The deal, which United Airlines called the "biggest widebody order by a U.S. carrier in commercial aviation history," was announced on Tuesday and calls for the purchase of up to 200 additional widebody aircraft.

The airline announced that it had placed a 100-aircraft Boeing 787 Dreamliner order, with 100 more options. According to United, it will select a mix of the 787-8, -9, and -10 models when each one enters production for the aircraft. Presently, each variation is used by the airline.

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The purchase comes over a year and a half after United placed orders with Boeing and Airbus for a total of 270 narrowbody aircraft, claiming that it was the single-largest order in company history at the time.

Since the airline's fleet of Boeing 767s and some of its 777 widebodies is ageing, there have been rumours of an upcoming order from United for some months. According to the airline, the 767 fleets will be replaced by the new Dreamliners, with a full retirement date of 2030 for 767 fleets.

In a media conference on Monday evening in advance of the announcement, chief financial officer Gerry Laderman described the order as wholly focused towards replacing the deteriorating widebody fleet. United will take receipt of the new aircraft from 2024 through 2032.

We will have around 12 widebody 767 and 777 aeroplanes that are 30 years old within that same 10-year period, according to Laderman. "Now is the time to consider retiring those planes. The 767 and a few 777s will so be replaced by these 100 firms [aircraft orders]."

According to chief commercial officer Andrew Nocella, the flexibility of the alternatives means United might expand its global reach as the market permits. The new possibilities enable "opportunity" based expansion in the future, according to Laderman.

If these alternatives are taken, he predicted that by 2030, the 787 platforms would account for more than 80% of all of his company's long-distance flights. "It improves our dependability, simplifies operations, and provides a pleasant flying experience for our passengers."

What this would mean for United's long-standing contract with Airbus for the widebody A350, a direct rival to the 787, was not immediately obvious. Currently, United is ordering 45 A350-900 twinjets, which were converted from an initial 2010 deal for 35 larger A350-1000 aircraft in 2017.

At the moment, United has delayed fulfilling that order until 2030, according to Laderman, and will decide on the next line of action when the time comes.

As a 777 replacement, he remarked, "the A350 is a pretty great alternative." We'll make a choice later, but we're aware that not all of the 777s are being replaced in this order.

Notably, Laderman said, adding the 350s would complicate United's plans for hiring and training pilots, add another layer of complexity to its long-haul fleet, and increase its costs.

"As a 787 operator, we already exist. When you are currently the owner of a modern, effective aircraft, it makes little economic sense to add another fleet type."

With Polaris business class, Premium Plus premium economy, and coach with extra-wide seats, United intends to set up the new 787s in a similar three-cabin layout as its existing aircraft. According to Nocella, there are no intentions at this time to replace the business class product with a new seat design, but this could change before the current order is entirely fulfilled.

We'll keep installing it because we believe it's a fantastic seat and our clients do too, he added. The decision will be made because this delivery stream will last for ten years. However, for the time being, an identical seat will be installed.

The airline also increased the number of 737 MAX aircraft it has on order with Boeing, exercising options for 44 further 737 MAX aircraft between 2024 and 2026 and putting 56 additional orders for MAX versions to be delivered between 2026 and 2028. According to the airline's news release, United has nearly 700 new planes on order for delivery between now and 2032. The company anticipates an average delivery rate of more than two per week in 2019 and three per week in 2024.

In addition, United gave an update on its cabin conversion effort, saying that it anticipates completing the installation of its present Polaris and Premium Plus seats on all international widebodies by summer – more than 90% of that fleet is already complete. A new cabin, which is now being supplied on certain new aircraft, will be retrofitted onto the whole mainline fleet by the end of 2025, the company added. Despite what some observers have noted as the narrow-body refit program's sluggish start, the airline stated that 100 aircraft are expected to have new interiors in 2023.