Full-year passenger traffic is set to decline 66%, the International Air Transport Association (IATA) said, compared with a previously forecast 63% decline.
"The improvement that we saw in the summer months has more or less stopped," IATA Chief Economist Brian Pearce said.
August traffic was down 75.3% in terms that reflect passenger numbers as well as distance flown, compared with a 79.5% drop in July.
Airlines are pressing governments to abandon quarantines and other travel curbs blamed for worsening the slump, and instead roll-out rapid Covid-19 testing at airports.
Load factors that measure the proportion of aircraft seats filled fell 27.2 points to a record low of 58.5% in August.
"The industry is restarting but it looks as though it's still burning through cash," Pearce said. Losses will continue to mount throughout 2020, with bookings data pointing to a weak fourth quarter.
August's short-lived improvement was driven by domestic routes, down more most 50% year-on-year, while international traffic was 88% lower.
A rebound in Russia's domestic market, up 3% on last year, contrasts with Australian flights still down 88% and Chinese internal traffic still 19% lower year-on-year, IATA said.
Cargo demand was down 12.6% in August, an improvement on July's 14.4% decline, it also said. The grounding of passenger jets has reduced capacity, supporting prices.
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