United Airlines has struck a deal with an Asian aircraft leasing firm to sell and then lease back 22 aircraft. Neither United nor the Bank of China Aviation revealed the financial terms of the deal announced Sunday morning.

The move will help United conserve cash and give its balance sheet greater flexibility as it faces mounting losses due to coronavirus causing a global plunge in airline travel.

Earlier this week, United CEO Oscar Munoz said business has essentially dropped to zero. "We expect to fly fewer people during the entire month of May than we did on a single day in May 2019," Munoz wrote in a note to employees outlining plans to cut its schedule by 90% in May.

The letter and warning came one day after the airline agreed to a $4.9 billion payroll grant from the U.S. Treasury.

Sixteen of the planes involved in the deal are 737-9 Max models that have not yet been delivered by Boeing. United currently has approximately 800 planes in its fleet.

Sale-leaseback agreements offer airlines greater financial flexibility while ensuring they will have the planes needed to fit their schedule. For aircraft leasing companies, sale-leaseback agreements typically allow them to expand their portfolios while buying planes at a discount.

Cirium, an aviation consulting firm, says airlines have parked more than two-thirds of the commercial airplanes in the world. Given the extremely weak outlook for domestic and international travel, many analysts have predicted the industry is entering a period where carriers will defer or cancel orders.

Another possibility is for airlines to sell their planes to other airlines or aircraft leasing firms.