The only question that matters is, was flight safety compromised directly as a result of the pilot`s disability. This must be considered by applying the question in the opposite sense, had the pilot not been so disabled as to be reliant on a prosthesis, would this event have occurred.
Had the event led to a serious accident what could the position of his employers be. I think short of pleading a defence as an equal opportunities employer under the Equality Act 2010, it could well have turned out a bit of a sticky wicket for them.