Interlining is one of the most important features of any itinerary that is more than just from A to B and back. It is also something that is in grave danger. In the good old days :-) getting around three of four places was quite simple. It may not have been that cheap but it was simple. The old paper ticket meant that you could check through all your bags from where you got on to where you wanted to get off without having a load of jiggery pokery in the middle - and that irrespective of who the airlines involved were. Along comes E Tickets and life starts to get difficult. First off, airlines are suddenly able to decide who they want to be in bed with. Whereas before they all had to be in th same IATA pot, now they can pick and choose. And pick and choose they do - to the great disadvantage of the global roamer. Why does this make life difficult? The main principle out of the window, is that of the minimum connecting time. This is the amount of time that had to allowed for you to connect between any two given flights at any given airport. As long as you complied with this, if you missed your connection, you were the airlines problem and they had to sort you out, one way or the other.

Along comes E Tickets and Oooops! The airlines you need no longer allow interlin E tickets with all and sundry.Only their mates. This means that you have to land, collect your bags, go through customs and re-check-in for your next flight. This makes none interline eticket  flights a thundering nuisance. It also tries to get you to stick with one carrier - and as we all know that is not always possible or desirable, even. The other issues neatly cleared up is as you are no longer on one ticket, each flight becomes a seperate entity - so if you miss the connection, tough. It's your problem.

The other rip off this allows, is a hefty whack on your bill. The cost of A to B and the cost of B to C (which you now have to pay) is not the same as the cost from A to C via B, (which you were able to pay). I have seen this "virtual" scrapping of interlining cost people up to 50% more than the through ticket cost.

To make matters worse some airlines (eg British Midland) now say that they will not check people through on interline etickets as the cost of doing this is to high. Err, yes. Any excuse will do. 

There are two answers to this problem. Firstly, if your flights involve en route changes across airlines, always get a paper ticket not an eticket. Even if you have to pay £25 or so, it will make your life easier. Secondly, if you can only get an eticket, make sure the second flight is with an airline that has online checkin. You can then checkin for your second leg before you start your first. When you go to checkin at the start of the journey you are then able to present a boarding pass for the second leg of your journey and any check in person would be hard pushed to find an excuse not to check you through. Once checked through and you miss your connection, you will still have a bit of ranting to do but airline two and one will be hard pushed to find a reason not to admit defeat. (Sorry about the number of "checkin" words and their variations) Be warned, though. With some airline online checkin systems, you only get one shot at printing a boarding pass (eg BA) so make sure your printer is online and there is paper in it etc., etc., FIRST!

Mind you, you will still have a problem if a low cost carrier gets its nose into your itinerary. These outfits never mixed ("interlined") with anyone so you will always be on a wing and a prayer with regard to connections. Better off to stick with the full service boys, even if it costs more money. It is, in my opinion, fair enough for the genuine low cost types like RyanAir and Easyjet - the airlines that do exactly what they say on the tin, nothing more, nothing less but pathetic when it comes to those that want to keep a foot in both camps, such as lost-the-plot airlines (aka Aer Lingus) or indeed the (normally) mild mannered British Midland with their banal BMI baby offshoot.

Have fun!