Why Do Airlines Switch Airplanes on Flights with One Flight Number? (Ask Cranky)

Ask Cranky

It’s time for another installment of Ask Cranky. This question is a great one, and I could have sworn I wrote about it before. But my intensive (read: 10 second) search didn’t turn up anything. Even if I have, it’s worth addressing again.

I often take UA 732 from SEA to ORD, “with continuing service to Jacksonville”. Every week, at landing they announce “there will be a plane change for passengers continuing to JAX…” If the plane isn’t the same, how exactly is this a “continuing flight”? Why doesn’t the ORD to JAX flight just have a new number?


You guys have probably seen this a million times, because it’s a very common occurrence. In this case, United flight 732 looks like this:
Lv Seattle 6a Arr Chicago 12p
Lv Chicago 126p Arr Jacksonville 451p

You would think that with one flight number, it should be the same airplane the whole way through, right? That’s not the case. In fact, this flight is scheduled with two completely different aircraft types operating each leg. The first is on a 757 and the second on an A319. What gives?

Back in the early days, one flight number would usually have one airplane the whole way. Heck, it was more likely for the airplane to stay the same than the actual airline! (There used to be interchange flights where one airline would take theAsk Cranky airplane part of the way and then they’d turn the airplane over to another airline to go the rest of the way.)

But in the 1980s and 1990s, the airlines started getting (too) smart (for their own good). They realized that in the Global Distribution Systems, nonstop and direct flights (the latter being flights with a stop but no change) received preference. And just like with Google search results today, those flights that showed up first got the most bookings. The airlines wanted more of that so they started designing flight numbers to match those routes with the most demand.

It got out of control quickly as airlines tried to cheat the system. I remember flipping through a timetable when I was young seeing Delta with a ton of high four digit flight numbers that were all assigned to the same flight. So maybe you would see London to Atlanta as one flight, but then they would overlay a bunch of flight numbers so it looked like you could go on a direct flight from London to all the big cities in the US. I don’t remember when that stopped happening, but I assumed it was a government regulation that ended that misleading practice.

But that didn’t mean airlines still couldn’t get creative about how they assigned their flight numbers. It didn’t take long to realize, however, that the flights that were ideal for marketing as direct weren’t the same flights as what would be ideal from an operational perspective. Certain aircraft had to go to maintenance, others just weren’t the right size to operate both legs. So the operational side of the airline started shifting airplanes around regardless of the number attached. That’s where we are today, at least with most airlines.

You still see the old method when you fly Southwest, but that’s the extent of it with large airlines. I don’t know numbers, but I’d imagine it’s less common for one airplane to work multiple legs on a flight than it is or there to be a change in the middle. And that’s because the marketing and operational arms work in different ways. There is now actually a third consideration as well.

Airlines are running out of flight numbers.

With all the codesharing occurring between airline after airline, the big guys are running out of four digit flight numbers. Could they go to five digits? Yeah, right. It would take the industry years to do the programming work required for something like that. Instead, the airlines start cramming more flights on each flight number.

Delta flight 4509 goes from LAX to San Diego and then back to LAX. Clearly nobody is taking both segments of that flight, so why bother lumping them together? Because there just aren’t enough flight numbers to split them apart.

And that’s why you see some goofy things with flight numbers today.

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51 comments on “Why Do Airlines Switch Airplanes on Flights with One Flight Number? (Ask Cranky)

  1. Delta has a one stopper from SLC to KOA that doesn’t even appear as having the stop at LAX if you don’t look carefully!

  2. United 872 and 483 have no less than 3 segments each. The city pair? DCA-SFO… How far down in GDS? No.s 6 and 10.

  3. I just think it’s crap that you only get mileage for the beginning/end cities in a direct flight, and not the stop. Two US Airways examples: US449 EWR-CLT-SLC would be 2256 miles if the flight number were different, but you only get 1969 because it’s a “direct” flight. And US700 LAX-PHL-FRA: 6350 actual vs. the 5806 you get from the “direct” flight.

