Not all airlines follow this sequential pattern. Some are more scattered – and of course, it is not as easy when fleets keep changing. And some airlines have taken a more light-hearted approach. Icelandic airline WOW Air, for example, chose a lovely family series for some of its A320s and A321s – with registrations TF-SIS. TF-BRO. TF-MOM, TF-DAD, TF-KID, and TF-SON (TF is, of course, the prefix code for Iceland).