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The India-Pakistan feud has heated up again, with Pakistan closing its airspace as a result.

I know many international routes fly over Pakistan, and that the closure would cause issues, but this report surprised me:

Thousands of people were also stranded by affected airlines that not only land in Pakistan, but fly over its airspace -- one of the major routes from Southeast Asia into Europe.

Thai Airways announced that all its European routes "departing near midnight of 27 FEB through early 28 FEB" were canceled "due to sudden closure of Pakistani airspace as a result of tension between India and Pakistan."

Why would the airspace closure force flights over it to cancel entirely? I would think you would just reroute them around it.

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    $\begingroup$ Travelling through the middle east is not easy, not even above the skies. There are several closed airspaces and a few you want to avoid due to terrorism and an increasing capacity to hit high altitude targets. $\endgroup$
    – Stian
    Commented Feb 28, 2019 at 18:07
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    $\begingroup$ Consider the fact that all flight routes that were planned had to be handed in again and be accepted. Changes result in necessary fuel and new time slots for takoff and landing airport. This has to be recalulated and might take some time $\endgroup$
    – Lumis
    Commented Mar 1, 2019 at 12:44

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To give an example of how flights can be affected by this in ways to make them impossible, Iranian airspace is closed from sunset to sunrise (unless things have changed recently). Any aircraft that due to the closure of Pakistani airspace would need to cross Iranian airspace and be unable to do so because of that closure now needs to be cancelled or rescheduled.

Also, if the diversion around Pakistani airspace would stretch the endurance of an aircraft beyond what fuel it can carry, it cannot fly the route.

Or the diversion would cause such a delay in the schedule that it causes too much problems with the overall scheduling of the airline. Such things tend to have a ripple effect. One flight gets delayed by several hours, dozens of others get delayed as a direct result, hundreds more can suffer delays in the end.

Also, some airports only operate during daylight hours. A diversion around Pakistan might mean the flight can't make it to one such airports before sunset and thus can't land at its intended destination. Now the airline has 2 options, divert to another airport, arrange for bus or train transport for all the passengers, and in the morning yet another hop to the intended destination to pick up the new passengers, or cancel the flight.

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  • $\begingroup$ Or the airport doesn't operate late nights, such as SYD. $\endgroup$
    – Michael Hampton
    Commented Feb 28, 2019 at 15:29
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    $\begingroup$ * Iranian airspace is closed from sunset to sunrise * I might be wrong but I see many landing scheduled at night there $\endgroup$
    – user189035
    Commented Feb 28, 2019 at 16:32
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    $\begingroup$ I would love to know more about Iranian airspace, maybe I'll post a different question. Flight paths over Iran, Iraq, and Afghanistan are typically restricted to one of a few routes. $\endgroup$
    – zymhan
    Commented Feb 28, 2019 at 16:38
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    $\begingroup$ @JohnRay: MH17 didn't involve any buffer zones - it was shot down while flying directly over an active warzone. $\endgroup$
    – Vikki
    Commented Mar 1, 2019 at 4:31
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    $\begingroup$ @Sean - Sorry, I meant that since MH17 airlines now want to leave a large buffer zone around any conflict areas. $\endgroup$
    – John Ray
    Commented Mar 1, 2019 at 16:18
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Not mentioned in the other answers is simply logistics coordination. If you can't fly over Pakistan, that suggests that maybe you have to fly somewhere else. Perhaps flying around means an overflight of China or Kyrgyzstan. Do they charge overflight fees? Do they require prior permits? Even if the money involved isn't huge, starting up a new route may mean the first time your airline had to work with that country. I'd expect that could take a few days.

Even if you already have a relationship with the country from other routes, adding permits and having the accountants approve the route choice would still be required.

https://www.jetex.com/overflight-fees-in-asia-pacific/

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    $\begingroup$ Interestingly, right now Thai Airways is largely flying over China, Kazakhstan, Russia, and Belarus, while EVA Air is using a route over India, the Arabian Sea, Iran, and Turkey. This speaks to the fact that logistical factors will differ between airlines, and different decisions will be made. $\endgroup$
    – Michael Seifert
    Commented Feb 28, 2019 at 17:54
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    $\begingroup$ It also appears that Thai Airways avoided Iran even before the Pakistan closure. This may be because Iranian overflight fees are relatively expensive. $\endgroup$
    – Michael Seifert
    Commented Feb 28, 2019 at 18:07
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There are multiple reasons for cancelling instead of rerouting:

  • Take-off & landing slot assignments
    • You may have a pair of slots available and your regularly scheduled flight uses them. Rerouting the flight will take longer and you may no longer make your destination landing slot
  • Departure & arrival gate assignments
    • Likewise, you may no longer have a gate assignment available at the destination airport because the reroute takes too long.
  • Aircraft range.
    • If your flight is near the maximum range by overflying Pakistan, rerouting around it could push the plane past its maximum allowable range.
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  • $\begingroup$ If range is the problem, why not just make a technical stop somewhere like India or Iran? $\endgroup$
    – Vikki
    Commented Mar 1, 2019 at 4:05
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    $\begingroup$ @Sean it's not so simple. You need to arrange the landing and take-off slots, you also increase costs and schedule significantly. $\endgroup$
    – Ister
    Commented Mar 1, 2019 at 9:05
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There was an extensive report on the grounding of Thai Airways flights in The Guardian today. To quote:

Thai Airways said later on Thursday it would resume flights after gaining permission from China to use its airspace for nearly a dozen flights to Europe set to leave on Thursday afternoon and Friday morning.

Quite simply, Thai lacked the necessary permissions.

The Chicago Convention on International Civil Aviation established a general right for overflight by foreign aircraft, but many states nonetheless require airlines to acquire permission in advance – including China.

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  • $\begingroup$ Why not fly over India and the Arabian Sea instead? $\endgroup$
    – Vikki
    Commented Mar 1, 2019 at 4:04
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    $\begingroup$ That would also explain why certain airlines, most notably the Taiwanese airlines China Airlines and Eva Air, don't fly over PRC airspace. Given the political sensitivity between the two countries at the moment and the pressure the PRC is imposing on airlines regarding the wording of Taiwan, it's highly doubtful that any Taiwan-registered airline would ever be granted permission to use PRC airspace. $\endgroup$
    – Michael Dodd
    Commented Mar 1, 2019 at 11:40
  • $\begingroup$ @Sean: I noted in my comment on another answer that Iranian overflight fees are relatively expensive, and Thai Airways avoided Iranian airspace even before the closure. If you don't want to overfly Iran, and you don't want to overfly the Middle East, then going towards the Arabian Sea doesn't help you that much. $\endgroup$
    – Michael Seifert
    Commented Mar 1, 2019 at 13:51
  • $\begingroup$ @MichaelDodd Taiwan-based airlines operate regularly scheduled flights between Taiwan and PRC airports. I wouldn't be so sure overflight would be restricted. $\endgroup$
    – cpast
    Commented Mar 3, 2019 at 0:17
  • $\begingroup$ @cpast I may be mistaken, or at least the situation may have changed since I last flew to Taipei. When we visit my wife's family our usual choice of flight is China Airlines CI70, with CI69 as the return flight. While CI69 still flies past Japan and over Russia, arguably taking a longer path to avoid Mainland China, CI70 does seem to skirt the Southern PRC on its way to the Hong Kong ATC waypoint. $\endgroup$
    – Michael Dodd
    Commented Mar 3, 2019 at 10:17

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