I'm not going to bother reading the AAIB report, but I'm pretty confident that any contemporary rheumatologist would deny the AS link to inability to look out. If for no other reason than for most people it primarily affects the lower back. It smacks of lazy investigation to me.
Not as lazy as not being bothered to read the report of the death of a young air cadet on a pleasure flight
Nevertheless, we know that the spinal disease was progressive from 1970 onwards, and by the mid-1970’s, he had virtually no residual spinal movement, and although I have not seen a radiograph from that time, we do know that clinically he had very little neck movement, and the post mortem clearly described total fusion of the cervical vertebrae.