I am looking to purchase a piece of carry-on luggage for my trip from the US to the UK on Lufthansa, from the UK to Turkey on Turkish Airlines, and from Turkey to the USA on Air Canada. The carry-on luggage will be used to transport cameras, electronics...that i do not want to pack in my check-in luggage. Most of the the carry-one luggage that are for sale are 22 x 14 x 9 inches which is acceptable to most airlines. However, Turkish Airlines places a length limit of 21.8 inches or 21 and 21;/32 inches depending upon the source of information. Will they really quibble over 1/3rd or 1/8th of an inch? I am not sure of the luggage that I am targeting, Osprey Porter 46 or Eagle Creek Digi Hauler, have compression straps that allow one to shorten the length.
I also noticed that they're a little outside the norm as we're flying next month. In October 2012, my husband and I both carried on the Osprey Porter 46 (either not noticing the size issue or they've changed their requirements since) and didn't have any problems on any of the six Turkish Airlines flights we took. Should be interesting to see if we have issues this time.
If I have any problems I will post the experience. However, I have purchased two web straps off of ebay for $1.50 apiece in order to compress the luggage by maybe 1/2 inch and satisfy the airline. It appears that most airlines allow lengths of 56 cm or 22 inches while Turkish Airlines and Lufthansa, among others, only allow 55 cm.
I just returned from Turkey and had four flights with Turkish Airlines - three one-hour flights within Turkey and our 10-hour flight home to Toronto. We were concerned about the carry-on size, but saw lots of people with larger than average carry-on wheeled suitcases and the flight attendants just made them fit. I never saw anyone working for the airlines measure much less look at the carry-on bags. Just be polite and confident and I'm sure you won't have a problem.