Train and bus lines usually have a number of stops along the way where some passengers can get on and off, while the rest stay onboard and continue to their destinatiom. For sufficiently long routes, drivers may be swapped out in the middle of the line, and the bus can be refueled, while passengers stay inside and continue their journey after the stop. But on all the (non-direct) flights I have taken, everyone must get off on the first stop, and get onto a different plane with a different crew to get to their final destination. Why? Are there any commercial flights with at least one stop in the middle, where some but not all passengers get on and off, while everyone else stays on the plane? If yes, why are they so unusual? If no, why do they not exist?
These "direct" flights are actually not unusual, at least in the US. I was surprised by this discovery based on the routes I personally tend to fly, but fortunately we have the Bureau of Transportation Statistics to provide objective information. Using the July 2019 data for all major carriers, I identified direct flights by counting multiples of the same flight number on the same day with the same aircraft, as opposed to single-segment "nonstop" flights. Here's what I found:
Some interesting notes:
- Over a third of all flights are direct.
- The practice is not limited to low-cost carriers. In fact, the two largest traditional carriers (American and Delta) operate around half of their flights direct and together operate almost two-thirds of all direct flights.
- Nevertheless, Southwest uses more direct flights for its size than any other airline, nearly rounding out the other third.
- On the other hand, JetBlue, which is commonly considered a low-cost carrier, barely operates any direct flights. Other low-cost carriers use anything from zero (Allegiant) to about a quarter (Spirit, Frontier) direct flights.
- The other traditional carriers use direct flights sparingly. Hawaiian flies only nonstop routes, which makes sense.
I may have missed a few direct segments that departed past 12am on the day after the previous segment, but I don't think there's enough of those to substantially alter the results. In any case it would just increase the number of direct legs.
It'd be interesting to run some more analyses to see historical/annual trends in the practice, but that would require someone with more patience and/or computing power than I have. These data sets are huge and can only be downloaded month by month. I chose July 2019 because that was about the peak of commercial passenger aviation.
There's also some fun aviation memorabilia associated with these "direct" flights: (source)
On airlines with no assigned seats, plastic cards like this used to be provided so that even the passengers continuing on could deplane if time permitted. Somewhere I have a couple old ones from Alaska Airlines. Nowadays I believe the airsickness bag doubles for this purpose in some cases. I suppose if you really didn't want someone to take your seat, you could leave a full one behind.
Note: A previous version of this answer had a much lower count of direct flights. Turns out Excel just wasn't done calculating yet.
These are known as “direct” flights. They aren’t popular because each stop adds an hour or more to the travel time for through passengers, so they are significantly slower than non-stop flights yet little better than a connection.
This actually used to be the norm, but in the last few decades most larger airlines have moved to a “hub and spoke” model with plenty of connections at the hubs. They may have some spoke-hub-spoke or hub-spoke-hub direct flights on the books, but in practice virtually all of the passengers change at the midpoint. It is quite rare to see hub-spoke-spoke or hub-hub-spoke direct flights.
Some hub-less low-cost carriers still feature direct flights.
As others have pointed out, “direct“ flights do exist. The airline will have the same plane travel from one city to another with a stop or two along the way. On those flights some passengers will disembark at the stop as that is their destination. Other passengers will get on at the stop to go on to the other destination.
Flying out of Love Field, this arrangement was the norm with Southwest Airlines. This was due in part to the Wright Amendment. Since, I now mostly fly American Airlines out of Dallas Fort Worth Airport, I do not know for certain how much the repeal of the Wright Amendment has changed this. But, I do know that it is still relatively common.
The longest flight that I personally know of that did this used to be South Africa (probably Jo-burg) to Texas (Dallas or Houston) via Morocco. To my knowledge, this route no longer exists.
why are they so unusual?
You could turn the question around and ask why bus and train companies run sectors where the vehicle is mostly empty and making a loss. Often it's because the city requires a minimum level of service for remote areas as part of the franchise.
Also, it's cheap and easy for a bus or train to stop and change passengers, but an airline might find it more efficient to use a smaller plane for the 'spoke' flights and a big one for the hub-to-hub flights.
That's just because of your city-pairs.
What you're really saying is "Everytime I fly, I must go to an intermediate "hub" airport and change planes". That's not true for everyone, it's just (all due respect) true for you, because of the airlines and city-pairs that you do fly.
It's actually perfectly common for an airline to have a "numbered flight" that flies from city A to city D to city M to city Q to city W. It's the same aircraft, with the same flight number, and sometimes is serviced or changes crews enroute, rather like a train or bus actually.
The crew changes aren't necessarily due to exhaustion; often they're to return the crew to "home base" at the end of the day, so they can go back to their families, without the airline having to pay for hotel, transport, per diem etc.
