Shapps does not have the power to make such a decision!
He told me on several occasions that there is no reason why the UK cannot be a non-EU EASA Member State such as Iceland, Lichtenstein, Norway and Switzerland currently are.
Those UK citizens who wish the UK to remain in EASA should write to their MP! Mine is Robert Courts; on 29th October 2018 he wrote:
You will be aware that the Government is seeking a comprehensive air transport deal with the EU which secures continued participation within the European Aviation Safety Agency (EASA) system.
He also wrote a footnote in manuscript stating:
P.S. Good to gear from you on this point; I hope this is reassuring.