Definition
This entry is a fragment of a glossary heading, not a standalone aeronautical term. In the Aeronautical Information Manual glossary, 'Substitute Route' refers to a route assigned by ATC when the regular airway or navigation aid is unavailable, and the full heading describes how some of these substitute routes are depicted on en route low altitude charts (the 'U.S.' charts). The fragment 'Substitute Routes Which Are Shown on U' is the truncated start of that heading and has no independent operational meaning.
Plain English
This isn't a real term on its own — it's the cut-off start of a glossary heading about substitute routes shown on en route charts. The actual term to look up is 'Substitute Route.'
Context Anchor
Seen in the AIM glossary and in IFR route planning or ATC clearance situations when a normal route is unavailable.
Derivation
Substitute comes from Latin words meaning “to put in place of.” That fits the aviation meaning: this route is put in place of the normal route when the normal route cannot be used.
Why Pilots Care
Provides a pre-approved, charted way to continue the flight safely without creating a new route from scratch.
Intuition Check
“Substitute” does not mean a pilot may casually choose any different path. Here it means a recognized replacement route, shown on official charts, that can be assigned when the normal route is not usable.
Example Sentence 1
While reviewing the AIM glossary, the student noticed 'Substitute Routes Which Are Shown on U' was a cut-off heading and turned to the full 'Substitute Route' entry instead.
Example Sentence 2
The AIM notes that substitute routes which are shown on U.S. charts are valid alternatives during navigation outages.