The European branch of Airports Council International (ACI Europe) has warned that passengers will be hugely disrupted if an agreement isn't reached by the two-year Brexit countdown.
The UK's air traffic is predominantly with the EU, as more than one in two passengers travel between the UK and EU.
Failure to reach an agreement within the strict two-year deadline for negotiations, to be started when Theresa May triggers Article 50 on 29 March, would mean the UK exiting the EU without the terms of its new relationship with the bloc being clearly set out.
This could cause huge disruption for air connectivity and the economy, if market access falls back on more restrictive bilateral provisions between the UK and individual EU member states.
ACI Europe has urged negotiators to prioritise the industry, highlighting the interdependence of both markets.
It noted that 53.5 per cent of passengers handled by UK airports are flying to or from the EU27 and 11.5 per cent handled by EU27 airports are flying to or from the UK, also reflecting UK airports are, on average, far more dependent on air traffic to and from the rest of the EU than vice versa, though this does vary across different places.
Olivier Jankovec, director general of ACI Europe, said: "The contribution of aviation to the economies of both the UK and the EU27 is largely conditioned by the full integration of their aviation markets - enabled by the Single Aviation Market.
"Let’s be clear: losing this integration between the UK and EU aviation markets is akin to putting an end to a relationship which creates tremendous value and brings extensive mutual benefits."
Unless quickly resolved, this uncertainty will end up constraining route network development for airports, ultimately affecting air connectivity for their communities. This is due to the fact that airline route planning requires both long lead times and legal certainty.
Earlier this month, aviation minister Lord Ahmad told the industry it would be needed "more than ever" with Brexit on the horizon.
He repeated comments made by transport secretary Chris Grayling, saying it was in the interests of the UK, the EU, European countries and everyone who lives or travels between them, to seek "a liberal arrangement for aviation".