Why Do Airlines Make Small Changes to Flight Times (Ask Cranky)

Ask Cranky, Delta

This is a great question, because I’ve wondered it myself for quite awhile. This gave me the chance to reach out there and see if I could get any more detail. Sure enough, I could. Let’s start with the question.

. . . I booked my tickets last week and got an interesting email from the online travel service this week that my return flights had been changed by the airline. The departure and arrival times were changed by 1-3 minutes, for the most part making the flights a bit longer. For example, my departure from Buffalo was changed from 4:30 to 4:27 (or it might have been the other way around).

Why would Delta make such small changes to the flights? I’m a private pilot and come from a family of pilots, so I’m familiar with airspeed versus ground speed, but there’s no way they can predict the weather nearly two months out; and I know about flying at maximum economical speed as opposed to maximum possible speed, so I’m wondering if the rising fuel prices have caused them to adjust their speeds a bit to save fuel. But that is just a wild guess.

This happens on all airlines, but I’ve certainly noticed it happening more frequently on Delta than others. You think your flights are all set and then you get a schedule change notice saying that the arrival time has moved by a minute or two. Why the heck are they doing this?

I went to Delta for the official response and was told this:

. . . when the schedule is first published, it’s not operationally sequenced, so small adjustments are made on certain routes – basically massaging the departure and arrival times slightly for the best operational efficiency and connectivity. As your reader noted, these are minor, a minute here and there.

In other words, when Delta first puts the schedule out there, it’s not perfectly timed to fit into the entire system. Little tweaks of a minute or two can make a difference. That sounds really nebulous, so let me try to fill in the blanks.

A schedule is put out there nearly a year in advance. Often, that won’t be the final expected schedule. Ask CrankyMajor tweaks happen along the way, but the big ones are usually done when you’re a few months out. There might be some new routes added since the schedule was first put out there. Some routes could be cut, frequencies could change, etc. So at a large airline like Delta, when the schedule firms up, they might find that tweaks of a minute or two on other routes can help.

There are a few other reasons I can think of that would make this worth doing. Look at it through the eyes of the reservation system. This is more of a small change than a big one, but let’s say that Delta flies from Buffalo to Tampa via Atlanta and it takes 4h32m. Then let’s say that US Airways can get you there in 4h30m. If there are a lot of people that fly that route, it might make sense for Delta to find a way to shave 3 minutes off the connection time. That could make it the fastest way to get from Buffalo to Tampa and it could actually have an impact on bookings. Of course, you only do this for larger markets.

There is also the issue of weather. Airlines use historical weather patterns to determine how long flights will take. For example, winds are much stronger in the winter than the summer, so a flight from JFK to LAX is scheduled to take longer in the winter. It’s possible that as weather data comes in, the airlines make slight changes to adjust to the new expectations.

The last reason I can think of for this is simply one of airport issues. Let’s say that Buffalo has construction going on this winter. Delta might want to lengthen the expected flight times to account for the potential ground delays, even if it’s just a few minutes.

I’m sure we have some readers who know more about this than I, so feel free to chime in below.

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26 comments on “Why Do Airlines Make Small Changes to Flight Times (Ask Cranky)

  1. I was wondering if it had anything to do with bettering on time arrival on a chronic poor performing route. Any truth to that?

    1. Probably, yes. If a flight is taking longer than expected, the airline will adjust the times to reflect the actual amount of time it takes to complete the flight. They don’t want to do this for several reasons, many discussed below, but they need to do it to make sure they can stick to schedule.

      BTW, thanks everyone for chiming in on the crew scheduling piece.

  2. I hypothesise that it might do with sequencing at the airport. If a group of flights are all scheduled for 4:30, would moving your flight to 4:28 put you at the front of the line for takeoff slots?