    1. TBH, that’s the biggest sin in my book. I kinda sorta get a one-stop with no change of gauge, WN style. But if I’ve got to change planes, that’s a connection. I can live with a connection, ’cause I’d have to on any other flight But then they have the nerve to give me less frequent flyer miles? Unless the ticket was cheaper, that’s just wrong.

  4. Delta still does this regularly. For the longest time DL11 was MCO-ATL with continuing service to LGW, and I know they weren’t taking that crappy 757 all the way to London.

    I got burned by this once on what I thought was an LAX-MCO non-stop. First I couldn’t find the gate because my boarding pass printed as LAX-MCO and the gate was marked for LAX-MEM. Then, once I got to MEM, they refused to put me on the medallion upgrade list since I was on a “direct” flight and they ended up flying the FC cabin on the MEM-MCO leg mostly empty with this Platinum in coach (their policy on direct flights is that you upgrade the entire way or not at all). And to add to the indignity, they only gave me mileage (and one segment) for LAX-MCO direct, not including the significant extra distance flown by connecting through MEM.

  5. My experience with American airlines is that they (unlike United) actually use the same plane if it’s the same flight number.

    1. Not so. Yesterday, I checked in at JFK for AA 1458 from New York to PDX (Portland). The agent at the ticket counter saw that 1458 went from JFK to Phoenix then 1458 from Phoenix to PDX. He told me that it was the same plane. “So I don’t get off the plane in Phoenix?”, I asked him. “That’s right, stay in your seat” , he replied. When AA 1458 reached Phoenix, I stayed seated until the plane was empty. Only then did a flight attendant tell me that the plane was not going to PDX. I had to race to a gate on the other side of the airport to catch AA 1458 from Phoenix to PDX. The gate was closing, but they let me on. None of the staff were willing to apologize for the mishap. I felt like I had been mugged by AA.

  6. I’ve never liked ‘change of gauge’ flights, they were connecting flight no matter what anyone said.

    Years ago when I worked at TWA, I thought they were the king of ‘COG’, but they didn’t do anything PanAm wasn’t doing either. Back then it would be the phantom flight number say 777 CMH-LHR, but it would really be flight 146 CMH-JFK and flight 700 JFK-LHR so in CMH they would be calling the boarding of flight 146 and 777 for the same aircraft. A bigger city like LAX or SFO could have four flight numbers on that one flight to JFK since the phantom numbers would be used beyond JFK to other cities in Europe.

    People would be surprised when they checked in for the first flight and were given two boarding passes for their trip. That was usually the first time they found out they had to change planes somewhere.

  7. “They realized that in the Global Distribution Systems…” — I thought it was a regulatory issue some time in the mid-80s, possibly prompted by a lawsuit, that caused this change in GDS behavior. I read about it in a book once so I’m not sure about the details, but I think it was at attempt to stop manipulation of search result where an airline would pay a GDS to move its flights higher up. The ruling was, I believe, that direct (same-airplane) flights had to show up first (no provision for non-stop), followed by same-airline connections, followed by everything else. Among other things, this ruling gave rise to a much tighter coupling between regionals and mainline airlines, because a regional flight that didn’t show up as the “same airline” as its mainline connection would go to the bottom of the list. This regulatory decision contributed to the development of the hub-and-spoke system in the first decade after deregulation. Again, I’m not clear on the exact details.

    At any rate, I think the practice of marketing change-of-gauge flights as “direct” is deceptive. I don’t care much about the flight number, but there are clear advantages to staying on the same plane — the airline is less likely to lose your bags, and you’re substantially less likely to misconnect. So the marketing advantage of a “direct” flight should go with the plane, not the flight number. It’s also time to change the terminology, since in everyday language, “direct” is often used to mean non-stop (even among Southwest fliers). Using “direct” for same-plane, multi-stop flights is a relic of the days when cross-country flights always (or at least typically) involved stops; today it’s just confusing.

