Did anyone nominate him this time round? It's my understanding that, apart from civil servants, the rest of us need someone to nominate us for an award.
Anyone, including Civil Servants, needs to be nominated. The basics are on the Gov website
https://www.gov.uk/honours/overview . Surely there are people in the services and professional bodies for test pilots who could make a convincing case for Winkle Brown. Do they need prompting?
It may of course be that, as suggested by Alan Lupton, an honour has been offered and rejected.