  3. Speaking of schedule differences, what’s with the big jumps in international fights with Delta?

    For instance, I’m flying DL 108 ATL-MAD on 3/25, dep 6:45 and arriving at 8:15. According to Seat Guru, 108 has many different times (as I also noticed in my search for different dates):

    108 ATL 4:40p MAD 7:25a Boeing 767-400
    108 ATL 6:35p MAD 8:15a Boeing 767
    108 ATL 6:35p MAD 9:15a Boeing 767
    108 ATL 6:45p MAD 8:15a Boeing 767
    108 ATL 6:45p MAD 9:15a Boeing 767
    108 ATL 6:55p MAD 9:15a Boeing 767
    108 ATL 6:55p MAD 9:40a Boeing 767-400
    108 ATL 7:05p MAD 9:40a Boeing 767-400

    What gives?! Is it just the plane itself that’s slower? Different winds because of different positioning of the Earth or something?

    Also, why the big jump to 4:40? That starts in April, I’ve noticed. Is that just an equipment scheduling thing? Or did research tell them that travellers want to get there that early in the Spring?

    Just curious!

  4. Also, I have to comment re: Delta and their attempt at making the fleet up to date with Wi Fi etc (previous post from weeks ago)…Can you tell I’m the only one in the office today and already over it?

    Overhead movies on a 9 hr flight to Madrid from your fortress homebase in Atlanta? That’s not exactly up to date! When I flew to AMS on UA in ’05, they even had seatback movies/monitors. That just doesn’t seem right!

    1. Delta is in the process of putting seatback AVOD on all 747, 757, and 767 aircraft that currently do not feature it. They expect to finish in 2013.

  5. I know a thing or two about this stuff, but I’m far from an expert.

    There’s a lot of stuff involved with publishing a flight schedule, from airport operations to crew scheduling.

    Let’s touch on crew scheduling for a moment, as it’s not something that was discussed in Cranky’s answer. Most major airline pilots (and regional ones too, with a notable exception being Southwest) get paid hourly — but only based on flight time. These pilots typically get paid on a “block or better” basis, which means they get paid for the block time (gate to gate) as published in the official schedule, or actual flight time, whichever is greater.

    Yes, airlines “pad” (or whatever term you want to use) their flight schedules. But publishing a block time is tricky — publish one long enough such that no flight is ever late, and you’re paying your pilots for time when they are not actually flying the airplane. This is rather inefficient. However, if you publish a block time that is too short, then you’re still paying your pilots for however long it takes to fly the flight, but you’re also messing up passenger connections/plans because everybody will be late.

    So, some of these itty bitty changes are done to fine-tune timings to support whatever operational goals an airline has.

    Several years ago, I heard a talk from the VP of Operations at Continental. When asked about block times, he said that the “right” schedule was one where 50% of the flights were late, and 50% were early.

    I’ve also been told an airline can “buy” its position in the on-time rankings. That is, if an airline wants to be #1, all it has to do is stretch its block times such that flights are more likely to be on time. However, it incurs a cost (pilot pay based on published schedule) when it does so.

    One thing to add to Cranky’s comments on connection times — make a connection time to small, and the airline can’t sell the flight (every airport/airline has published “minimum connection times” for flights. If a connection time falls below the particular threshold, they’re not supposed to be able to sell the flight.)

  6. A few comments:
    1. Airlines pay pilot pay based on actual block time. Scheduled time is not important except for bidding minimum monthly guarantee. So adjusting is not all that important

    2. The ATL-MAD time changes are due first to the daylight savings time change. It changes first in the US, then in Spain, then they add a flight for summer from JFK and since they only have one gate in MAD they need to stagger the flights to permit boarding.

    3. 2 or 3 min changes do not matter at all. ATC delays, weather, weight, air temp will add anywhere up to 20 min to a flight. They matter for scheduling from a gate availability and then minimum connection times at a hub. It is about creating a ‘legal’ connection time so they are not responsible if you miss a flight.

    4. As for getting a better time by moving a flight up that does not happen. Times to the runway are set by time you call ready for taxi and then route and destination traffic flow. Going from ATL to MLI you generally have no ground stops but change the destination to ORD or LGA and it’s all about traffic flow.

    1. If I may tweak your #1 comment a bit…Block or better, as mentioned above, is a more correct answer. If my actual block time is 20 minutes less than scheduled, I still get paid the scheduled time. If it is 20 minutes more, I get paid scheduled time +20 minutes.

  7. I would also speculate that the tweaks may also have to do with ground operations. Shifting around several flights by minutes may make baggage handlers, etc. more efficient at getting ALL the planes in and out of a terminal.

