Definition
The altitudes at which an aircraft flies during the en route portion of a flight, between the climb after departure and the descent before arrival. On en route low altitude charts, cruising altitude information is shown alongside airway data and is governed by regulatory rules that assign specific altitudes based on direction of flight and whether the aircraft is operating under VFR or IFR.
Plain English
The level-off heights a pilot uses for the main, steady part of a flight — after climbing up and before starting down. Rules tell pilots which altitudes they're allowed to use depending on which way they're heading and how they're flying.
Context Anchor
Seen in en route chart legends, flight planning, and instrument flight when choosing or following an altitude for the route segment.
Derivation
From 'cruise,' originally a nautical term meaning to sail steadily on a set course. Aviation borrowed it for the steady, level portion of a flight — so 'cruising altitude' is simply the altitude flown during that steady phase.
Why Pilots Care
Following the correct cruising altitude prevents mid-air collisions and keeps the flight legal under ATC and regulatory requirements.
Analogy
Think of cruising altitudes like lanes on a highway. Aircraft going different directions use different height “lanes” so they are less likely to meet head-on at the same level.
Intuition Check
Do not read “cruising” as casual or optional here. In this context, cruising altitudes are planned or assigned heights used during the en route part of flight.
Example Sentence 1
After leveling off at his cruising altitude of 7,000 feet, the pilot trimmed the aircraft and began monitoring fuel burn.
Example Sentence 2
On the en route chart the cruising altitudes legend showed that westbound VFR traffic should use even altitudes plus 500 feet.