Old Akro
I don't wish to be contentious but limited neck movement is a very common symptom for AS sufferers, including me - this was certainly a major factor in the unfortunate collision between an RAF Tutor and a civilian glider.
King8888 - don't give up flying yet! It may be forced on you one day if you are unable to pass your Class 1 medical. This happened to me in 2000, aged 53, and I was medically retired from my job as an ATCO at LHR.
NASS ( the UK AS society) has constantly denied a link between diet and AS. For what it's worth I have found that anything that upsets my stomach triggers an AS 'flare' and vice versa. I am one of the 15% of the population who can not take 'normal' NSAIDs because of stomach bleeding and possible ulceration. I have found the newer COX2 NSAIDs to be less harmful to my stomach but I still take a stomach protector tablet ( Omeprazole) as well.
I also take a good probiotic every day as well as Aloe Vera liquid and avoid cow's milk products as much as possible. I do not eat meat but am unsure if this has any benefit re AS - it's just a personal choice.
I cycle as much as possible but it does exacerbate neck pain, as does swimming. Avoid contact sports - the risk of damage to fused bones makes it not worth it!
Long haul flying will be difficult, unless you can get up and stretch every hour or so. I find sitting for any period longer than 30 minutes quite painful.
Hope this helps, PM if you need any further advice.
Good luck with the career!