Definition
A published low altitude IFR airway designed to be flown using area navigation (RNAV) equipment rather than ground-based navigation aids. These routes appear on IFR En Route Low Altitude Charts and are identified with a 'T' prefix (T-routes), and they require the aircraft to have approved RNAV capability — typically GPS — to fly them.
Plain English
An IFR low-altitude route that you can only fly if your aircraft has approved GPS or other area navigation equipment, because it isn't built around traditional ground stations like VORs.
Context Anchor
Seen on IFR En Route Low Altitude charts when selecting, filing, or accepting an instrument route clearance.
Derivation
RNAV' stands for area navigation — a method of flying directly between any two points rather than from one ground station to the next. 'Low altitude' refers to the airspace structure below 18,000 feet MSL where these routes live. 'Only' is the key word: the route exists only for RNAV-equipped aircraft.
Why Pilots Care
Using one without the required equipment places the flight outside approved routing and can affect separation or clearance validity.
Intuition Check
“Low altitude” does not mean barely above the ground; here it means the low-altitude instrument route system, generally below 18,000 feet mean sea level. “RNAV only” does not mean any direct route you want; it means the published route requires approved area navigation equipment.
Example Sentence 1
She filed the T-route from KBED to KPVD because her certified GPS made the low altitude RNAV only route the most direct option.
Example Sentence 2
ATC issued a clearance via the low altitude RNAV only route because the aircraft had the proper equipment.