With two helicopters on lease to HM, The Queen, the cost of the lease is paid regardless whether or not the birds ever leave the ground. HM, known to be frugal, examines the reason for the use of a helicopter, who is using it and where it is transporting to or from before it gets the royal assent.
It is often the complaint that other means of transportation could have been used but do those that complain actually stop and think that perhaps another mode of transportation (such as a public train line) would casue more problems than be a convenience such as security, disruption to the public etc?
I'm happy that the two of them were able to just fly off to Sandringham and have the shortest trip possible between the two places. I can imagine that even with colds, both HM and the DoE feel much, much better being "home" for the holidays and all is as it should be.
Come to think of it, the only time I can really remember seeing HM get into a helicopter was for her grand entrance into the London Olympic Games of 2012 with Daniel Craig. I will never, ever forget that. Classic.