GENEVA, Sept. 14 (Xinhua) -- The latest data of the second quarter this year reaffirmed a decline in airline profitability, compared to the same quarter a year ago, the International Air Transport Association (IATA) said Friday.

It said in its Airline Financial Monitor that industry-wide cash flow generation was broadly unchanged compared to the second quarter in 2017.

"Global airline share prices edged higher in August, matching the wider global equity index, and consolidating the strong gain recorded in July," said IATA.

August's improvement in the airline share price index was driven solely by the North American carriers.

Airline shares are still 10 percent lower than at the beginning of this year, said IATA.

Oil prices eased slightly again in August, but IATA said the upward trend remains in place. Jet fuel prices were steady, at just under 90 U.S. dollars a barrel.

IATA said passenger yields continue to trend lower overall, however, as premium cabin yields continue to show more resilience than that of the economy cabin, helping to offset some of the impact of higher input prices.

Passenger demand remained robust at the start of the peak northern hemisphere summer period, growing at an above-trend rate.

Freight demand has slowed over the recent period, slipping below the pace of capacity growth.

"In terms of revenue, premium-class passengers accounted for 31 percent of passenger revenues over the first half of 2018. Again this figure was unchanged from the same period a year ago," said IATA.

Higher passenger loads continue to support airline financial performance despite the ongoing softness in passenger yields.

IATA said, however, the converse holds for the freight segment where capacity is outpacing demand.