Upper airway vs. airway

[TafelLager]

Hi there

Hope someone can help on this one.

What is the difference between an upper and lower airway? I'm not talking about the airway altitude/ FL limits, I want to know why are they seperated and not just one airway? And if this info is in the Jeppesen, where can I find it? Been looking but can't find anything.

Cheers,
TL

[Superpilot]

An obvious one would be so that slower traffic doesn't get in the way of much faster traffic.

[126.9]

I don't recall there being any such thing as a LOWER airway. The prefix L would normally indicate a Low or Medium Frequency airway. Prefix U is normally associated with that portion of the airway which is RNAV. There are others too: G is for Flight Information Service only, DOM for domestic traffic, D for direst, V for victor or VHF, and then NAT, OTR, R and so on. The names can also have meaningful suffixes. Check out your Jeppesen Introduction section. This stuff used to be in the pages numbered fifty-something.

[parabellum]

Jeppesen issue specifically named High Level and Low Level charts.

I think Superpilot is close to the money, slow and/or unpressurised a/c in the lower levels. An ATCer will arrive shortly and put us all straight!

[galaxy flyer]

One difference is low altitude airways have a specified width, 4nm for the primary zone, either side of centerline for terrain clearance. Upper routes have no width because they do not need to be surveyed for terrain; they are merely the great circles between waypoints or navaids.

GF

[MarkerInbound]

You can run 400 knots at 12,000 if you can afford the fuel and some turbo props get into the middle 20s doing 250 knots so I don't think speed is a criteria.

The service volume of VORs jumps at 18,000 (in the US) and so a route that had to go from A to B to C at 17,000 can go A to C at 18.

[126.9]

parabellum

There is a clear difference between what he's talking about and what you're talking about. High level and low level charts are not the same as airways designated UPPER.

Checkout Jeppesen Airways Manual Introduction, page 57, or read my reply above again. Enough said!

[TafelLager]

Thanks guys.

Yes, I'm not taliking about high/ low enroute charts.

I had a look at those pages (57) and compared them to enroute charts. Some airways are designated for example UG854 which would mean according to 126.9's explanation and also what I found in the Jepp that it's an RNAV route....but, why then do you get routes that will be UM974R , with the "R" clearly indicating that it is an RNAV route. Wouldn't this be like saying the same thing twice?

Cheers,
TL

[126.9]

Yes, that would be like saying the same thing twice. That's why there is no such thing. Suffixes added to UPPER routes are only ever conditional route categories Eg: UG555R1. In order to determine what they mean, you have to consult the Enroute Listing. The RNAV suffix to which you refer is clearly for use on other airways with other naming constraints. Much like the example given on page 56 really: J888R - Jet Route 888 RNAV.

[Spitoon]

I think the fundamental reason is historic. The airway structure in the days of turbo-charged pistons and the like had a practical upper limit of about 25000 ft. When jets were introduced they could go faster and higher and upper routes were introduced to cater for their operations. And the distinction remains to this day.

Today the performance of propeller-driven aircraft is similar to some lower performance jet aircraft and the need for different route structures doesn't really exist in many areas. This is evident because upper and lower routes are coincident in many cases.

More recent innovations such as RNAV have probably been introduced within specific portions of upper or lower airspace as much as a convenience in many cases because there is already a distinction between these blocks of airspace.

[parabellum]

Checkout Jeppesen Airways Manual Introduction, page 57, or read my reply above again. Enough said!

I don't have access to Jeppesens these days but my point was that if there are High and Low level charts then it is not unreasonable to assume that there are High and Low level airways, for whatever reason.

Enough said.

[chevvron]

Not sure if this still applies but years ago, there were Airways and Upper Air ROUTES not airways. This was because below FL245 (now FL195), airways were established what is now called class G airspace, but above 245, all airspace was class A; nowadays all; airspace above 195 is class C with upper air routes running through it.
To put it in its simplest form, in the UK, airways are individual control areas, whereas upper air routes are defined routes through one huge control area.