    1. Ron your comment reminded me of a funny story from eons ago when I worked for TWA. A woman called up who must have been coached on what to ask for. She said “I want your direct flight from Los Angeles to JFK”. I figured she meant nonstop but had to respond correctly so I said “We don’t have direct flights to JFK. We have four nonstops to JFK, a direct to LaGuardia, and connecting flights throught out the say to all three New York area airports JFK, LaGuardia, and Newark. Could I offer you one of our nonstop flights to JFK?”.

      There was dead silence on her part, then she said “Yes nonstop would be fine. What’s the difference between nonstop and direct?”.

      So I explained the difference to her and I have a feeling after she got off the phone, whomever coached her to ask for ‘direct’ must have gotten a hear full…lol

  8. My biggest complaint is that you book one flight number and you expect not to have to worry about making a connection. I once booked American Airlines from Montego Bay in Jamaica to JFK as a single flight with a “Stop” in Miami. When my plane was delayed in Montego Bay – I reasoned “No worries” in Miami as they will hold the flight from Miami to JFK since they would “never” have two planes in the air with the same flight number at the same time, right? Wrong. Got to Miami, no flight. So AA had two flights in the air with the same flight number at the same time. Makes perfect sense to me……

    1. Wow, operationally that scares me. Especially depending on the timing it seems that there might be a large potential for confusion with ground controllers if two flights are in the air with the same flight number…

      1. From an ATC perspective, they are seen as two different flight numbers. They use different designators if they’re both in the air at the same time.

        1. Exactly. Thanks to Channel 9, I’ve been on United flights where the callsign flight number was totally different than the airline flight number, and other times where they’d appended a letter (e.g. United 900C for the SAN-SFO leg of UA900 SAN-SFO-LHR).

          One time while I was out taking pictures at SAN with my scanner, there was a flight to LAX where the controller was having trouble getting the flight plan filed. Figured out because there was another flight in the system with the same number currently in the air, and sure enough it shows up a few minutes later landing from LAX — in that case, the two legs of the LAX-SAN-LAX trip were on different aircraft, and thanks to delays (probably flow control at LAX) could have been in the air at the same time.

    2. That makes sense. The flight was late out of Jamaica so they must have used an extra plane to still operate the MIA-JFK portion, that happens all the time.

      That or it was a change of guage flight two separate flights numbers for each leg and through phantom flight number for the MBJ-JFK listing in the GDS.

  9. One advantage to the customer is that these “direct” flights don’t count as a stopover for the purposes of the fare rules.

    For example, many of United’s transcon fares say something to the effect of “2 transfers permitted on the pricing unit.” But if you take a direct flight, the stop doesn’t count as a transfer, so you can effectively get an extra transfer point for free.

    That’s not often going to be useful, granted, but it’s something.

    1. As a corollary to this point, I believe that a passenger booking a “direct” flight is exempt from Passenger Facility Charges and September 11th Security Fees for the intermediate airport, even if a change of planes is required. This definitely used to be the case — it might still be.

  10. UA recently had a flight 1737 that went PDX-EWR-LAS, while it’t’s companion flew JAX-EWR-PDX.”

    NW was notorious for plane changes in MSP with the same flight number. It was easy to note them since the layover was nearly 2-hours rather than the tipical 1-hour.

  11. I dont think this practice should be legal….As much as I hate all of the airline regulations that have come out lately, and I believe about half are not actually customer friendly, this is deceptive, even to us so-called experts.

    IF there is a plane change, there SHOULD be a change of flight number (operational constraints can get an exception).

  12. I wonder if the count as multiple segments for FF consideration – I have never gone the segment route to status so I don’t look at them.

    1. No they do not. I experienced this last year. MIA to ATL to SDF. Same flight number but a change of planes. Only got credit for one segment. I com

  13. I’ve complained about “change-of-guage” flight numbering practices for years, to DOT, at least so there is a record of someone making an official complaint, and directly to UA, my primary carrier, which doesn’t need to wait for DOT to tell them to stop it.

    I argued to UA, after they had delayed a bag, that “change-of-guage” in all probability had a major part in causing the delay. I wrote that this practice is (1) confusing, (2) frustrating, (3) deceptive, and (4) inadequately described in flight listings.

