On a low-altitude IFR chart, the T-airways (GPS) have (for the most part) an MAA of 15,000 feet. Why is this?

Question

I can't really seem to find a reason why the GPS-airways should have an MAA.

I've asked lots of instructors and fellow students, with no luck..

Basically it can't be because of jet airways, as they start at 18 000 at the very least, and the gps signal should be good a lot further up than just 15 000?

Answer 1

I follow your reasoning and MAA is usually either terrain or NAVAID reception driven.  Since the GPS reception is not masked by terrain (enroute), the sectional must have a bunch of terrain.  What's the MAA's on the nearby Vicotr routes?  It' might actually be higher if the terrain masked the VORTAC.

EDIT:  Hmmm, that's really strange.  It's got to be some sort of procedural deconfliction thing then.

Answer 2

I could very well be wrong about this, and if I am please correct me...but doesn't the "T" in T-Airway stand for "Terminal?"

That would mean that in order for that routing to vbe assigned, it would be given by a TRACON, rather than an ARTCC, as most IFR clearances are assigned.  The TRACON may simply have other traffic flying over those airways at higher altitudes (i.e. SIDs and STARS) and need to limit TEC traffic to lower altitudes than those the enroute traffic is using.

Terminal Enroute Clearances (TECs) are assigned by the local RADAR approach controller (TRACON) and do not require approval from Center controllers (ARTCC).  These routes are typically designed to keep you seperated from other IFR traffic, but since the clearance does not go through the ARTCC, it can be handed out with no knowledge of other IFR traffic.  For that reason, the routes and altitudes assigned to TEC clearances are different than those assigned to other IFR traffic.  It may well be that there is an agreement between whatever ATC facilities you are dealing with that they are allowed to assign altitudes only up to 15,000'.  That could be reflected on the Low Altitude chart as an MAA simply to avoid confusion.

Answer 3

. RNAV terminal transition routes, referred to as Tango or “T” routes, allow Global Positioning System (GPS) equipped, instrument flight rules (IFR) operations to efficiently fly around or through Class B and Class C airspace areas.

An additional Tango route was established in the Outer Banks, North Carolina, area to replace an airway that became unusable with the decommissioning of a supporting nondirectional beacon..

Answer 4

Here's a link about T-Routes. They are Area Navigation IFR Terminal Transition Routes:

http://www.aopa.org/whatsnew/newsitems/2...

Here's a link about "T" routes to Puerto Rico being redesignated as "Y" routes:

http://209.85.173.104/search?q=cache:UTc...

The "T" is for Terminal. That is the reason for the altitude limitation.

As for high altitude use of GPS on published area nav routes, check out the "Q" routes. Have flown them over the Gulf of Mexico at FL 390 and FL 400.

Answer 5

Where are you looking?  I looked at several low-altitude en-route charts and T airways are scarce, and the few I saw had no MAAs specified.