United Airlines said Tuesday it had ordered 50 Airbus A321XLR aircraft, worth an estimated $6.5 billion, to replace an existing fleet of aging Boeings.

The new Airbus planes, to be delivered starting 2024, will allow United to retire its Boeing 757-200s, the company said.

The Airbus order is the latest blow to the American manufacturer, already deeply mired in the crisis surrounding its 737 MAX, which has been grounded worldwide after two crashes that resulted in 346 deaths.

Boeing has no new aircraft to compete with the Airbus A321XLR in the mid-market range.

Airbus launched the A321XLR only this year, at the Paris Air Show in June.

The single-aisle aircraft's range is 15 percent above that of its predecessor, the A321LR, making it a cost-effective alternative to long-haul wide-body planes.

It's larger fuel tanks allow it to cover up to 5,400 miles (8,700 kilometers) in nine hours -- significantly more than the Boeing 737 MAX.

United said it intends to use the new aircraft to serve additional European destinations from US East Coast hubs in Newark/New York and Washington.

The airline turned to Airbus for the purchase because Boeing does not have an aircraft in the mid-market range, a source close to the matter told AFP on condition of anonymity.

United Airlines, whose fleet mainly consists of Boeing planes (similar to the 737 MAX planes pictured), placed an order for 50 Airbus A321XLR aircraft
United Airlines, whose fleet mainly consists of Boeing planes (similar to the 737 MAX planes pictured), placed an order for 50 Airbus A321XLR aircraft GETTY IMAGES NORTH AMERICA / JUSTIN SULLIVAN

"There are no aircraft currently offered by Boeing that can replace the 757," the source said, adding that negotiations between Airbus and United began several months ago.

Boeing, which is currently focused on returning its MAX aircraft to the sky, has already postponed until next year the possible announcement of a new model aircraft (NMA) intended to replace the 757 and 767.

The manufacturer recently presented the design to various airlines, including United, industrial sources told AFP.

Boeing still aims to have the NMA enter service in 2025, the sources said.

"We will take a close look at this aircraft," said Andrew Nocella, United chief commercial officer, during a call with reporters.

He added that United has not ruled out the possibility of buying the NMA should Boeing build it.

United's international fleet is made up mainly of Boeing models: the 757, 767, 777 and 787 Dreamliner. The airline also has 14 737 MAX planes, which are currently grounded.

When contacted by AFP for comment, Boeing -- which now lags Airbus in terms of both orders and deliveries -- did not respond immediately.

Airbus decided to no longer publish the catalog prices for its aircraft beginning in 2019. However, the A321XLR is a long-range version of the A321, whose unit value was $129.5 million in 2018.

United has meanwhile postponed receipt of its first 45 Airbus A350 long-haul aircraft by five years.

The company, which ordered the planes in 2017, said it now plans to have them delivered in 2027 instead of 2022.