The following companies are/were all big and are/were now in trouble:
SABENA
Enron
British Leyland
BCCI bank
Barings Bank
Pan American Airways
etc.etc.etc.
Being big does not mean you are safe - it may just mean that your organisation is clumsy and slow to react to change or indeed just highly exposed to market forces.
I don't know if OATS are in trouble (but I would be surprised if they are not hurting) but it is a pretty fair bet that the real estate ax Kidlington is worth more than the business OPATS can bring in.
I hope they do not go down (I don't expect they will) - but it is not impossible. I do, however, expect them to suffer for a while as we all are doing at present.