How awful. I knew David well. He was a lecturer at Bangor when I was there in late 1960s He took me flying in his Robin from Caernarfon in 2006 and I met him several times later including at a university reunion dinner in 2016 when he proudly told me about his new business advising clients about the accuracy of GPS. He was a very keen and conscientious aviator and this is a tragic loss.