In order to run an airline in this country or anywhere else in the territories of EU Member States, operators must hold an air operator certificate (AOC). These certificates are issued by the "competent authorities" of EU Member States, under the authority of Regulation (EC) No 1008/2008 on common rules for the operation of air services in the Community. A holder can then operate anywhere in the EU.
Come Brexit, therefore, holders of AOCs issued by the UK "competent authority" will no longer be valid in the European Union. This will not require any action on the part of the EU. Simply, according to the definitions within Regulation 1008/2008, an "operating licence" has to be granted by the authority of a Member State. The UK will not be a Member State, so its certificates cannot be valid.
However, this is not a REACH-type situation, where no action can be taken until Brexit kicks in. Operators such as EasyJet are already on the case. Their reasoning is that they can set up shop, with a skeleton team, in any other EU Member State and apply for an AOC there.
While this will keep the airline operational in EU Member States, it leaves the UK out on its own. It is assumed that, by the time Brexit kicks in, the Government will have converted its EU certificates into permissions to operate in the UK. Clearly, that is the limit of their scope as, outside the EU, UK-issued certificates will confer no rights in Member State territories.
That would mean that the eventual outcome of Brexit will be that those airlines which currently operate throughout the EEA will have to hold two AOCs – one for the UK and another for the other territories. An alternative would be for the UK and EU to conclude an agreement on air transport, similar to that of Switzerland, or build it into an over-arching free trade agreement.
A failure to reach an agreement, or where Madam May exercises her "walk away" option, could require emergency administrative action on the part of the UK Government, simply to regularise the operations of UK-based airlines.
Here, one assumes that the Government would look to rely on the Great Repeal Act, repatriating Regulation 1008/2008 and giving it legal effect in the post-Brexit environment. As with the Union fishing legislation, though, simple transposition would not be of any value. The regulation sets up a community system for the management of civil aviation, which could not be shoe-horned into UK law without a very substantial re-write, if an effective UK system was to emerge.
This is particularly the case as Regulation 1008/2008 deals not just with airline licensing, but also with market access; aircraft registration and leasing; public service obligations; traffic distribution between airports; and pricing.
The issue of market access was brought up by (then) Prime Minister David Cameron before the referendum, in an authored piece in the Telegraph. In this, he posited a scenario where British airlines were no longer allowed to fly between Rome and Paris, as a consequence of us leaving the EU.
What he was actually referring to was the sixth freedom which permits a UK-registered airline picking up paying passengers in Rome and dropping them off in Paris, or vice versa, when en route from a UK destination.
The first five freedoms, which include the right to fly to and from a foreign county, the right to overfly others, and the right to refuel or carry out maintenance in a foreign country without embarking or disembarking passengers or cargo, come as part of the package written into the Convention on International Civil Aviation of 1944, otherwise known as the Chicago Convention.
The so-called "sixth freedom", through to the ninth, are known as "beyond rights", which do not come automatically. They must be negotiated and agreed separately between individual members of the International Civil Aviation Organisation (ICAO) or, in the case of the EU, between Union Member States.
As they apply to EU Member States, they rely on Regulation 1008/2008, including the "ninth freedom" which allows a service to be performed by an airline certified in one Member State, entirely within the territory of one of more other Member States - also known as "stand alone" cabotage.
It is this freedom which allows airlines such as RyanAir, based in Ireland, to provide services in other Member States, including, of course, the UK, without their aircraft having to return to Ireland as part of each flight.
Clearly, post-Brexit UK legislation can permit EU (or EEA) airlines to operate in the UK, but it cannot require UK-based aircraft to be given the same level of freedom within EU Member States. Rights and freedoms would have to be negotiated as part of a treaty package but, if Mrs May goes walkabout, airlines operating out of the UK could find themselves severely limited in the services they could offer.
In that event, EU-based airlines would also encounter limitations on services to the UK, leading to fears (especially in Ireland) that some routes could be discontinued. There have certainly been suggestions that RyanAir could cease flights within the UK.
For all that, we've only referred to one set of regulation. In all, I count over 40 pieces of legislation, ranging from laws on insurance requirements for air carriers and aircraft operators [Regulation (EC) No 785/2004], on the code of conduct for computerized reservation systems [Regulation (EC) No 80/2009], rules for statistical returns [Regulation (EC) No 437/2003 and Commission Regulation (EC) No 1358/2003], air services agreements with third countries [Regulation (EC) No 847/2004], and much, much else, including the allocation of airport slots [Council Regulation (EEC) No 95/93].
Of particular relevance is the establishment of the European Aviation Safety Agency [Regulation (EC) No 216/2008], rules for the airworthiness [Commission Regulation (EC) No 1702/2003 and (EC) No 2042/2003] and, of course, the Single European Sky, covering the provision and development of air traffic control services.
In attempts to repatriate the 74-page Regulation (EC) No 1702/2003, for instance, the Government will find a task more complex than the fishing regulation.
The 114 references to Member State (singular and plural) provide more than adequate testimony as to their purpose. Tied in with 190 references to the European Aviation Safety Agency, it is clearly evident that even extensive re-writing will not provide a workable legal base for re-establishing a UK airworthiness certification system.
Experienced voices suggest that EASA is here to stay. With our commercial interests in Airbus, we are not in a position to start out anew. But May on her "walkabout" would peel us away from EASA and precipitate a major crisis. Repairs and routine maintenance, and the certification of UK-made parts, would be as badly affected as manufacture.
Says Jeegar Kakkad, chief economist for ADS, the trade body for the UK aerospace sector, "Maintaining access to the certification regime in Europe is absolutely critical, as there is no UK replacement that can get up to speed quickly enough". As Pete pointed out earlier, he thinks that if the UK were to assume safety and certification responsibilities - as it did before the creation of EASA in 2002 - it would take ten years to re-create the necessary infrastructure.
Nevertheless, with such a multi-faceted industry, it would take a brave man to predict where the cracks would first start to show. Aviation in all its sectors is extraordinarily resilient and flexible, capable of dealing with most of what politicians can throw at it.
Like chemicals and pharmaceuticals, it is far too valuable needlessly to destroy or abandon, so any squeals of pain are likely to be heard and acted upon.
From even this brief overview though, rapid, enforced cleavage from the EU, on the "walk away" model, clearly is not an option. The complexity of the issues militates against concluding a free trade agreement in the time and the Great Repeal Bill is unlikely to afford any relief.
Gradually, I expect, more details will emerge on potential threats and avoidance strategies, from which – we can but hope – policy coherence will emerge, if only because it must. But if this is to happen, it must do so soon. Yet there are no signals that would suggest we have reason for confidence. Time is not on our side.