The I.A.T.A. proposal aims at a real problem. Carry-on bags have gotten bigger at the same time that planes have gotten more full: On average, commercial flights on American carriers rose from 73 percent full in 2002 to 83 percent full in 2014. Those trends, and the imposition of fees for checked baggage, have combined to mean overhead bin space is increasingly scarce, and airlines must more frequently gate-check carry-on bags, which delays boarding and annoys passengers.
The association says nine non-U.S. carriers, including the German airline Lufthansa, have "confirmed interest" in offering some sort of preference to the Cabin OK bags. Lufthansa is "currently evaluating" the proposal, according to a spokeswoman, Christina Semmel.
But no airline seems to be adopting the new size as an absolute limit, and United States carriers show underwhelming enthusiasm for adopting Cabin OK preferences. United said it is studying the proposal. But representatives for Delta, American, Southwest and Alaska said they had no plans to change their carry-on size limits.
"We are comfortable with our size requirements," said Bobbie Egan, a spokeswoman for Alaska Airlines, which already offers a slightly more generous than normal carry-on allowance.
Instead of pushing smaller bags, Alaska is taking an approach to accommodating carry-ons that befits America's largest state: bigger bins. The airline says overhead bins on its new Boeing 737-900 aircraft are 48 percent larger than its old bins, and deep enough for typical rollaboard suitcases to be loaded in on their sides. Delta also cited larger overhead bins, which it's putting on some domestic and international aircraft, as its focus for improving the "carry-on experience."
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It's not surprising airlines would be reluctant to introduce a rule to promote smaller carry-ons, given the way they treat the rules they already have in place.
"In the past, U.S. airlines have not enforced their existing carry-on luggage standards, so American consumers continued to purchase the larger sized carry-ons," said Stephanie Goldman, a senior director for marketing at the luggage manufacturer Samsonite.
She's right. Go get a tape measure and check the dimensions of your rollaboard suitcase. You might find, as I did, that it's 15 inches wide — an inch too wide to go on a plane, even though I've actually taken it on board hundreds of times across many different airlines. United even sells a "carry-on" suitcase through its MileagePlus store that is, technically, an inch too deep and 2.25 inches too wide to carry on a United plane.
Airlines have reasons not to be sticklers about carry-on baggage. Tight enforcement means testy, time-consuming exchanges with staff as passengers squeeze and shove to show that, if you try hard enough, their suitcases do fit into a size-wise bin. Additionally, by letting their most frequent fliers board first, airlines ensure their most valuable customers get access to bin space, even on flights where there isn't enough room for everyone's bags.
The Cabin OK initiative could make bag enforcement even more complicated: If there is a maximum luggage size and a separate, smaller "optimum" luggage size, and maximum bags are allowed on some flights but only the optimum bags are allowed on the most full flights, customers will find it even harder to understand the rules and might get even more annoyed when they're separated from their bags.
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In practice, enforcement goes in cycles, says Gary Leff, who writes the View from the Wing blog on frequent-flier programs.
"For instance, in February-March 2014, United was making a concerted effort to enforce carry-on sizes," he wrote in an email. "When it's a company priority, gate agents do it. Time passes and it doesn't get management attention, then things become more lax. Then it becomes gate agent-specific. Some gate agents take it upon themselves to enforce rules, to 'go by the book,' while most do not. That seems to be true across airlines."
If the airlines change their approach and start tightening the rules, the luggage makers will be there for you.
"We already offer products that meet the proposed standard, and will be prepared to expand such offerings should the proposed standard become widely adopted," said Ms. Goldman of Samsonite. A spokesman for Travelpro said the company already had a Cabin OK-compliant suitcase in development.
But for now, you are free to continue stuffing your enormous rollaboard bag into a bin where it barely fits.