Travelers, Welcome to the Revolution in Overhead Bin Size

American Airlines, which now has big bins on two-thirds of its single-aisle airplanes and will get to 75% probably in April, says customer satisfaction scores are 5 percentage points higher on Boeing 737s with “Space Bins’’ than on 737s with conventional smaller bins. On the Airbus A321, surveys show customer satisfaction is 8 percentage points higher with Airbus XL bins than without, according to Alison Taylor, American’s chief customer officer.

“People are a bit anxious about getting your luggage in,’’ Ms. Taylor says. With big bins, “it’s quicker to get your luggage in and also to get your luggage out…It’s actually played out even better than we thought.’’

Airlines say they see fewer delays from gate-checking bags right at departure time. Flight attendants and gate agents appreciate not having to carry bags to the front of the plane and tag them at the last minute, or waiting for passengers to stubbornly try to smash bags into already-full bins.

Alaska has Space Bins on 56% of its Boeing fleet. That number will grow as new deliveries come online.

“This was a tangible guest improvement,’’ says Sangita Woerner, Alaska’s senior vice president of marketing and guest experience. “I think it was a game-changer when we launched it in terms of making it more seamless to board, the stress on the guests, the stress on the gate agents and flight attendants.’’

In air travel, tangible improvements are often few and far between. Fast Wi-Fi is appreciated by travelers. Extra legroom, too. Having enough overhead bin space for all passengers might seem as if it should be standard, but turns out to be rare.

Space in overhead bins is so prized that people stay loyal to an airline just for early boarding status, which doesn’t get you much except for available bin space. Some passengers pay extra for early boarding just to avoid having to check a bag. Woe be the passenger who has to endure the walk of shame back to the front of the packed plane and have his or her carry-on bag checked.

For years airlines were selling ticket-holders false hope. Everyone gets to bring one carry-on bag and one personal item such as a purse or backpack. But the truth was if everyone brought their full allocation, there wasn’t enough bin space.

That simple math got a lot worse for passengers when airlines crammed more seats into their jets, reducing legroom and pushing heads closer together with thin webbing in seat backs instead of thick foam. American went from 148 seats on a Boeing 737-800 to 160 and now 172. The bins didn’t get any bigger, so more passengers were competing for the same overhead bin space.

It got even worse when most airlines started charging fees to check bags in 2008 and passengers responded by loading up free carry-ons.

Alaska asked Boeing to come up with a solution. Engineers at Boeing had already been working on ideas to reroute wiring and pipes in the ceiling and create more bin space. The taller Space Bins sit 2 inches lower, reducing some headroom, and pivot up and away from the aisle as they are pushed up into the ceiling.

A standard 60-inch bin can carry four bags laid flat, Boeing says. The 60-inch Space Bin can carry six turned on their side. The most common 737, the 737-800 and its newer same-size version, the 737 MAX 8, has room for 118 bags in standard configuration, Boeing says. With Space Bins, the 737 MAX 8 can carry 178 bags—enough for the 172 passengers American packs in.

Alaska flies 79 Boeing 737-900ERs with Space Bins and 178 seats. That aircraft went from 134 bags in standard overhead bins to 199 with Space Bins.

Boeing says about half of all MAX deliveries have the bigger bins installed. It is an option for airlines—and some still don’t want them. Southwest, for example, is sticking with standard bins because it offers two free checked bags and doesn’t want pack rats in the cabin.

United is onboard. The airline announced orders in June for 200 Boeing 737 MAX and 70 Airbus A321neos, and made a point of saying all would be delivered with large bins.

Bin space is much more of an issue on single-aisle airplanes, known in the business as “narrow-bodies.’’ Wide-body jets, with two aisles, usually have ample bin space.

It has taken some education for fliers. Big bins typically have stickers instructing passengers to load bags wheels first and turn them on their side rather than laying them flat. American’s flight attendants make announcements during boarding about the bins, including in Spanish for international destinations in the Americas.

American says its high percentage of narrow-body jets with big bins has helped it win corporate accounts or move to higher preferred status, or first choice, at companies rather than just being one of several airlines in a corporate travel discount program.

Ms. Taylor says she recently visited four good-sized corporate customers in Seattle with Alaska, American’s partner, and two of the four travel directors mentioned big bins as a reason for sticking with American.

“We know for a fact that we’ve gone from being non-preferred to preferred at a nice corporate account in the last two months because we have 66% [of narrow-body fleet with big bins],’’ she says. “It is that important to travelers.’’

Write to Scott McCartney at middleseat@wsj.com