What is the official FAA definition of the term enroute?

Question

I recently saw a ferry permit which included the following limitation:

Flight in IMC authorized for ENROUTE operations ONLY

Great, IMC is allowed enroute! But wait, where does the "enroute" portion of the flight start and end?

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I did some research and found the following ICAO definition for enroute:

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.

That seems pretty straightforward, but I was looking for something FAA specific and found this in Chapter two of the FAA's Instrument Procedures Handbook:

The en route phase of flight is defined as that segment of flight from the termination point of a departure procedure to the origination point of an arrival procedure.

That doesn't match the ICAO definition, but it also isn't from an actual regulation or LOI either.

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This leaves arrivals and departures as slightly ambiguous, and they often start high in the flight levels where it can be hard to avoid IMC, even on a nice VFR day at the airport (and also seems contrary to what they are trying to accomplish). Are arrivals and departures considered enroute or some other phase of flight?

Answer 1

FAA follows the ICAO definition for describing the phases of flight.

FAA is a member of the CAST/ICAO Common Taxonomy Team that formed the Phase of Flight Definitions and Usage Notes in October 2002. From the CAST/ICAO Common Taxonomy Team site:

Federal Aviation Administration (FAA)- FAA has officially adopted the aircraft make model series (ACFT-MMS) and phase of flight taxonomies as an agency-wide data standard for its internal systems.

So, the enroute phase of flight is the same (just repeating from the same document):

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.

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.

Answer 2

According to the information that @aeroalias found - which I'm sure is correct - the ICAO definition is used "internally" by the FAA:

FAA has officially adopted the [...] phase of flight taxonomies as an agency-wide data standard for its internal systems.

However, as far as I can see, that hasn't resulted in a clear definition in the regulations or the FAA's publications. There's nothing in 14 CFR 1.1 or the PCG and the best I could find - apart from the definition you quoted from the IPH - are sources that imply that en route (or "enroute") refers to cruise flight only and doesn't include departures and approaches. That would conflict with the ICAO definition.

First, section 2 of the IPH says what en route airspace is:

The en route airspace structure of the National Airspace System (NAS) consists of three strata. The first stratum low altitude airways in the United States [...] are called Victor Airways. [...] The second stratum high altitude airways [...] are called Jet Routes. [...] The third stratum allows random operations above flight level (FL) 450.

That's a fairly specific definition that strongly implies that - at least historically, i.e. pre-GPS - en route meant "on the airways".

Second, TERPS doesn't define en route either, but it does repeatedly suggest that approaches and even feeder routes are not en route.

Section 3 on initial approaches says:

In the initial approach, the aircraft has departed the en route phase of flight and is maneuvering to enter an intermediate segment

Section 2 on feeder routes says:

[...] the angle of intersection between the feeder route course and the en route structure must not exceed 120 degrees

That seems to me to mean that a) by maneuvering to start an approach you are no longer operating en route, and b) feeder routes are not considered en route.

Finally, if you look into some of the FAA's legal interpretations, they seem to say that enroute means cruise flight:

Duncan (2014):

[...] pilots serving as SIC during the en route cruise portion of the flight only [...]

Barton (2014):

[...] the pilots identified in both of your questions serve exclusively en route, during the cruise portion of the flight, [...]

I assume that most pilots would agree that descending/maneuvering to start an approach is no longer cruise flight. But unfortunately there's no formal definition of "cruise" that I could find - apart from possibly the ICAO definition - so that isn't entirely clear either.

So my take - and I may be completely wrong - is that even in the absence of a formal definition in the regs, there's quite a lot of FAA material that states or implies that en route means cruise flight on an airway or other defined route, and it doesn't include departures and approaches.

But for a 'real' answer, you might have to ask your local FSDO for their opinion, or even ask the FAA for an interpretation if you need it.

Answer 3

Put simply, en route occurs between terminal procedures.

LAX-JFK

ORCKA1 LAS J146 DVC HBU J10 OBH FOD KG75M DAFLU J70 LVZ LENDY6

Look at the flight plan above, the first and last bit usually indicates the departure terminal procedure (ORCKA1) and the arrival terminal procedure (LENDY6) respectively. Everything in between is en route.

Another perspective is to think of which controllers own that airspace. A flight usually starts and ends in terminal airspace and is managed by the local TRACON. Once leaving TRACON airspace, it is then handed to CENTER controllers along its flight path. Terminal/enroute boundaries vary by location, but you can think of it generally as Class A airspace

Answer 4

Basically, no IFR departures or approaches allowed. Thus reducing the chances of harming the general public during your ferry permitted flight.

After all, a ferry permit implicitly implies there is something amiss with the aircraft, either mechanically or regulatory.