A U.S. airline stock index fell for the eighth straight day, its longest slide in two years, after United Continental Holdings Inc. posted a quarterly profit that missed analysts’ estimates.

United dropped 5.9 percent to $19.20 at the close in New York to pace a 0.8 percent decline in the Bloomberg U.S. Airlines Index. United’s earnings excluding some items were $1.41 a share, trailing the $1.66 average estimate of 17 analysts surveyed by Bloomberg.

Fuel costs rose and a computer change damped sales, Chicago-based United said. Revenue of $9.94 billion was less than analysts’ $10.1 billion estimate as the world’s largest carrier combined accounting systems under the 2010 merger of former United parent UAL Corp. and Continental Airlines Inc.

“It is poor execution that, unfortunately, continues,” said Hunter Keay, a Wolfe Trahan & Co. analyst in New York who rates the shares as outperform.

United has moved to reverse a slide in on-time arrivals and an increase in lost bags and canceled flights, Chief Executive Officer Jeff Smisek said. The company is rebuilding its reserve of spare jets at the United Airlines unit to 15, after stumbling when it cut back to nine in adopting a preventive maintenance program used by its Continental operations.

‘I Apologize’

“I know we caused some customer disturbance because of all the changes we implemented so quickly, and I apologize for that,” Smisek said on a conference call with analysts.

Profit excluding some items fell to $545 million from $577 million, or $1.49 a share, a year earlier, United said in a statement. Including $137 million in costs to repaint planes and make other merger-related changes, $76 million in severance expenses for early retirements and a $7 million gain on the sale of three planes, net income was $339 million, or 89 cents a share.

Because United disclosed the revenue issue on July 24, some analysts hadn’t computed that change as part of their estimates, Wolfe Trahan’s Keay said in an interview. Costs came in higher than expected, he said, led by labor expense.

Spending for fuel, the airline’s largest cost, rose 5.6 percent to $3.41 billion. United paid $3.30 a gallon under contracts that lock in prices in advance, more than the $3 average spot price in New York Harbor after rates fell more than 5 percent from a year earlier.

Revenue Gain

Passenger revenue from each seat flown a mile increased 1.8 percent, compared with 8.5 percent at Delta Air Lines Inc., 5.8 percent at US Airways Group Inc. and 3.7 percent at Alaska Air Group Inc., which reported second-quarter earnings today.

“We are seeing demand being relatively stable,” Chief Revenue Officer Jim Compton said. “When we talk about the economy being tepid, we are very much aware of, particularly Europe, and are keeping our eyes on that. We’re obviously watching softness in the economy to see where that turns.”

Analysts have been tracking airlines’ revenue data for any signs that a slowing U.S. economy has crimped demand and the carriers’ ability to raise fares.

US Airways fell 3.8 percent yesterday following executives’ comments about slower growth in revenue from each seat flown a mile in July. That erased an earlier gain after the Tempe, Arizona-based airline said second-quarter profit tripled, and helped erase an advance for the Bloomberg airline index.

Delta Drops

Thursday’s decline in the airline index matched the longest such skid for the gauge of 10 carriers since June 2010, according to data compiled by Bloomberg. JetBlue Airways Corp. dropped 1.1 percent to $5.20, and Delta fell 0.6 percent to $9.41. US Airways rose 0.4 percent to $11.19 today, its second increase in the past trading nine days.

“With much of earnings season already behind us, we believe the market should not be surprised that higher fuel and sluggish demand trends are conspiring to trim (not devastate) 3Q consensus expectations,” Jamie Baker, a JPMorgan Chase & Co. analyst in New York, said today in a note to clients.

United said today that July passenger unit revenue will be unchanged from a year earlier. It is decreasing capacity across the Atlantic for the third quarter and full year, while Delta earlier said it’s trimming flying to Europe by 5 percent after Labor Day.

Limiting the supply of available seats helps airlines retain pricing power. United said today its fleet of 1,250 planes, including regional operations, will stay at about that level during the next five years.

Alaska Air said profit grew 24 percent, excluding special items, to $110.8 million, or $1.53 a share, from $89.6 million, or $1.22, a year earlier. Analysts had forecast $1.51.

Including costs to reduce the value of fuel purchase contracts, the Seattle-based company’s net income more than doubled to $67.5 million, or 93 cents, from $28.8 million, or 39 cents.

“Despite ongoing concerns about the macro economic environment, demand during the quarter was strong,” CEO Brad Tilden said on a conference call. Sales climbed 9.3 percent to $1.21 billion.