    To put it bluntly, this practice is dishonest. These flights are connecting flights, and as such, should not be marketed as direct flights

    UA responded to my complaint with the argument of “limited quantities of flight numbers.” Granted, there are limited numbers, only 9,999 numbers that fit the 4-position record of the rez system. But, does anyone come close to operating that many flights a day?

    Well, UA gave me some FF “goodwill miles, but didn’t indicate there would be any changes. In fairness to UA, their new web site rez system display of flights does more clearly disclose pertinent information about the change-of-guage flight. That, however, does not cure the confusion and frustration this type of operation brings to the traveller.

    I will always consider this practice, purely and simply, dishonest. These are connecting flights and to continue to list and/or call them anything other than connecting flights is an insult to me and to my English language.

  14. I could care less about LAX->SAN->LAX since no one would book that, and it saves flight numbers. Although, I’m curious for ontime reporting does each leg count as a flight or does just the whole flight number?

    Re: Expanding to five digit flight numbers.. I’ve often wondered if airlines could/would just pick up another IATA code to stash their codeshares under… Although that seems like it could be too much of a kluge and cause problems elsewhere in the system..

    1. I’ve done flights like that, once did IAD-PHL-IAD, all as the same flight number, doing LAX-PHX-LAX as the same flight number twice later this year. It is nice because in all my looking, they use the same equipment, so even if the inbound is late, you won’t miss the outbound.

  15. CF – Isn’t it also true that on direct flights with equipment change; should the first leg of the flight be delayed they hold the second from taking off until those passengers make the plane change/connection?

    1. No, that’s not true. If the first flight is late and the second airplane is ready to go, they will make a decision to hold the flight just like they would for any connection.

      1. When I book a connecting flight, my parents often ask me if it’s a “guaranteed” connection. I’ve never heard the term except from them, so I’m guessing it’s something that ceased to exist when I was a kid.

        I certainly remember one time when we missed a connection that my parents thought was guaranteed — our TWA flight Paris–JFK was about 4 hours late, by which time our supposedly guaranteed connection JFK–Boston was long gone. We ended up in a taxi to La Guardia to catch the Eastern Shuttle. This was in the summer of 1981, only a few days before the big walkout.

        Anyway, was there ever such a thing as a guaranteed connection? What did the guarantee mean?

        1. Same year, ’81, BCal’s IAH/GAT/EDI service promised a guaranteed connection for the GAT/EDI leg. Late into Gatwick, BCAL put us on the helo (and paid the freight) to LHR to catch the BA shuttle to EDI, a grimy Viscount.

  16. I remember those “scheduled aircraft change” flights in the back of the Delta timetable. Weren’t they 6000-series flight numbers? I’d stumble across them in the listings too, but never seemed to notice them in real life. Now I know why.

    1. And then there was “through flight” TW 731 MUC-FRA-JFK-PHX-TUS. A 72S to FRA, then a 747 to JFK, an L10 to PHX, and another 72S to TUS. IIRC, the real flight from FRA-JFK was 701, but it also “carried” flight numbers 711/721/731/741. There were occasions where the PHX-TUS leg departed before the L10 got in from JFK. Couldn’t hold it, or they’d take a crew rest
      delay the next day. I think TW in PHX sent their misconnected TUS pax to HP.

  17. I didn’t look today to see if it still applies, but CO had an AUS/IAH/LHR with the same flight number, with a change of a/c in IAH last fall.

  18. DL 5 (and before that DL 1) was MCO-LHR. there was a plane change at JFK. i took the MCO-JFK portion of it weekly on a junky old 738 (definitely not TATL metal).

    this recently changed. now the MCO-JFK has its own flight number DL1221.

  19. Why not keep the 4 character limit and add in letter into the 4th spot. That would add thousands of additional flight numbers, and regulatory-wise, letters could denote codeshare or something…

  20. What about the longest by distance?

    QF 107/108 would be a good chance (SYD-LAX-JFK and vv).