For instance, pre-COVID, a US airline (Southwest) flew a whole bunch of cities. And they tended to scramble up which flights flew which routes, so that most city pairs had a straight-through flight if you waited long enough. Let's take a hypothetical airline, and wanted to get from city A to R... here is a day worth of eastbound flights, each typically 3-4 hops:
114: A - E - N - Q - X 121: A - G - M - T - Y 128: B - E - R - W 131: B - F - M - S - X 133: C - G - M - R - Z 189: A - H - L - R - W
So for instance, I could fly Flight 114 then change planes at E to flight 128. So that's exactly like your experience; you have to change planes somewhere.
Or I could fly Flight 131 and change at M to Flight 133. In this case, I'd go through F, but I'd stay on the plane. So no gathering bags and piling off the plane etc. I'd still have to change planes at M. That's where Spirit differed from Southwest; Spirit would kick you off at F, even though you'd get right back on the same plane. All of them may do that today due to COVID cleaning.
Or if I waited until later in the day, I could fly flight 189 and not have to change seats, though we would still stop 2 places.
Notice how none of the flights from A and B go to the same destinations twice. That's an example of the airline "scrambling it up" so most city-pairs have at least one flight a day with no plane changes, specifically to serve customers like you who dislike them enough to settle for that flight time.
Southwest Airlines in the US does it all the time. Here's a flight from Houston, TX to New York, NY that has a stop in Atlanta, but still only a 5 hr flight end to end.
Note the "1 STOP - no plane change" here on the flight listing on their website:
And checking on the actual flight tracking shows the stop in Atlanta, but both legs are the same flight number. From my experience, ~1/2 the passengers will stay on the plane.
Widerøe definitely do this in the north of Norway. You can read about one traveller's experience of the Tromsø-Hasvik-Hammerfest-Honningsvåg-Mehamn-Vadsø-Kirkenes "milk run" here:
Here in Finland, I know that (pre-Covid, anyway) one of the Helsinki-Kemi flights had a short stop in Kokkola.
There are various intercontinental, some as extra stop, and some as "triangle flights".
E.g. Air Canada going from Canada, to Argentina and then Chile and then to Canada (or the contrary). If you need to go to Chile, you have a stop in Argentina, where there is change of people. But if you stopped in Argentina, at flight back, you will stop in Chile.
There is also KLM (really "KLM Asia"), from Amsterdam to Taipei and then to Manila. And then back: Manila, Taipei, Amsterdam. So you have a stop to get new passengers (and fuel).
In US some years ago I booked a direct flight from Seattle to Boston, and I was very surprised that such flight stopped in Denver (and just few passengers stay in, for the full journey). [By the way, it had also an unexpected technical stop in Hartford, because of lack of sufficient fuel, because of unexpected traffic at destination]
This is basically a milk run flight. I'm aware of two: Alaska Airlines runs one in Southeast Alaska from Seattle to Anchorage, and United runs one in the Pacific, from Honolulu to Guam. I've been on the Southeast Alaska one—if you're a through passenger, you don't really have time to get off the plane and use the airport facilities.
Most of the answers focus on the US, but there are lots of such flights on international routes, at the very least on the Europe-Australia flights operated by European or Australian airlines, most of which have a stop somewhere in South-East Asia (Singapore, Bangkok...).
Those flights are long enough that all passengers actually deplane before re-boarding (and they do a quick clean-up in the meantime), but IIRC you can leave your stuff on board. Of course, all crew will change at the intermediate stop.
This is becoming less common as many airlines have a tendency to do partnerships with one airline flying each leg with its own aircraft.
If you go back a few decades (before long-haul aircraft), it was very very common. The same "flight" (using the same number and aircraft) was actually a succession of many shorter hops up to the maximum range of the aircraft. The Kangaroo route used to take well over a dozen stops.
This also used to be called "continuing service". Like "flight 123 to ABC with continuing service to XYZ". But then the airlines started getting creative and using the same flight number but not the same plane or crew so they could market it as one flight and show up higher in search results.
One other reason why this is less common (besides spoke-and-hub in general) is that airlines have gotten much more deliberate about filling every seat. So in the above link, the first leg uses a slightly larger plane than the second leg. Probably the smaller plane is too small for the first leg, but the second leg doesn't have enough traffic to justify a larger plane.
I have seen this when there were two airports really close to each other (flight A to B to C where B to C is very short). My guess was that people from A were willing to pay enough extra to get to the exact airport that they wanted that it was worthwhile, but no one would actually pay to go from B to C if they weren't already on the plane so it wasn't worth keeping a second plane there. Or maybe some VIP lived there and really wanted it--crazier things have happened.