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I have a little misunderstanding about the two concepts: Cruise and En-route. Could you guys help me to compare the similarities and differences between these two concepts, maybe in some aspect like air traffic controller or aircraft performance, flight mechanics, ... Its would be my pleasure to see some answer from you guys, thanks a lot.

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    $\begingroup$ Enroute and cruise are essentially the same thing. Why do you think they are different? $\endgroup$ Nov 5 '21 at 17:31
  • $\begingroup$ I think ''En-route'' is larger in meaning than ''Cruise''. Am I right ? But how about in air traffic control ? Did ATC used these two as one ? I normally heard they used cruise more often than ''en-route'' $\endgroup$ Nov 5 '21 at 17:40
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    $\begingroup$ “Cruise” implies a power setting. Most aircraft use “cruise” power to be “enroute”. Long range cruise, economy cruise, high speed cruise, etc. There might be some rare exceptions I suppose. $\endgroup$ Nov 5 '21 at 17:48
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    $\begingroup$ Where have you heard these terms? What is the context? $\endgroup$
    – GdD
    Nov 5 '21 at 17:48
  • $\begingroup$ Where have you heard these terms used? What is the context? $\endgroup$
    – GdD
    Nov 5 '21 at 17:49
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As others have said, the terms are mostly synonymous when referring to an aircraft's phase of flight, with the meaning "the aircraft has leveled off at their highest desired altitude." But as there are a few specific meanings:

  • Like @757toga mentioned, a cruise clearance is a clearance for an aircraft to fly at any appropriate altitude along their route toward their destination airport, and then execute any approach procedure at that airport. It is important to be aware of that terminology and not mistake another term for a "cruise clearance."

    • So it would be unlikely for a controller do describe an aircraft as "cruising" unless they had been issued a cruise clearance. Instead they would describe the traffic as "enroute at [altitude]" or "level at [altitude]."
  • FAA facilities are divided into Terminal (towers and low-altitude Terminal Radar Approach Controls) and Enroute (high-altitude Air Route Traffic Control Centers). The term "cruise facility" would never be substituted for "enroute facility."

    • In other countries low-altitude facilities are called terminal control and high-altitude facilities are called area control.
  • As @Mike mentioned, aircraft documents are more likely to refer to "cruise power setting" rather than "enroute power setting."

In general, you will need to be more specific about your context in order to see what exactly the terms mean and if there is any difference between them.

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    $\begingroup$ important to mention: Your first bullet point is only true for FAA-Land. The rest of the world doesn’t know a „cruise-clearance“ and would usually talk about aircraft „cruising at FLXXX“ or „requested cruise level“. $\endgroup$
    – pcfreakxx
    Nov 6 '21 at 21:02
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En-route, often written enroute has been always understood as the phase where the aircraft has completed the departure procedure and has not yet transitioned to the arrival procedure. During this phase aircraft are flying along "airways", medium and high altitude corridors where aircraft are "cruising", and are controlled by specific control centers.

But in order to make sure all countries and aviation organizations use the same wording, ICAO wanted to create a precise definition. The first goal was to have a common classification of incidents and accidents. ICAO enroute phase includes cruising:

Instrument Flight Rules (IFR): From completion of Initial Climb through cruise altitude and completion of controlled descent to the Initial Approach Fix (IAF).

Visual Flight Rules (VFR): From completion of Initial Climb through cruise and controlled descent to the VFR pattern altitude or 1,000 feet above runway elevation, whichever comes first.

Source: ICAO.
Anything using a wording like "whichever comes first" is to be taken for serious imho :-)

Enroute

Some more details:

This phase of flight includes the following subphases

  • Climb to Cruise: IFR: From completion of Initial Climb to arrival at initial assigned cruise altitude. VFR: From completion of Initial Climb to initial cruise altitude.
  • Cruise: Any level flight segment after arrival at initial cruise altitude until the start of descent to the destination.
  • Change of Cruise Level: Any climb or descent during cruise after the initial climb to cruise, but before descent to the destination.
  • Descent: IFR: Descent from cruise to either Initial Approach Fix (IAF) or VFR pattern entry. VFR: Descent from cruise to the VFR pattern entry or 1,000 feet above the runway elevation, whichever comes first.
  • Holding: Execution of a predetermined maneuver (usually an oval racetrack pattern) which keeps the aircraft within a specified airspace while awaiting further clearance. Descent during holding is also covered in this subphase.

Source: ICAO.

There are IFR Enroute Aeronautical Charts, used for the enroute phase of the flight, and there is an enroute control:

enter image description here

Source: What is a TRACON?

Cruise

Cruise is flying at a certain engine economical regime, when the goal is mostly to cover the distance to the destination. Other phases include complying with noise regulations, using safe paths in busy areas, climbing, descending. During these phases the aircraft is under-performing from fuel consumption and speed standpoints.

Engine and aircraft manufacturers give to cruise a certain meaning, e.g. engines are optimized for cruise, this is where they are most efficient.

enter image description here

Airbus, cruise parameters page, Source

Aircraft are cruising in a clean configuration, that is all drag sources have been retracted. From Airbus:

enter image description here

Source

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Likely the only aviation terminology difference would be in semantics or context. Such as "the airplane has reached cruise altitude and it is enroute to Miami" (it could also be said that an airplane has reached its planned enroute altitude)

ATC can issue a "Cruise" clearance. Not very often used anymore (the details aren't important for this question) but that would be a specific difference between the use of the terms cruise and enroute.

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