VOR freq interference above FL450?

[Snow]

Hey I read somewhere that above FL450 is direct flight only (ie no jetways) because above that altutude you start to pick up more than one VOR on the same freq because of your height (as in the higher you go the more stuff you can pick up), but another book says that above FL450 vor range decreases from 130nm to 100nm which goes against the first point, anyone know which is correct or anyone actually been above FL450 here?

Thanks...

[A300Capt]

I don't know of anybody capable of flight at FL450 or above that uses VOR for navigation. Most, if not all, use GPS, INS, IRS or a combination thereof.

[Ophir]

GPS, Immigration and Naturalization Service and Internal Revenue Service? Are these guys wealthy but imigrants who are refusing to pay their taxes?

[pilot602]

I know GPS and INS ... is IRS just a variation of INS? Or, in other words, what is IRS?

[A300Capt]

[ QUOTE ]
what is IRS?

[/ QUOTE ]

Inerial Reference System. Basically, an upgraded INS using ring laser gyros. It's like the difference between an analog unit and a new digital unit. The IRS has no moving parts and low power requirements.

From a company flight manual:

[ QUOTE ]
The ring laser gyro is a triangle shaped device with a silicone body and a gas filled cavity. A cathode and two anodes are used to excite the gas and produce two laser beams travelling in opposite directions. Reflectors in each corner are used to reflect the lasers around the unit's body.

If the two laser beams travel the same distance, there will be no change in their frequency. However, if the unit is moved (accelerated), one light beam will travel a greater distance to the detector than the other beam. The beam travelling the greater distance will have a lower frequency than the beam travelling the shorter distance. The detector analyzes these frequency changes and sends the information to the computer, which then translates the data into movement in space.


By using three ring laser gyros and three accelerometers placed at right angles, it is possible to interpret all movement of the aircraft in space.


[/ QUOTE ]

[pilot602]

Cool. Thanks.

[Doug Taylor]

We have IRS on the -88's and -90's that uses multi-DME recievers to correct for drift.

Real jets usually have it crosschecked with GPS!

[seagull]

Actually, the IRS is just the inertial portion of the mix, just a term for the combination of IRUs which are
the individual units. The FMC uses IRS as the primary nav, but can update it with outside
sources. The MD-11 uses IRS inputs, updated by 2 GNS (GPS), plus 6 independent VOR/DME
receivers and it also updates with ILS and a position update from the database on the takeoff
runway position (latter doesn't happen with GNS updates).

[Snow]

Ok I already knew airliners didn't use VORs for primary navagation but the jetway you use are pretty much VOR to VOR weither you use VOR as navagation or not.

How about you coperate pilots you guys know why there are no jetways above FL450 or if the VOR range increases or decreases?

Thanks

[NJA_Capt]

[ QUOTE ]
How about you coperate pilots you guys know why there are no jetways above FL450 or if the VOR range increases or decreases?

[/ QUOTE ]
It's just the way the airways structure was set up. I guess the answer is "just because."

The second part of your question is rather moot. Above FL450 no-one is using VOR to VOR navigation. Not many people are up there anyway. I know when I'm up there, the last thing on my mind is whether the VOR range increased or decreased. It is either in range or it's not. Our primary nav is dual GPS. Followed by dual IRS(IV), then dual VOR/DME.

You can be cleared direct to a VOR 2000nm away, but you are using GPS/RNAV coordinates for the station as opposed to VOR reception. VORs are considered "short range" navigation.

[C650CPT]

I agree with the captain
One thing about corporate aircraft, most if not all are equiped with GPS. We even had GPS on the helicopter I used to fly.

I am absolutely amazed if not dissapointed by the commerciall airliners haveing to ask for headings until receiving the VOR that they've just been cleared to. I would think that the expense of a GPS would be nullified by the fuel airliners could save flying direct to legs.

[ananoman]

To the original point about VOR range. The service volume you are given is in 'steps', but it is better to think of it as a sphere. Service volume first increases then decreases with altitude. There are enough frequencies that interference should not be a problem. NDBs are another matter and interference can be a problem at night and at high altitude.