Major U.S. airlines collectively doubled their net profit in the first six months of the year compared to the same period in 2014, according to Airlines for America (A4A). Recovering from the recession of 2008-2009, U.S. airline profitability approximates that of other large corporations, allowing carriers to invest in new aircraft, services and technology at the highest rate in 15 years, the trade group said on August 18.

The 10 publicly traded carriers A4A tracks combined reported $8.7 billion in net profit in the first half of the year, up from $3.9 billion during the same period last year. This translates to a net margin of 11.2 percent, or about 11 cents on every dollar of revenue, which exceeds the S&P 500 index of 8.9 percent, the trade group said. The closest comparison is the Chipotle restaurant chain at 11.5 percent net profit margin, according to its calculations.

At the same time, total operating revenues of $78.2 billion were essentially flat, inching up 0.4 percent year over year. But a 34-percent decrease in fuel expenses helped drive profitability.

“Deep into this business cycle, six years post-recession, U.S. airlines at last are achieving profitability that is in line with the average U.S. company,” A4A chief economist John Heimlich said in a conference call. The margins have allowed them to hire more workers, raise wages, acquire 367 new aircraft and increase capacity on domestic routes to its highest point since 2009, he added.

Airlines increased their domestic capacity by an average of 5.5 percent in terms of year-over-year domestic available seat miles. Low-fare carrier Spirit Airlines led all other carriers, growing its capacity by 35 percent. United Airlines showed the least growth in available seat miles. Other carriers falling below the average growth rate were Virgin, American, Delta and Hawaiian.

On July 1, the U.S. Justice Department said it was investigating “possible unlawful coordination” by some airlines to keep prices high by limiting capacity, according to media reports. A4A has said the allegation is unfounded. Fares overall fell by 1.9 percent during the first half of the year, it reported.