ANN ARBOR, Michigan — How jittery are investors about airline stocks these days? Just ask United Airlines.

An erroneous report that flashed across trading screens Monday, saying United had filed for a second bankruptcy, sent its stock plummeting.

Shares fell to about $3 from more than $12 in less than an hour, wiping more than $1 billion in value before trading was halted. The stock closed at $10.92, down 11.2 percent.

By the end of the day, fingers were pointing in many directions to assign blame.

United blamed an old Chicago Tribune article that, it said, was posted on the Web site of The South Florida Sun-Sentinel. That article was picked up by a research firm, Income Securities Advisers, which then posted a link to it on a page on Bloomberg News, which sent a news alert based on the old article.