Delta Air Lines Inc. concluded the "toughest year" in its history with a larger-than-expected loss in the fourth quarter of 2020, although the company remains optimistic for a recovery in 2021 despite the lingering impact of the coronavirus pandemic.

The airline booked an adjusted net loss of $1.60 billion, or $2.53 per share, in the fourth quarter, compared with a net income of $1.10 billion, or $1.70 per share, in the year-ago period. The S&P Capital IQ consensus normalized loss per share estimate for the fourth quarter was $2.45.

For the full year, Delta reported an adjusted net loss of $6.84 billion, or $10.76 per share, compared with a 2019 adjusted net income of $4.78 billion, or $7.32 per share.

Delta's adjusted operating revenue plummeted 66% to $15.95 billion in 2020 from $46.72 billion in 2019. In the fourth quarter, adjusted operating revenue fell 69% year over year to $3.53 billion from $11.39 billion.

"Our December quarter results capped the toughest year in Delta's history," Delta CEO Ed Bastian said. "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."

Delta, which ended 2020 with $16.7 billion in liquidity, reduced its average daily cash burn to $12 million in the fourth quarter from $24 million in the previous quarter.

Delta President Glen Hauenstein expects the recovery in 2021 to come in three phases, with the first one characterized by "choppy demand recovery and a booking curve that remains compressed."

The next stage will be an "inflection point," Hauenstein said, followed by a sustained recovery in demand "as customer confidence gains momentum, vaccinations become widespread and offices reopen."