Before I bought my Aeronaut recently, I researched the four budget airlines that I fly with most often, and one more that I may use, in order to see which of the three principle Tom Bihn travel bags were compatible with the allowances. I thought that this might be interesting for others who may be contemplating some European travel in the near future.
I should say that, in the main, these are all similar to the 45" rule (115c.m.), but here they are very strict about the ratio of the lengths e.g. Ryanair's 55x45x20 is 115c.m., but if you turn up with a bag 50x50x15 or 55x35x25 they will make you check it - and charge you. Anything close will be tested and your bag may also be weighed and one kilo over will not go down well! All of these airlines limit you to 10kilos (22lb). And its strictly, absolutely one bag, nothing extra. A friend tried to get on a Ryanair flight in January with a cup of coffee in her hand. She had two options; ditch the coffee, or put it in her bag. She put it in her bag with inevitable consequences!
Note all of the airlines use those metal framed testers. Some, however are vertical in operation (e.g. Ryanair, Flybe) so height and depth are more critical, whereas others are horizontal (e.g. Easyjet, Jet2) so length and depth matter more. Always depth matters most so don't over pack.
On the plus side, and the reason I went for the Aeronaut, despite what you're just about to read, is that all Tom Bihn bags, and especially the Aeronaut are squash-able, and therefore I hope it can be squeezed it to the baggage testers so long as its not over stuffed. This wouldn't be the case with rigid cases. I'm flying with Easyjet on Wednesday, which should be fine, as they are the most generous, but while I'm at the airport, I intend to try all of the size testers out. I'll try to get photos, but I believe its frowned upon to take photos in the airport so we'll have to see.
Although Flybe is the most restrictive, to date they have been the least strict about enforcement. Last time I went with them, I had an overstuffed 30 ltr rucksack that wouldn't have gone near their tester simply because of its round section, plus I had my iPad Ristretto (a second bag is an absolute no-no here) and not only did no-one stop me, but the hostie put it in the bin for me.