Depends on how long your longhaul flight will be! And what insulin regime you are on. I fly to the US 5-6 times a year, and occasionally much further. Historically I always found that it was my long-acting insulin that needed tweaking, adjusting the dose according to how many hours I was losing or gaining. Short-acting was always dependent on the food I was eating so no major changes there. Still use the same principles with my pump.
Don't forget to take all your diabetes paraphernalia with you in the cabin, you'll certainly be testing and probably more so than usual. So it's not a bad idea to have a letter from your GP/consultant just in case you are questioned about lancets, needles etc at security. I never have been, but there's always a first time...
Talking of security, some airports are still a bit twitchy about taking liquids on board. I've always found the best hypo treatments to be in liquid form, so to get around this quandary buy a few cartons of emergency fruit juice AFTER passing through the security check. No problem at all.
And have a great trip! :wink: