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I've noticed that many times 2 or sometimes more airlines will have aircraft departing the same airport within minutes of each other heading for the same destination. For example at this moment UAL 98 and QF 94 departed LAX at roughly the same time heading for Melbourne Australia. As I type they are flying almost in formation over New Caledonia. I see this again and again from regional flights to trans ocean flights. I can't imagine that both flights are full every time. What is the rationale for competing airlines to fly at the same time and arrive at the same time?

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    On some routes, there's only a short range of time when aircraft can leave one airport when it's open and arrive at the destination airport when it's open too. Could it be that?
    – Gagravarr
    Nov 2, 2015 at 18:41
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    Not code share...one was an Airbus the other was a Boeing.....
    – doug r
    Nov 2, 2015 at 19:17
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    @Prashant Code-shares tend to leave at exactly the same time.
    – David Richerby
    Nov 2, 2015 at 21:37
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    It's the same reason that there are lots of buses at 5.30 pm and not so many at 3 am. It's when people want to travel.
    – Calchas
    Nov 3, 2015 at 0:50
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    @DavidRicherby I'd hope that all code shares leave at exactly the same time. If not, I'd like to be on the part with the wings, tail, fuel, and pilot, please.
    – Jon Story
    Nov 4, 2015 at 10:21

9 Answers 9

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In addition to the practical considerations noted in the other answers, there's also the fact that the internal logic of competition (Hotelling's Law, as helpfully pointed out by AE) is an incentive for each airline to schedule their flight at the same time as the competing flight.

Suppose there are a certain number of people who need to go from PPP to QQQ. Each traveler has an ideal time they would like to fly, and will buy a ticket from the airline that comes closest to that.

Now if airline A has a departure at 10:00 and airline B has a departure at 12:00, airline A can improve its market share by moving its departure to 11:00 -- namely, the passengers with a preferred departure time between 11:00 and 11:30 will then switch from B to A, and everyone else stays with the same airline. Those who prefer to go before 11:00 flew with A before and still do; those who prefer to go after 11:30 flew with B before and still do.

After some maneuvering of this kind, airlines A and B will end up having both their departures scheduled right next to each other around the median of the customers' preferences, sharing the market about equally. In this situation neither airline will have anything to gain by moving their departure -- on the contrary, that would leave them as the best-fitting choice for less than half of the market, which would lose business.

(In the real world, there are other considerations of course, such as the availability of connections if A and B have hubs at different ends of the route, crew and aircraft scheduling constraints and so forth -- so it doesn't always end up this way).

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    Do you have any evidence that this actually happens? Most of the time when I fly, my requirements are no more precise than "I'd like to depart in the morning", or "I'd like to arrive early enough to have dinner."
    – David Richerby
    Nov 2, 2015 at 21:46
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    @DavidRicherby Hotelling's Law doesn't mean your own (or anyone else's) requirements need to be particularly precise, just that the airline offers will tend to cluster at the average of everyone's requirements. Like how political parties all want the 'centre ground'. More-profitable passengers' requirements may be more influential, so the rqs of business travellers probably get greater weight on many routes.
    – A E
    Nov 2, 2015 at 22:27
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    In particular the example flights sound designed for business class travellers, who are likely not to want to miss a working day and also to have a much better chance of sleeping on the plane!
    – A E
    Nov 2, 2015 at 22:33
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    @AE Business travellers often dictate the schedule, because they are willing to pay more than the leisure travellers, and they also have more specific requirements.
    – Calchas
    Nov 3, 2015 at 0:46
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    @DavidRicherby Yes. I've written an extended comment on this answer as its own answer. I've also linked the corresponding wikipedia page, which mentions Jet Blue for being similar to competitors w.r.t flight schedules for exactly this reason (not a scientific source, but another indicator): travel.stackexchange.com/a/58242/16560
    – FooBar
    Nov 3, 2015 at 14:19
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There are actually quite a number of restrictions on flight timing:

