I think the extraordinary circumstances advanced by BA cannot succeed in court. They will have to justify why on a specific date and a specific route some flights were grounded and others not. What specific criteria were used by BA to cancel the flights ... medical or economic? or cancelling mostly short haul flights while maintaining long haul flights ... there is the element of discriminatory measures taken by BA ... probably deliberately favoring yield maximization ... all these are, in my opinion, difficult to justify as "extraordinary circumstances".