Shares of Republic Airways Holdings Inc. enjoyed a 22-percent rocket ride on Monday after a stock analyst gave the beleaguered airline an upgrade and as the price of jet fuel crept downward.

The Indianapolis-based airline also took a step forward on its integration of two recently acquired airlines, as a key pilots union decided to join the Teamsters.

Republic’s stock closed Monday at $5.67, up more than $1 per share from last week. The stock gave back nearly 6 percent of that gain in trading Tuesday morning, trading as low as $5.33 per share.

Republic, which built up a profitable business flying point-to-point routes for larger airlines, has stumbled since buying two scheduled-service carriers in 2009. It is still trying to integrate the operations of Denver-based Frontier Airlines and Milwaukee-based Midwest Airlines, all under the Frontier brand.

Those scheduled-service airlines now represent 60 percent of Republic’s business and led the company to a $22.4 million loss in its first quarter. As IBJ reported Monday, many analysts and investors have grown sour on the deal.

Republic also has been staggered by a run-up in jet-fuel prices that were about 50 percent higher this spring than the previous year. Republic has not hedged its fuel costs as much as some other airlines and, therefore, is more susceptible to price spikes.

But prices have been coming down, along with crude oil prices, giving Republic some relief. The shift caused Evercore Partners analyst Duane Pfennigwerth to issue a new forecast Monday, saying he now expects Republic’s 2012 earnings per share to be 90 cents, way up from his previous estimate of 35 cents.

The difference is almost entirely due to Pfennigwerth’s estimate that fuel prices will average $3 per gallon next year, instead of his previous estimate of $3.20 per gallon.

“RJET has the highest fuel leverage across our coverage list,” said Pfennigwerth, referring to Republic by its stock ticker symbol. “Small changes in fuel price assumptions drive large changes in EPS.”

Pfennigwerth, who is based in New York, said Republic’s stock price could hit $9 per share in a few months. He also praised Republic’s progress on reducing costs in its Frontier operation.

A big step came June 10 when Republic won pay freezes and benefits cuts from pilots, in exchange for an equity stake in Frontier. The agreement Monday for the pilots unions from Midwest and Frontier to jointly have Teamsters representation clears up what has been a major distraction for Republic’s management.

Also, it was reported last week that Republic had ordered 80 new jets from France-based Airbus and Montreal-based Bombardier, which will be more fuel-efficient than some of its current fleet.