  1. Airport noise regulations. Aircraft can't depart or arrive too late or too early in the day. When you take into account the restrictions in 2 airports, and add the flight time uncertainty of a long trans-oceanic flight, you may not have many time options left.
  2. Airport opening hours (many airports, especially smaller ones, are not open 24 hours a day)
  3. Passenger preferences. First, there's obvious preferences (like not departing/arriving in the middle of the night). Then there may be less obvious forces that shape demand, like the preferences of business travelers (typical business meeting schedules, etc). All this means that there may be a demand peak at a certain time, and any airline that deviates from that peak would lose out.
  4. Airline internal optimization. On the one hand, the airline wants to utilize the aircraft as much as possible - the plane is not making any money if it's sitting idle. On the other hand, there are minimum crew rest times (including union rules) and minimal maintenance windows. These factors are similar from airline to airline. When you take all these factors into account it may not leave much choice of times if you want to have an optimized schedule (especially if you want to have some regularity in the schedule).
  5. Schedule of connections in the departure/arrival airports
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    Maybe I missunderstood OP, but your answer's reasons more sound like they would justify why not one plane would leave at 8pm and the other allready 6pm. But OP's wording sounds to me like he is asking, why one leaves at 5.03pm and the other is leaving lets say something like +/- 5 minutes around it. But not even a big fraction of an hour in difference. And if thats what op is supposed to ask, none of your points gives a reasonable point IMHO.
    – Zaibis
    Nov 3, 2015 at 11:49
  • Thanks Zaibis...that is exactly what I was asking......for example right now UAL 839 and QFA 12 both left LAX at an STD of 10:30 and both are flying within a few miles of each other arriving at Sydney (one is a Boeing the other an airbus). 2 different aircraft leaving LAX and going to SYD. Both had the same departure scheduled time of 10:30pm PST. Granted their Scheduled time of arrivals were 15 minutes apart. I see this on both long hauls and regional flights(see earlier example of Air Canada an Westjet Calgary to Vancouver. I just wonder who and what dictates this kind of scheduling.
    – doug r
    Nov 4, 2015 at 20:55
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I'm going to basically add an extended comment to Henning's answer, who is spot-on.

Primer in Economics: Hotelling's Law

Avoiding product-differentiation can sometimes be optimal and is a very well-known phenomenon within Economics. It is more formally known as Hotelling's Law.

I'm going to introduce it here in the standard simplified environment, lemonade sellers at a beach.

Imagine a horizontal beach (on a straight line), where customers are evenly-spaced.

-----------------------------------------------------

Now there is two lemonade sellers, both indicated by x and y. The | indicates the center-point between the sellers. Every customer will go to the lemonade stand that is closer to him:

----x--------------------|---------------------y------

All the customers left to the center will go to x, the others to y. Note that if y goes closer to x, he will shift the center-point to the left, meaning that he will attract more customers.

----x----------|--------------y-----------------------

Yes, he is further away to some of his customers (the ones on the right end, but these have no alternative, so they will stick with them.

Of course, x will respond to movements of y and vice-versa. The only stable solution is where both are "exactly on top of each other", and share the customers evenly.

Back to Airplanes

Now, whether we observe this market phenomenon in reality depends on what I highlighted, that the customers have no alternative. So you should see this phenomenon happening more so on schedules with less competition.

Observe that we can also interpret the real line as time, and x and y as two scheduled flights at different times. One can translate the intuition one-to-one and will get to Henning's answer.

Is this a relevant mechanism?

Hotelling's rule finds application in many different settings, for example

  • distribution of political parties (on different topics)
  • large branded chains (having similar goods in terms of quality and prices)

The linked wikipedia page actually mentions the flight-schedule of Jet Blue as an example.

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  • Very useful and detailed answer, thank you! However, the following problem strikes me: The "stable" solution means that both x and y are an equally bad choice for their customers, who however don't have an alternative. This tends to build up customers' annoyance with both providers. At the same time, each provider only gets around half of its potential clientele, since they sit next to each other. How is this any better than the original situation - x at 25% and y at 75%? Then they have disjunct customer bases of around 1/2 the beach and are the better choice for their customers.
    – Mike
    Nov 12, 2015 at 21:34
  • Or, another way to look at it: The very knowledge of Hotelling's Law and the (stable, but bad) end result it produces should make both x and y refrain from such tactics. Also, the stable solution is only stable as long as no other competitor enters the field. If I were to jump into that business, I would not put myself in the middle next to x and y, but at 1/4 or 3/4 of the beach, thus creating a real alternative and value to potential customers, instead of just grabbing some random customers who still have no alternative, and who don't care if they buy from me or my competition.
    – Mike
    Nov 12, 2015 at 21:42
  • @Mike Collusion at a cartel is a similar phenomenon. Two firms could "agree" to keep the price "too high", above the competitive price. In this scenario they would both make more profits than with the competitive price.
    – FooBar
    Nov 13, 2015 at 5:22
  • @Mike Note that I didn't actually explain a "timeline", it's not the case that people start at 25-75, then 24-74 etc. I just showed that any other situation is "unstable", in the sense that both firms have strong incentives to change their flight schedule a bit in order to increase revenue.
    – FooBar
    Nov 13, 2015 at 5:24
  • Finally, yes, other competitors may be an issue. That's why I wrote So you should see this phenomenon happening more so on schedules with less competition.. Also note that in terms of revenue, while there are many customers all the morning, the business customers bring the largest revenue. If they are "in the left corner" (i.e. need to fly early in the morning), you will try to be as close to them as possible. The other, more flexible but less paying, economy class customers will then just have to adapt.
    – FooBar
    Nov 13, 2015 at 5:27
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I'll take a stab at this.

