Delta Air Lines (NYSE:DAL) lost $2.1 billion in the fourth quarter and $15.6 billion for the year as the pandemic took its toll on the airline sector, but the company said it is optimistic the worst is behind it heading into 2021.

Early Thursday, the airline reported a fourth-quarter adjusted loss of $2.53 per share on revenue of $3.5 billion, falling just short of analyst consensus estimates for a $2.51 loss per share on revenue of $3.6 billion. Delta bled through about $12 million per day in December, a 90% reduction from the airline's burn rate back in late March at the beginning of the pandemic.

A Delta 777 from the front.

Image source: Delta Air Lines.

For the year, Delta posted a pre-tax loss of $15.6 billion on revenue of $17.1 billion, a remarkable negative 91% margin.

"Our December quarter results capped the toughest year in Delta's history," CEO Ed Bastian said in a statement announcing the results. "While our challenges continue in 2021, I am optimistic this will be a year of recovery and a turning point that results in an even stronger Delta returning to revenue growth, profitability and free cash generation."

Airlines hope that as the COVID vaccine becomes more widespread, travel will return, but it will be a slow, gradual process. Delta expects first-quarter 2021 revenue to fall by 60% to 65% from a year ago, with scheduled flight capacity set to shrink by 35%.

The results, though bad, demonstrate Delta's ability to weather the storm.

The airline expects average daily cash burn between $10 million and $15 million in the quarter. Delta ended the year with $16.7 billion in total liquidity, and assuming U.S. Treasury payroll support funds come in as planned, the airline hopes to end the March quarter with $18 billion to $19 billion in liquidity.

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