Antigonads - So how do planes from countries not in the EU manage to fly?
This is a good example of some of the issues around Brexit, there are literally thousands of others.
International Air travel is tightly regulated by a number of International agreements to which countries have to adhere to (nothing to due with the EU). Now the responsibility for regulation is with the local regulator.
Now the local regulator for the UK is EASA (European Air Safety Agency.
After Brexit we will not be part of EASA so the CAA will have sole responsibility.
But the CAA does not have the staff, or expertise in a number of areas. Nor has the UK signed up to a number of Air Safety/Travel Agreements such as Open Skies. Until those are in place, then yes we could see UK aircraft unable to fly outside of the UK.
Essentially the CAA needs to duplicate what EASA does but all the cost is born by the UK.
This is a huge deal, not just for air transport but also for the Aerospace industry which employs hundreds of thousands. Each part has to be certified by the regulatory authority. As it stands the CAA is not considered competent (nor it seems is receiving sufficient funds to make it so) so won't be able to certify parts.
This has led to Rolls Royce shifting some jobs and work to Germany so it can still get it's jet Engines certified by EASA. For smaller firms, this may not be an option.
It's a mess, and this is just one small example, there are thousands of others.