According to a story this week in the Financial Times a new open skies agreement between the UK and the US might not be as straightforward as many in the industry would like. To quote one British official, "You can't just scratch out 'EU' and put in 'UK'."
The FT estimates that "the UK must renegotiate and replace about 65 international transport agreements after Brexit".
Potential difficulties lie in the simple fact that most bilateral air agreements require the participating airlines to be majority controlled by people from their country of origin. The existing US-EU air treaty requires the non-American carriers to be European majority-owned. After Brexit the UK will no longer be a subset of Europe and any citizen of, or organisation registered in, the UK will cease to be considered European.
The principle of majority control immediately raises issues for any proposed US-UK bilateral, especially for Britain's three largest long-haul carriers. Norwegian UK is not majority controlled by UK citizens and IAG's ownership is probably less than 50% British. Virgin Atlantic might still be 51% owned by Richard Branson but that is unlikely to remain the case if negotiations to sell most of his stake to Air France-KLM are successful.
Businesses have an excellent pedigree in transferring ownership to achieve commercial objectives but for airlines this can expose an inherent conflict. If substantial control of an airline rests in either the UK or the US, there is no longer sufficient EU ownership to qualify for EU 'open skies'.
In other words there is no easy way for UK carriers to retain the same route networks they now have. Lack of a UK-EU bilateral also means, as Michael O'Leary regularly reminds us, that EU carriers will not have the same unfettered access to UK airports that they now enjoy.
To all this must be added the fact that the EU-US arrangements contain anti-trust agreements which allow airline alliances and joint ventures to collude on fares and share revenues. Such an exemption will not automatically be part of any potential new UK-US agreement.
EU membership prevents the UK from signing any agreements before it leaves but this doesn't preclude conversations. However, at this stage the likelihood is quite strong that no British carrier on its own will be able to fulfil ownership requirements to enable them to operate both the short and long-haul schedules they now have after March 2019. Their full participation in joint ventures and alliances is also questionable.
This might have significant consequences for corporate air agreements which are dependent on volumes with existing partnerships which include a British carrier, such as Virgin and Delta. It may also mean that consolidating contracts and volumes for long-haul and European travel with a UK carrier, such as British Airways, is no longer possible.
President Trump last week heralded a trend away from free markets and towards protectionism when he announced plans for tariffs on steel and aluminium. This may compound the challenge for the extensive inbound and outbound UK traffic to continue seamlessly after Brexit unless the US agrees to continue to treat the UK as European during any transition period.
Carriers at present have enormous flexibility to fix route networks and capacity. That is in jeopardy.
Airline partnerships have taken away some of the complexity that used to exist in global air RFPs and air programmes. These are no longer certain.
Like many of the current US administration's positions, nothing is guaranteed.