Speculation
So much speculation. It is fun but it will be a while until we get the facts and maybe not ever.
One thing I'd like to add. If the whole of the BA fleet was grounded because of a failure in a major plane component such as the engines (reliability, safety or such like) there would be a huge shitstorm and the supplier would be severely damaged (financial and reputation). We seems to accept these IT failures with a shrug albeit an angry shrug. I think this is because we expect IT systems to fail an experience shows we are right.
Biting the hand that feeds IT
