Very sad news.
He was a great character as well as a great figure in motorsport.
As Heliport says, he had a keen interest in aviation and wanted to actively support a British engineering company after he left motor racing, hence his involvement with Pegasus. I knew him slightly through that connection and always enjoyed meeting him, the final time being in the summer, sitting in his garden while he gave me a good-natured ribbing about what to expect from married life not long before my wedding.
RIP Keith.