The U.S. Treasury Department said on Saturday it has released US$9.5 billion in additional funds from the Payroll Support Program to U.S. air carriers, bringing to US$12.4 billion the total provided to the airline sector hit hard by the coronavirus pandemic.

In total, the government has disbursed grant funds to 10 major airlines and 83 smaller carriers.

Congress approved US$25 billion in grants for payroll assistance for passenger airlines. Treasury required major airlines receiving more than US$100 million in assistance to repay 30% in low-interest loans over 10 years and issue warrants equal to 10% of the loan amount.

Airlines must not cut pay or jobs through Sept. 30 as a condition of the grants and are barred from buying back stock or paying dividends and face restrictions on executive compensation.

SkyWest Inc Chief Executive Chip Childs told employees on Friday the airline expects to receive US$438 million from Treasury in payroll assistance.

"There is still much about the future and recovery that remains uncertain, and there is a very real possibility that we could be a smaller airline by the end of the year," he wrote in a email seen by Reuters.

The four largest U.S. carriers are receiving US$19.2 billion in total out of the US$25 billion - American Airlines Group Inc, Delta Air Lines Inc, United Airlines Holdings Inc and Southwest Airlines Co.

Treasury is awarding major carriers 50% of the grant funds initially and then releasing the remainder through July.

Treasury said additional money will continue to be provided to approved applicants "on a rolling basis."

The department is still reviewing how to award US$4 billion in grants to cargo carriers and US$3 billion to airport contractors such as caterers.

Cargo carriers that receive US$50 million or less of payroll support and contractors that receive US$37.5 million or less "will not be required to provide financial instruments as appropriate compensation" for support, the department said.

The Treasury Department also published on Saturday the application form for companies deemed critical to maintaining national security seeking loans from a US$17 billion fund.

The fund has been mentioned as a potential source of funds for Boeing Co (BA.N), which declined to say on Friday whether it would apply. Treasury said it wants companies to apply by May 1.

Treasury has an additional US$25 billion in loans it can award to passenger airlines and US$4 billion in cargo loans. Some airlines, including American, Delta and Alaska Airlines, have already applied.

Airlines may still need more money as U.S. air travel demand has fallen by 95% and shows no sign of improving.

On Friday, President Donald Trump said the U.S. government could pre-buy airplane tickets at a steep discount of 50% or more for travel for the next four or five years. "You infuse them with some cash. And in the meantime, we're flying the people of our country for ... a fraction of the cost," he said.

Airlines for America, a trade group representing major U.S. airlines, declined to comment.