Passengers on US planes are finding themselves in a tighter squeeze as airlines install new slimline seats that take up less space from front to back, allowing for five or six more seats on each plane.
The changes, covering some of the most common planes flown on domestic and international routes, give the airlines more paying passengers and a smaller fuel bill because the seats are slightly lighter.
Some passengers seem to mind the tighter squeeze more than others. The new seats generally have thinner padding. And new layouts on some planes have made the aisles slightly narrower.
Whether the new seats are really closer together depends on how they are measured. By the usual standard, called "pitch," the new ones are generally an inch closer together from front to back as measured at the armrest.
Airlines say passengers will not notice. The seats going onto Southwest's 737s have thinner back magazine pockets. Alaska Airlines will have slightly smaller tray tables. United's new seats put the magazine pocket above the tray table, getting it away from passengers' knees. And seat-makers saved some space with lighter-weight frames and padding.
This allows airlines to claim that passengers have as much above-the-knee "personal space" as they did before, even if the seats are slightly closer together below the knee.
New seats going into United Airlines' Airbus A320s are an inch closer from front to back. The new seats Southwest has put on nearly its entire fleet are 31 inches apart, about an inch less than before. In both cases, the airlines were able to add an extra row of six seats to each plane.
International passengers are feeling crowded, too. As recently as 2010, most airlines buying Boeing's big 777 opted for nine seats across. Now it is 10 across on 70% of newly-built 777s, Boeing says.
The extra seat has generally meant narrower aisles, and more knocks from the drinks trolley for those at the end of the row which is the biggest complaint from travellers according to Mark Koschwitz of SeatExpert.com.
"We used to recommend the aisle seats, because you could stretch out more," he said. He now tells passengers who want to sleep "to bring a jacket and prop up against the window."