In the past, I've observed this as well, and I am sure that, at least sometimes, these are not codeshared flights.

On routes where many connections are available, this will come down to coincidence, but it can seem baffling when, say, the only two daily connections between two cities leave minutes apart, like in the example OP provides.

However, for all the examples that I remember observing, this was a consequence of the the two cities being best served at the times the flights connected them.

Specifically, in OP's example, UAL 98 leaves at around 10:30pm, and is set to arrive around 9:30am. QF 94 is set to depart at around 10:15pm, arriving around 9am. Obviously, by leaving at the end of the day, and arriving at the start of another day, the time 'lost' by passengers is minimised: if one of these flights would leave in the morning and arrive at night, the nights before and after, as well as the day spent in transit, would all be 'lost'. Now, the daytime lost in transit is minimised.

(Added:) Furthermore, if flights are relatively infrequent, a competing airline will know there's a market for a certain connection at a certain time, if a connection already exists. It then is easiest to simply offer the exact same flight as opposed to test the waters with a completely different departure and arrival time.

This is exactly the same reasoning that leads to medeaval cities having streets dedicated to one type of shop ('baker street', 'butcher street', etc.)

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    Good point MastaB....I see your logic on that Ozzie route....but I also see cases in my area that Air Canada and Westjet do the same thing. Airplanes leaving minutes apart ( say Calgary to Vancouver), arriving within minutes of each other and having several flights per day between said cities. current eg AC211 and Westjet 287.. (15 minutes apart in this case but often closer in departure and arrival times) I just wonder what factors go into such scheduling?
    – doug r
    Nov 2, 2015 at 19:45
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    @dougr the more flights two airlines have on a route, the more likely it is that competing flights will depart at close to the same time. For example, if an airline serves a route 8 times a day, assuming no flights leave between midnight and 6 am, there will be an average of roughly 2.5 hours between flights; if the flights are evenly spaced, a competing flight could be no more than 75 min. before or after. In practice, of course, the flights will cluster around convenient commuting times, as will the competitors, so most flights will be separated by even less time.
    – phoog
    Nov 3, 2015 at 3:50
  • Added some info on minimising risk.
    – MastaBaba
    Nov 3, 2015 at 12:33
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This is primarily a function of time zones and operational efficiency on the airline. Ideally international flights depart and arrive so that they can accommodate incoming and continuing connections from smaller local & connection flights. Obviously you also want to avoid the middle of the night in either time zone.

For example New York -> Frankfurt is served by Lufthansa, Singapore, Delta & United. The viable departure window for transatlantic flights from the east coast starts mid-late afternoon (super early arrival in Europe) to late night departure (airports shutting down in the US). Lufthansa actually captures the full window with three different flights at 4pm, 6m, and 10 pm. The other three carriers have a single daily flight almost at the exact same time (8pm). Lufthansa has a huge hub in FRA with lost of connecting flights during all of the day and for the US carriers 8pm is late enough to bring in most domestic connections.

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  • OK, so you've established that a certain route is somewhat restricted to flights in a window of about eight hours. That doesn't answer the question about why multiple carriers would have flights at very close to the same time. Also, Transatlantic flights are a special case: they use the North Atlantic Track system, which restricts departures from North America to Europe to happen in the afternoon/evening EST and departures from Europe to North America in the morning GMT. Airliners only cross the Atlantic in one direction at a time.
    – David Richerby
    Nov 2, 2015 at 21:52
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    @DavidRicherby It's also possible to leave the east coast early morning and arrive in Europe early evening (e.g., BA 178). But this means getting up early, losing a day of work and arriving just in time to go to bed. There's also little scope for feed at either end. These day flights are seriously unpopular.
    – Calchas
    Nov 3, 2015 at 0:41
  • @DavidRicherby It's not entirely true that airliners can only cross the Atlantic in one direction at a time. See, for instance, this timelapse of traffic data from NATS: vimeo.com/98941796, which shows a number of flights going "backwards". Only about half of flights in the region use the tracks. Airlines may not be able to achieve their preferred routes in the off-peak direction though.
    – Zach Lipton
    Nov 3, 2015 at 1:12
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    By way of example, BAW178, VIR26, and UAL934 all leave the New York area between 8:00-9am tomorrow for London, getting in around 7:30-8:00pm. They may not be super popular (though some business travelers may want to arrive the night before an important meeting), but compare those three flights to the ~two dozen scheduled to leave tomorrow evening. They may also help the airlines better utilize their fleets, avoiding having aircraft idle overnight.
    – Zach Lipton
    Nov 3, 2015 at 5:28
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    @DavidRicherby Even BA 1 with it's extended technical stop in Ireland arrives before 2pm usually
    – Calchas
    Nov 3, 2015 at 10:00
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Further to the already submitted answers, there is another reason why this may occur - the legal aspect, or collusion.

