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

Thanks,
Patrick

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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