of two VOR radials, the intersection of a radial or localizer and a DME arc, etc. A "waypoint" is a position that is defined in terms of lat and long. Since the adoption of computerized navigation databases, it has been the practice of the industry to enter navigation fixes into the databases as waypoints with lat/long definitions. Aviation authorities have been helping this process by publishing official lat/long positions, was well as generating 5-letter names for navigation fixes. Chart symbology typically depicts fixes as triangles and waypoints as diamonds, also providing symbology for "fly-by" and "fly-over" waypoints.scott s..

That would be a very inaccurate system when further away from VORs. At 60 miles away one 1° radial is 1 mile wide. VOR receivers are allowed to be up to 6° off during flight so that means that with triangulation you can be up to 12 miles off course. Ring laser gyroscopes are much more accurate and don't need constant updates because of virtually no drift.

Gyros (of all kinds) only provide a reference frame for attitude information. You also need three accelerometers to integrate acceleration into speed (and then into distance) for inertial navigation and accelerometers introduce errors of their own. Ring laser gyros also have drift due to temperature variations and require noise to dither the signal to avoid drifting due to signal sticking (due to quantum effects the recombined laser signals want to remain in phase fo small changes in attitude that therefore go unregistered).Cheers,- jahman.

That would be a very inaccurate system when further away from VORs. At 60 miles away one 1° radial is 1 mile wide. VOR receivers are allowed to be up to 6° off during flight so that means that with triangulation you can be up to 12 miles off course. Ring laser gyroscopes are much more accurate and don't need constant updates because of virtually no drift.

Most FMCs I'm familiar with triangulate from DME/DME instead of radials.

Most FMCs I'm familiar with triangulate from DME/DME instead of radials.

How does that work exactly? You could be at a couple different places if it was only based off of DME.

How does that work exactly? You could be at a couple different places if it was only based off of DME.

If the FMS didn't know anything else, DME/DME will give two possible positions. However, I input a starting location into the box during preflight, so it has an idea of which of the two should be correct. And from there, it continues to use the solution which is closest to where it thinks it should be. If GPS fails, DME/DME is next in line, followed by VOR/DME, and finally its own Ded Reckoning for position.