Updated from 1:13 p.m. ET

Southwest Airlines Co. (LUV - Get Report) disappointed investors Thursday as it guided toward lower-than-expected current quarter unit revenue on the same day as commentary from Spirit Airlines Inc.'s  (SAVE - Get Report) earnings call dragged airline shares lower.

Southwest shares traded down nearly 5%, while shares in Spirit were down 18%. All of the major airlines were showing share price declines, with most declines in the range of 1% to 2%.

Southwest said it expects current quarter revenue per available seat mile growth to be approximately 1% "which includes an estimated year-over-year unfavorable impact from the transition to the new reservation system of approximately 1 point."

The carrier said it doesn't expect the impact to continue beyond the current quarter.

In the second quarter, Southwest RASM grew 1.5%. The carrier said growth would have been higher, but the figure "included less than 1 point of temporary pressure attributable to the transition to the new reservation system. "

Speaking on CNBC, Southwest CEO Gary Kelly said the quarter "was right in line with our expectations." Kelly called the introduction of new reservations systems "flawless" but also said results included "some drag" from that new system that will get remedied shortly. For instance, he said, the introduction of a new boarding product "is a little bit more complicated to sell than our previous system."

Southwest reported earnings per share of $1.24, ahead of the consensus estimate of $1.20. Revenue rose 6.7% to $5.7 billion. The 1.5%-unit revenue gain was in line with expectations. Cost per available seat mile grew 5.3%, generally in line with expectations.

JPMorgan analyst Jamie Baker said the combination of Southwest's guidance indicates that the consensus current quarter earnings estimate of $1.10 may be too high: it should be about 95 cents a share, he said.

Even before the Spirit earnings call, Baker said the outlook for the airline sector has dimmed.

"Southwest's uninspiring RASM guide and anticipated decline in consensus forecasts offers little, if anything, in terms of potentially arresting the sector's current correction, he said. At this point, most names are off 5% to 8% from the start of earnings season (worse for UAL), despite a 1.5% rise in the S&P."

However, CFRA Research analyst Jim Corridore said he raised his target price for Southwest to $70 from $64.

Corridore said his price target comes with a price earnings ratio of 14.5 times his 2018 estimate of $4.82, but he noted that is "well below the S&P 500.

"We think LUV and airlines in general are likely to see valuation expansion on steady profits and return on invested capital," Corridore wrote.

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This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.