At what point does an aircraft become an airliner?

Question

For me, the term 'airliner' conjures up an image of a passenger jet that is capable of hosting a large number of passengers¹ but I'm finding it difficult to source a reputable definition or etymology despite the term has been sourced int the early 20^th century.

Since the term has been in use since 1908, jet as in jet airliner may be inferred by the modern user but it obviously wasn't part of the original definition.

The word itself would seem to indicate that airliner refers to an aircraft used by an airline (a company that provides air travel for the public), but would that extend to bush pilots with small prop-driven Cessnas or passenger helicopters?

airliner - A large passenger aircraft. A large plane for carrying passengers: a commercial/commuter airliner
  _{source: Cambridge English Dictionary}

airliner - An airplane operated by an airline
  _{source: Merriam-Webster Dictionary}

  _{Is this an 'airliner'? How many passenger seats need to be added before it becomes one?
  (image courtesy of The Bush Pilot Company)}

The term seems so vague that even the airliner tag on this site only uses 'large' to define size or capacity.

Some reference work definitions include cargo aircraft but the predominant emphasis seems to be on passenger aircraft with no upper or lower limit criteria.

I suppose that this term could be relative to the observer or situation but if the term 'airliner' was used in FAA regulations then I'm sure there must be an appendix somewhere that provides a definition. My research has come up empty.

Apologies if this is a dumb question and the term is intentionally meant be vague with only 'large aircraft' or 'many passenger' as criteria. Given proper references as support, that could be an answer.

---

¹ _{This previous question got me wondering exactly what was the criteria before any aircraft could be called an 'airliner'.}

Answer 1

I think there's a misunderstanding here that airliner ("an airplane operated by an airline") is directly derived from airline. While it is a reasonable definition, "airliner" predates airline. (Mirriam Webster: airliner 1908, airline 1910).

An airliner is a portmanteau of air and liner, a liner being any passenger ship plying between ports along regular "lines" (as distinguished from transient ships using those ports). By the early 20th century a liner was generally understood to mean any large, passenger-carrying vessel operating a route between major ports (think Titanic etc.). You'll notice how airliners travel between airports - nautical words and phrases were adopted in the early days of flight.

So an airliner should be

• passenger carrying
• large
• travels between airports, rather than having one fixed point of operation

It's a definition that still fits, and covers any commercial aircraft over a certain size. While there's not a specific point at which an aircraft becomes large enough to be called an airliner, I think it does impart some sense of largeness or capacity that an 'ordinary' plane does not possess.

(You might even say that a better definition of airline is "an air transportation system that operates airliners"!)

Answer 2

The term airliner generally does not refer to a particular aircraft, but rather a whole aircraft type. This makes the literal definition of the word by Merriam-Webster

An airplane operated by an airline

somewhat invalid since this can only apply to a single aircraft.

The key difference between an airliner type and other types is that the aircraft manufacturer works together with airlines during the design process, meaning an airliner is designed to be operated by airlines. Airlines will define what they expect of a new airliner in terms of passenger capacity, range and fuel efficiency. The manufacturer can then design a new aircraft based on these design constraints. This ensures that the airlines get the aircraft they want and that the manufacturer can sell the new aircraft.

E.g., Boeing launched a new version of the 737 MAX after Ryanair requested an increase in passenger capacity, the 737 MAX 200:

Boeing developed the 737 MAX 200 in response to the needs of the fast growing low-cost sector, which is forecasted to account for 35 percent of single-aisle airline capacity by 2033. While the heart of the single-aisle market will remain at 160 seats, the 737 MAX 200 will provide carriers like Ryanair with up to 11 more seats of potential revenue and up to 5 percent lower operating costs than the 737 MAX 8, driving economic growth and increasing access to air travel.

^(boeing.com)

This does not mean every Boeing 737 will be operated by an airline. Boeing even produces a dedicated version for the private market, the Boeing Business Jet (BBJ). But the type was designed with airlines in mind. This is what makes the difference compared to a non-airliner, which is designed with other customers in mind (private or commercial, but not airlines). Again, some aircraft of this non-airliner type might be used by an airline and hence be technically called an airliner according to Merriam-Webster, but the whole type is not an airliner.

Answer 3

The term “airliner” is absent from the FAR/AIM. Maybe a definition can be inferred to mean any aircraft not in the Normal Category. And/or one that is in the Commuter or Transport category.

23.2005 Certification of normal category airplanes. (a) Certification in the normal category applies to airplanes with a passenger-seating configuration of 19 or less and a maximum certificated takeoff weight of 19,000 pounds or less.

This is an inexact way of loosely defining airliner. It would kind of make sense since the pilots generally flying them are Airline Transport Pilots. The only reason I mentioned the ATP certificate is that there are few if any references that combine Airline with any quantitative way of measuring aircraft size. Technically, a type rated private pilot can fly a B747. Or, at least I see no restrictions against it in 61 nor 91.

Part 125 also addresses aircraft over 20 seats and 6000 pounds of cargo capacity. But, I wanted to be inclusive of everything above 19000 lbs and 19 seats. Regardless, neither part completely and adequately addresses the original question since the term airliner is never used. Only interpretations from the Merriam-Webster dictionary seem to offer any insight.

Answer 4

In reality, the word is used in (at least) two different manners, which inevitably leads to some confusion.

On the one hand, an airliner is ANY aircraft, however small, that is operated by an airline company, in contrast to those owned/operated by a private pilot.

The second, probably commoner definition is size-based, though somewhat loosely. In the 1930's, a luxury airliner may have had less than a dozen seats, while these days nothing short of about a hundred seats would normally be regarded as an airliner.

Answer 5

The word pretty much means what it's more or less consistently used for - there certainly isn't any formal definition to get hold of.

The characteristics of an airline though would be to own a fleet of vessels, that ply particular routes, that generally travel distances further than a typical privately-owned craft might be expected to cover, according to some sort of schedule, as a service.

An airliner would be the kind of craft that could be expected to live its working life in that kind of service.

And that's about as good as you'll get.

Answer 6

An airliner is any commercial aircraft that regularly flies the same route, or "line," regardless of the size or capacity of the aircraft. Airliners are operated by airlines and while the big jets are what typically come to mind, airlines also operate smaller prop planes on shorter lines and these are still airliners.

It's the service the aircraft performs and not the type of aircraft that makes the difference. E.g., a 747 owned by the Sultan of Brunei is not an airliner. But if an airline bought it from him it would then become an airliner. If the airline later sold it back to him it would then cease to be an airliner. Another example are the 747s (technically VC-25s) that are typically used as Air Force One.

Answer 7

For many vague terms without specific, precise legal or regulatory definition, the answer will rarely be binary, True or False. It helps to think in terms of probability. If you ask the question: "Is this an airliner?" to 100 random people, how many would answer yes?