United Improving 757 Capacity with Slimline Seats

United Airlines will be fitting its Boeing 757-300 fleet with slimline seats by the middle of 2018, increasing the number of economy seats on the aircraft to more than 200.

The Chicago-based carrier will add 21 seats to the main cabin on the aircraft for a total of 210 seats. First class will continue to have 24 seats.

United's reconfigured 757-300s will have 234 seats, up from 213 currently. Delta Air Lines, the only other US carrier flying the aircraft, also configures its 757-300s with 234 seats.

The 757-300 is the latest aircraft in United's fleet to receive additional economy seats. The carrier is reconfiguring its legacy United Boeing 767-300ERs with 214 seats from 213 as it installs its new business class.

United began installing slimline seats on narrowbody mainline aircraft in 2012, beginning with its Airbus A320 family fleet. It now has them on most of its A319s, A320s and Boeing 737s.

Almost all US airlines are in the process of adding, or have added, seats to certain aircraft models in their fleets. Adding seats to an aircraft in a carrier's fleet is a cheaper way to increase passenger capacity and reduce unit costs, rather than purchasing new or additional aircraft.