    1. This part is true, too. I used to work on the ramp for a regional carrier, and the way our flights were set up was that each ground crew was responsible for six flights. It’s fine when there’s so much as a 5-minute stagger between flights, but during one schedule, there were three flights set to go all at exactly the same time. That sorta sucked.

  8. If this happens at a slot controled airport it could be a couple of minute time change to move a flight from one slot time to another to keep a slot or because another flight was added/changed.

    Kind of reminds be when I was 18 (which was eons ago) and working a retail job and we would have to change the price on something and it only changed by a penny. That was back before bar codes so would have to acutally change the price tag on the item. It always seemed like they spend more money to raise the price a penny then they would make selling the item for a penny more….lol

  9. This is the same for all airlines across the board, scheduling is constantly tweaking flights. The gate times, the assigned A/C, the crews, and even the guage of the A/C can be changed multiple times through the life of the flight (i.e. loaded in schedule to safely arrived at destination). These changes occur often in the months before, and sometimes weeks before departure

  10. The VP of Continental was correct in that most carrier publish a block that has an ‘acceptable’ block time and an ‘acceptable’ plane for a given route.

    So, CO may schedule IAH-LAX with block time Xh XXm and on a 738. Closer in, the schedule will get fleeted and tweaked based on an fleet or profitability optimization program. So, a 738 turns to a 753 and a more realistic block time schedule. Then, more tweaks based on airport operational issues such as connection failures, gate slotting, crew scheduling, time of day, the list can go on. It’s true you can fiddle with the ‘on-time’ numbers but still a lot goes into the mix.

  11. It could also have to do with minimum connection times … One minute could make the difference between a valid connection and an invalid connection.

  12. I believe this is all about “on time” departure stats and the legalities of bumping off connections (i.e. no duty for airline to hold/help you out if you miss).

  13. I’ve also seen minor tweaks to block times requested by crew scheduling to make particular pairings legal either at the request of crew scheduling committees (to create a highly productive trip for a crew base that is otherwise not getting a lot of good pairings) or to eliminate an overnight when bumping up against hotel room availability constraints in particular cities where it can be difficult to procure hotel rooms at crew rates (BOS, for example).

  14. Don’t forget to mention the logistics of scheduling crew and aircraft routing. A schedule made a year in advance doesn’t begin to predict how planes and crew will be routed to actually fly them. A few months before departure time the airline will take the thousands of legs that make up a day and find ways to match aircraft and crews to them. Sometimes two flights can’t easily be given to the same aircraft, but only just. Perhaps they would yield only 27 minutes on the ground when the airline prefers 30. The airline will then change one or the other or both flights. Another rationale is to fine tune arrival and departure demand at a hub. If too many flights are scheduled at the same time it makes sense to push some of them around to de-peak. One last reason is that the airline discovers that it has left too little time to connect passengers on certain routes. Perhaps by moving one flight a few minutes earlier or later it can open up several new markets to connect to the outbound flight.

  15. I’ve recently seen two 10 minute changes to the same flight from Melbourne to Singapore on Singapore Airlines. About 6 months ago they changed the flight to 10 minutes earlier, shortly before the actual flight they changed it back to the original time. Sounds still weird to me as on a flight over 8 hours, 10 minutes hardly make a difference.

  16. Don’t know if you wrote about this before, CF, but how about an article why airlines make BIG changes this time? Hehe.

  17. me = continental silver elite = upgrades before merger
    me = gold elite = #19 on list post-merger
    I’ve never been that low on an upgrade list. even as a silver.

    I stand by this: it’s always about money: saving it or forcing more out of passenger.
    I sat next to two platinum elites on my flight from boston to houston today. we were in the exit row. lucky us. whether it’s departure time changes or bilking elites, i’m done with all of this “frequent flier” jazz. the only response from a consumer is “lowest price fare.”

    so say we all (platinum included).

  18. And this cynic chimes in: Another columnist opined that, by changing the schedule times by a minute or so every now and again, flight tracker software like Yapta can no longer match the tracked flights with “real” schedules. How many times have I, as a Yapta user, been met with a message saying my fight can no longer be tracked only to find the departure time is the same but the arrival time is a minute or two different. Not that any airline would be that devious.

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