United Airlines' shares have hit a record high, a dramatic turnaround for the third-largest U.S. airline that has weathered a rash of public relations disasters and investors who fretted the carrier's growth plan would spark a fare war with competitors and a surge in expenses.

United Continental Holdings' stock closed at an all-time high of $89.58 on Thursday and shares of the third-largest U.S. airline's parent were on track to hit another record Friday, trading up 0.7 percent around 3 p.m.

The carrier's stock this year is up more than 33 percent — more than any other U.S. airline — and a bigger percentage gain than the S&P 500, which is up 8 percent in 2018. American Airlines shares are down more than 23 percent, while Delta Air Lines is up 3.5 percent this year.

The share-price surge comes after a series of public relations fiascoes, including the violent dragging of passenger David Dao off of a United Express flight in April 2017. A series of high-profile incidents in which passenger pets died while in United's care, such as the French bulldog puppy that had been placed in an overhead bin in March, again put United on the defensive to calls of #boycottunited on social media.

Investors in January sent United's stock tumbling 11 percent, as executives struggled through the second tense earnings call in a row, that time explaining an aggressive growth plan to expand as much as 6 percent a year.

"They were in the doghouse from the market's perspective," said Jamie Baker, senior airline analyst at J.P. Morgan Chase.

While Delta and American cut their profit outlook for this year in July, United raised its estimate. United said it was recovering most of a profit-crimping surge in fuel costs through higher fares and other initiatives. Higher fuel prices have challenged airlines in a period of strong demand.

On Monday, United said it expanded flying 4 percent this year through August, and that its planes were flying more than 84 percent full, slightly higher than a year earlier.

"We think they're back where they want to be," said Susan Donofrio, airline analyst at Macquarie.