Very sad news. I first met him at Helitech in 1989, where he was commentating on the air displays (the year the Russians came to town!). I had a few written exchanges later and bought the first edition of Cyclic and Collective directly from him. I was honoured when he sent me a CD with his updated edition, a few years later, and asked if I could make comments. Met a few times after at HAI. Really nice guy.