    Or multiple flights Europe-Australia / UK-Australia with same flight numbers but stops in SIN/BKK/HKG.

  21. Here’s the deal, at least how I understand it:

    “Non- stop” = no stops
    “direct” = stop(s), but same aircraft
    “connecting” = stop(s), change of aircraft

    1. In practice, it’s:

      “direct” = stop(s), but same flight number
      “connecting” = stop(s), change of flight number

      1. Since several legacies have flights with the same number (DL, CO in evidence above), what then would you call a flight with a stop, change of a/c, and the same number?

        1. I would call it a missed connection waiting to happen. Yesterday I checked in at JFK for AA 1458 to PDX (Portland). The agent at the check- in counter saw that AA 1458 went from JFK to Phoenix then AA 1458 went from Phoenix to PDX. “So I stay on the plane in Phoenix?”, I expressly asked him. “Correct”, he answered. When the plane reached Phoenix 45 minutes late, I courteously stayed seated as the other passengers raced for their connections. Only when the plane was completely empty did a flight attendant tell me that the plane was not going to Portland. I had to race to a gate completely on the other side of the airport to get on to AA 1458 to PDX. The gate was closing but I got on at the last minute. None of the AA staff were willing to apologize for the misinformation I was given and the fit of exercise-induced coughing that I experienced.

  22. Sometimes it may be for the market it serves… Before Emirates came into the scene, Delta had flight 8 From IAH to ATL on an MD then continuing to DXB on a 777. I’m sure it had plenty of Big Energy clients with little to no alternatives.

  23. Back in the 90’s WN had a direct flight between Los Angeles and Detroit, but you may not have wanted to take if over a 1-stop and connection like a lot of Southwest flights operate. Why, because the direct flight made 7-stops between LAX and DTW. A slow time at TWA so a coworker and I tried to find the WN flight with the most stops and that flight seemed to be it. You could book it at the same price as a shorter 1-stop/connection flight.

  24. It’s very deceptive marketing. I suggest mandating that if an airline misconnects a flight that it disingenously markets as ‘direct’ there should be a mandatory, substantial fine paid to the customer.

    1. When you go to search for tickets, at least on united, it is made very clear that there is a stop at an airport, how long the stop will be, and that there will be an equipment change (where applicable). Hardly deceptive if you ask me, or probably any lawyer.

      1. Not true. Yesterday I flew AA 1458 from JFK to Portland. My ticket said only that the equipment was a 737 and there was 1 stop in Phoenix. “Do I stay on the plane in Phoenix?”, I expressly asked the agent at the JFK check-in counter. “Yes, the same plane will take you to Portland”, he told me. When AA 1458 reached Phoenix 45 mintues late, I courteously waited in my seat while other passengers raced for their connections. Only when the plane was the only passenger remaining on the plane did a flight attendant tell me that the plane was not going to Portland. I had to run to a gate on the opposite side of the airport to catch AA 1458 from Phoenix to Portland. The gate was closiing, bu they let me on. None of the AA staff were willing to apologize for the misinformation or the fit of exercise-induced coughing that I was experiencing. Deceptive? Yes. Liable? The courts can decide.

  25. another reason for the same flight/change of guage: the flight can be treated as a “through” instead of a connection for purposes of connecting time (which is typically longer) at the airport. the result is that the total elapsed travel time from point A to C (via B) is shorter on the “through” flight and it therefore shows up earlier on GDS displays for sale.

  26. docjames, I’d reckon Air NZ’s LHR-HKG-AKL onestop would come high in the distance rankings: BA is down to one routing for LHR-SYD now, via SIN, and Qantas has LHR-SIN-SYD and LHR-SIN-MEL only: Virgin Atlantic is now the only LON-HKG-SYD flight. Last time I looked, Air Austral – yes, the one that is buying 800-plus seater A380s – had a CDG-RUN (Reunion Island)-SYD-NOU (Noumea, New Caledonia) run twice a week, that probably holds some sort of distance record.

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