Air travel: How will Brexit affect flight transits in the United Kingdom / London?

Suppose a traveler plans to fly between EE. UU And a non-European country on March 30, 2019 or shortly after, with a stopover in London (or anywhere else in the United Kingdom). The traveler is not a citizen of any current EU country (including the United Kingdom) but has permission to be in any of those countries from the perspective of the visa. This question is not about traveler's visas.

The UK is currently heading towards an effective "Brexit of non-treatment" on Friday, March 29 at 11 pm. For the purpose of this question, assume the trajectory of the status quo without announcing any important agreement, do not cancel Brexit, etc.

While Brexit may not have an impact on the visa problems for the scenario in this question, it seems reasonable to believe that it could affect the aircraft availability/ fuel / supplies / etc. to enter the United Kingdom on incoming flights from the EU and then be available for the connection exit. Even if it were possible to find from where the departure flight is scheduled, airlines could be making a lot of last-minute detours due to restrictions in other parts of their systems.

With Brexit starting on Friday night, it is likely that many government, regulatory, insurance and airline offices that may have answered questions are closed for the first two days.

The quartz explains:

unlike other industries, which can resort to WTO agreements to regulate trade in the event that existing agreements cease to exist, the aviation industry does not have an alternative plan. That means that in the case of a Brexit without an agreement on March 29, there will be no regulatory framework on which flights can operate from the UK to the EU on March 30.

Ryan Air will offer refunds of flights if the regulatory environment requires the cancellation of flights, and does not foresee overnight stops on flights, why has established new subsidiaries, but

The representatives of easyJet and IAG, the parent company of British Airways, told Quartz that they are not making contingency plans for the event that there is no agreement … easyJet said he is confident that "consumers, Airlines and politicians from across the UK and Europe I want the flights between the UK and Europe to continue. "

A BBC article notes that without agreement, aircraft with British-made parts will be grounded even in places like the US. UU And China due to the lack of valid EASA safety certificates, as another way in which the availability of aircraft in the United Kingdom may be limited (although my understanding is that parts previously certified as valid could remain in service; wrong).

The Independent reports that "flights will continue, but not necessarily to the same extent."

The UK Government's "no agreement" guide (which is covered here in the announcement) reads as follows:

The United Kingdom has independently negotiated 111 bilateral ASAs with countries around the world, including China, India and Brazil. There are 17 other non-EU countries with which air services are provided to the United Kingdom by virtue of our membership in the EU. These are Albania, Bosnia and Herzegovina, Canada, Georgia, Iceland, Israel, Jordan, Kosovo, Liechtenstein, Macedonia, Moldova, Montenegro, Morocco, Norway, Serbia, Switzerland and the United States … For airlines from one of the 17 countries that are not The EU countries with which air services to the United Kingdom are currently provided by virtue of UK membership in the EU, replacement agreements will be in force before the departure date.

He says that it would be necessary to grant new permits / agreements and that without such permits, "there could be interruptions in some flights". The government's page remains optimistic about the prospects of an agreement to allow air traffic to continue, including a "simple" agreement that the European Commission indicated could help ensure basic connectivity, but still requires airlines to apply and receive the approval of several. permissions; EASA is not currently accepting such requests from UK airlines (according to the UK government page).

The guarantees that the arrangements will be in effect appear to have not changed since September 2018, but there does not seem to be any solid reason to rely on those guarantees without contingency planning for the current trajectory. "Just be optimistic and trust that governments will draft an agreement that has not been implemented at the time of this Response" seems to be an unsatisfactory answer to this question, even if it is the official line of the UK government at the time This question is published.

Assuming a status quo path from the moment a Response is published / updated, How will Brexit affect flight transits through the UK currently scheduled for shortly after Brexit? Recognizing exclusions in travel insurance policies, Are there effective ways to ensure / mitigate these negative results?

A mitigation strategy that some people (who have not yet booked a trip) may consider reserving a transit through a non-UK city. The effectiveness of this strategy (especially related to Brexit that limits the availability of aircraft) can also be discussed in Answers, since it is practically the same problem with the same cause.

This question will remain open to new answers without an Accepted Answer until after the Brexit, inviting good responses, especially by citing authoritative sources for votes earlier.