It is against the law for two companies to work together in order to reduce competition between the two. If Airline A was to speak to Airline B, and say "hey, you guys keep operating your 10am flight, and we'll move our flight to 2pm", then they would be falling fowl of competition laws.

A "joint venture" needs to be signed and agreed on by the relevant government authorities before two airlines can co-ordinate pricing and scheduling of flights.

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The main reason are probably the connections. Flights may have relevant connections that depart only at certain times at a day.

Especially when searching for a flight time that both matches with many connections before and with many connections after the flight, it is no wonder that options are limited and different airlines arrive at essentially the same timings.

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    Connections are generally with the same airline or, at least, the same alliance. So you're just pushing the question one level further back. Saying two airlines both fly from A to B at about the same time because of onward connections from B to C that depart at about the same time begs the question of why the two airlines' flights from B to C leave at about the same time.
    – David Richerby
    Nov 3, 2015 at 9:21
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Interesting question, and after reading all the answer, I noticed most forgot that the time and frequencies are actually dictate by computer.

What most airlines have in common? TICKETING SYSTEM!

Not only it is made for ticket booking, but also meant to calculate the cost and profit for a single journey, airplane optimisation, and also FLYING TIME based on input parameters (airport curfew, ground handling, catering, refuel frequencies, flying hours and on top of that MARKET RESEARCH which includes time preference, market demand, school holiday, etc).

Most but not all airlines are using A***LO (cant specifically named it, sorry) which is maintained by indian staff in Pune, India. So, doesnt matter which airlines is calculating or projecting one year flying schedule, they are normally come out almost similar as same parameters were fed in!

No single airline can cope with market research as it is global, hence most turn to a number of research house, YouGov, etc.

But, it is not final yet. You have to submit your planned timetable to the airport authority along with route taken to be fit in into their model, small airport maybe OK, but Heathrow with gaps of 45 seconds to the next landing plane? Or those in Australia with night-curfew? When these operators put into their patterns, then it will calculate again whether it fits with airport requirement and normally come out with minor adjustment - and these system dont discriminate airlines, they only recognise route, code, stack, estimated time and estimated fuel balance requirement.

Whilst the brand of the airlines maybe different and they are heading to the same place at almost the same time, but their planning system were all made and maintained by one company.

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    Why can't you name the system? Without being able to verify what you're saying, why should we trust any of it?
    – curiousdannii
    Nov 5, 2015 at 13:10
  • After 30 seconds of Googling, it seems clear that you're talking about a system called "Apollo". I don't understand what could possibly have been gained by censoring it like you did, as if it were a naughty word in a newspaper - if you're not allowed to name it for some reason, how is inserting a couple of asterisks really going to help you?
    – Nate Eldredge
    Nov 5, 2015 at 17:20
  • i did ask any one to trust what i said, and as Nate already did, Google has been helpful - I only gave the idea how the planning was done - and Nate gained more information by searching on Google. and because you cannot get the name of the system, you felt frustrated? then you have a long way to go! This information can be verified, not by the system name, but by having it vet by another person from this industry - which the way i see it, none so far. So, best bet for you is to print this and take it to any airline planning department.
    – Ed Nahar
    Nov 6, 2015 at 20:09
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Sometimes there are agreements between governments allowing each other airlines to fly between their state controlled air ports. These agreements must be fair, so both state owned airline can fly at the best times, therefore often both flight at the same time.

Even when the states have let go of some of the control, by then the “slots” at the airports are mostly taken up, so it is hard to change flight times.

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  • I'm marking this down, as I doubt you would be able to find a real world situation where this is the case. In reality, few airports are slot controlled. Even where they were, the chances of two airlines picking up slots at the same time, are pretty slim.
    – Gavin Coates
    Nov 4, 2015 at 21:30
  • @GavinCoates, I think it is common at Heathow.
    – Ian Ringrose
    Nov 4, 2015 at 23:50

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