United Airlines expects to introduce its new premium-economy cabin on a Boeing 777-200 by the beginning of July, as it begins retrofitting its widebody fleet with the product.

The aircraft will enter service with 24 Premium Plus seats in a two-four-two configuration, as well as the Chicago-based carrier's Polaris business class product, in "late June", United said in a flight attendant newsletter on 13 June. It does not say which routes the aircraft will operate.

United joins its long-haul peers, which all offer a premium economy product, with Premium Plus. The cabin features wider seats with more recline than economy, as well as a dedicated onboard service.

The airline will initially sell and cater Premium Plus as an extra-legroom economy seats, and plans to begin selling it as a dedicated class in the fourth quarter or early 2019, United chief commercial officer Andrew Nocella said in April. The dedicated onboard service will begin in early 2019.

"[Premium Plus] further pushes us down the road as segmentation, particularly with the mid-tier cabin," he said at the time. "We're really confident in its ability to deliver value for the airline."

United is targeting $1 billion in additional revenue from segmentation, which includes no-frills basic economy fares as well as the new premium-economy cabin, by 2020.

US carriers have long held off on introducing premium economy, instead offering passengers a buy-up to extra-legroom economy seats. American Airlines was the first to offer a dedicated premium-economy product in 2016, followed by Delta Air Lines in 2017.

United initially plans to install Premium Plus on its 767-300ERs, 777-200s and -300ERs, and 787-10s, it said in an employee update earlier this year. It will install 22 of the seats on the 767s, 24 on the 777s and 21 seats on the 787.

The carrier will continue to offer its extra-legroom economy-plus product on board these aircraft.

The second aircraft in United's fleet with premium economy seats will be the 777-300ER, the airline says in the newsletter.

United operates 35 767-300ERs, 74 777-200s and 17 777-300ERs, Flight Fleets Analyzer shows. It has one additional 777-300ER and 14 787-10s on firm order.

Source: Cirium Dashboard