My understanding of racial discrimination law is that although one might argue that the withdrawal of staff travel discriminates against cabin crew who live in those more far-flung places who're more likely to be of other races, it would be a form of indirect, rather than direct, discrimination.
And whilst there is no defence for direct discrimination, if indirect discrimination can be justified it is allowed.
For example, a requirement that cabin crew not have a beard indirectly discriminates against Sikh men, but it can be justified on the basis that a beard interferes with the fit of a smoke hood and a court would not have a problem with it.