As a sufferer of Ankylosing Spondylitis I find this report so sad and, am absolutely amazed that the pilot was not only permitted to continue flying but was foolish not to retire voluntarily.
My Class 1 medical, which is a basic requirement for a licensed ATCO (no medical = no licence), was withdrawn in 2000 when I was aged 53 at SRG Gatwick by a visiting specialist. He was in fact a serving RAF doctor of Group Captain rank, later an AM I believe. His take was that due to my limited mobility, similar to the pilot in this case ie poor neck movement and sideways flexing at the hips and,in my case associated constant fatigue,it would be unsafe for me to continue, particularly as I worked in the tower at LHR.
At my 2 or 3 previous annual medicals with Doc Morgan, retired aviation medicine specialist at Boscombe and CAA licensed doctor,he had told me that had I been a pilot he could no longer continue to sign me fit. He thought that I would not have been able to cope with extra loading of flying controls in various emergencies.
The examination at Gatwick had come about because my GP and Rheumatologist were sure my health would be better if I retired.
As for the 'burn out' mentioned in the report, this is a bit of a misnomer because, although the sufferer may no longer have any active symptoms of AS, the fusing and calcification is there forever.