Shares of airlines aren't having a good summer.

Since July 7, when it reached an all-time high, the Standard and Poor's Composite Airlines Index has fallen 17%. Of the eight major airlines, only Southwest Airlines Co. (LUV) has a year-to-date share price gain with its shares are up 5%.

The industry may get a chance to explain itself and perhaps reduce guidance this week. Key events include Delta Air Lines Co.'s (DAL) August traffic report, scheduled for Tuesday, Sept. 5; and the Cowen & Co. airline investor conference on Wednesday, Sept. 6.

With United Continental Holdings Inc.'s  (UAL)  chief financial officer in the spotlight after Hurricane Harvey struck Houston, the carrier's second-biggest hub, CFO Andrew Levy is scheduled to speak at the conference at 8:30 a.m. ET.

Cowen & Co. analyst Helane Becker wrote last Wednesday that she expects "managements will update guidance to the low end of the range" at the conference.

"Pricing trends are currently not favorable," Becker wrote. "Fares from the Northeast to Florida are again in double digits [and] walk-up fares in some markets are lower than advance purchase fares."

In particular, Becker said, walk-up fares in Denver, Newark and Chicago, are lower than expected. All three cities are United hubs where ultra-low-fare carriers have impacted pricing.

"If this continues into the December quarter, estimates will require another round of revisions," she said.

UBS analyst Darryl Genovesi also takes a dim view of industry prospects following an industry conference in Las Vegas last week.

"Domestic revenue trends have taken another leg down since initial Q3 guidance," Genovesi wrote in a recent report. He said most carriers may cut current third-quarter guidance.

Factors in the decline include efforts by United, American Airlines Group Inc. (AAL) and Southwest to match fare reductions by ultra-low-cost carriers Spirit Airlines Inc. (SAVE) and Frontier Airlines, geopolitical events and the impact of Hurricane Harvey, he said.

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