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I am trying to book a one way flight from Frankfurt to Delhi. While checking the Vistara official website I noticed that on two separate date 02.10 and 16.11. the flight is taking 08 H 40 m and 09 H 50 m resp. Both flights are taking same aircraft Boeing 787-9. Has the website confused because of daylight saving. Here is the screenshot of the booking for both dates:

02 Oct

16 Nov

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    I can't think of another reason than a DST-related glitch. Sep 28, 2023 at 10:42

3 Answers 3

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It's most likely operational.

The change coincides with a daylight savings time change in Germany on Oct 29. For any DST change the schedule needs to be adjusted. They either have to move the departure one hour forward or the arrival an hour backwards. Which one they choose depends on a lot of factors: connections, crew availability, maintenance intervals, etc. Another big one is availability and cost of departure and landing slots at the airport.

In this case I'm guessing Vistara looked at the schedule, decided to keep their departure slot in Frankfurt (which is a busy and expensive airport) and adjust in Delhi. They may have decided to go extra slow either because they couldn't get a better landing slot or for fuel optimization (or some other operational reason).

enter image description here

The other major airlines on this route are Lufthansa and Air India which both only take 7:35-7:45 so after the DST change Vistara is more than 2 hours slower than the competition. If someone is interested: here is a table how all three airlines deal with DST

enter image description here

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    This begs the question why aren’t all time slots for take off and landing booked in UTC? Worst case is that local times will shift, but flights will always be the same length and they won’t have to rearrange slots.
    – Darren
    Sep 29, 2023 at 7:21
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    @Darren: Because locals -- and local flights -- don't give two figs about UTC. They think local time, they use the local time in their daily life, they book meetings and taxis in local time, etc... Sep 29, 2023 at 7:39
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    @Darren And even if you did schedule the slots in UTC, you'd still have to change the slots at the beginning and end of the day because noise management rules and airport opening times tend to be in local time, and that cascades across the day. Sep 29, 2023 at 15:13
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I don't think this is a glitch, as least not in the sense "website does not show correct times or duration because of DST change".

When time changes at either end of the flight, airlines have to adjust their timetables, and with additional considerations such as night curfews (not applicable here, but could be applicable to other flights, which would have a knock-on effect on aircraft or crew planning and availability) or connections to other flights, it often happens that they make significant changes to their whole schedule (not just that flight). They may also take that opportunity to add or remove destinations or flights.

So they will end up basically re-planning their whole schedule.

Now there could be several reasons they decided to plan more time for that flight:

  • They noticed they were often late (not saying this is the case here, I haven't looked at the history), so decided to add some more buffer (remember, this is a scheduled time, the flight may well arrive much earlier than the schedule). For flights from Europe, this is especially important due to EC261 compensation they may have to pay out for delays, particularly if there are onward connections.

  • They couldn't get matching departure and landing slots at the two airports, so they had to adjust one.

  • Seasonal weather patterns may affect winds and/or routing.

  • They had to change their usual routing due to geopolitical considerations (wars) but hadn't updated their schedule until now.

  • They want to save fuel (not convinced at all this actually works out -- probably a good question for aviation.SE).

There are probably quite a few other reasons that haven't come to mind.

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As this difference appears exactly after the daylight saving hour change

enter image description here

and has apparently not any other logic reason (same A/C, no stops, all the same) I'd say that it's just a glitch caused by the daylight saving.

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    Even if that coincidentally is the date of the DST change in Germany, the airline is also both changing the time of departure and the time of arrival. The difference in flight time is also not 60 minutes, as would have been expected if it was a DST related glitch, but 70 minutes. I don't know the reason for the schedule change, but this explanation does not seem reasonable. Sep 28, 2023 at 10:59
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    @Tor-EinarJarnbjo How about this: Airline changed the departure time (coinciding with the DST end), probably the flight will have to take a slightly different path and that explains the additional 10 minutes. The rest is a DST-related glitch. Sep 28, 2023 at 11:03
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    @Johnnyjanko I am not at all convinced. A just as likely explanation is that the airline isn't able to obtain an earlier landing slot in Dehli and therefore decides to fly slower and save fuel. The other airlines flying directly from Frankfurt to Dehli (Lufthansa and Air India) also have a change in schedule on the same day and Air India is flying a bit faster after the change. Sep 28, 2023 at 11:13
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    @gerrit Schedules are transmitted in local time of the airport, because thats what the airports use, and its more important people get to the airports on time, than that the flight time is processed correctly. Sep 28, 2023 at 12:18
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    It coincides with DST switch but it doesn't appear to be a glitch since it persists. DST is the trigger but not the root cause here.
    – Hilmar
    Sep 28, 2023 at 12:32

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