With tens of billions of dollars spent each year on aviation fuel, the recent drop in energy prices would seem to be a boon for airlines.

So why is at least one industry analyst worried?

It’s not because it’s thought that airlines will cut fares to match their reduction in costs. The airlines have made clear that isn’t going to happen.

But analyst Hunter Keay of Wolfe Research worries lower costs will prompt airlines to boost capacity unwisely and unprofitably. The industry returned to vibrant health after it throttled back its flying. Now, will it push the throttles forward?

But other analysts have offered different views, that companies would be wise to boost output if lower expenses allow it, or that there’s little sign capacity is getting out of hand.

In any case, the airline industry has shrugged off suggestions lower fuel prices should bring lower airfares, as John Heimlich, vice president and chief economist of trade group Airlines for America, explained in a conference call this month.

“The first priority is to make sure you have strong financial health, can pay down your bills and invest in the future and weather the next recession,” Heimlich said.

And, he noted: “We don’t really hear people clamoring for lower prices of cheeseburgers when the price of beef comes down or lower prices of iPhones when the price of semiconductors go down.”

On their third-quarter earnings calls, airline executives also made it clear they didn’t intend to pass on any energy savings.

“Air travel remains a great bargain,” American Airlines Group president Scott Kirby said. “We’ll continue to keep it a great bargain for customers. But in a strong demand environment, we don’t have plans to go off and just proactively cut fares.”

Southwest Airlines chairman and chief executive officer Gary Kelly said he’s worried about the volatility of fuel prices, even with the current drop in energy costs.

“You remember 1999. Crude oil I think went down to $10 a barrel, only to be followed with increases every single year for the next decade. It was just an unprecedented spike that took place. So, that’s what worries me,” he said.

Kelly said that airlines can’t count on raising fares when energy prices go back up, and pointed to 2008 as an example. “There was a very sharp spike in energy prices. All carriers tried to raise fares. Five went bankrupt and aren’t here anymore. So, no, the answer is absolutely not.”

Based on 2013 use of 15.9 billion gallons, each penny drop in jet fuel prices saves the U.S. airline industry $159 million annually. Consider the spot price of Gulf Coast jet fuel has dropped from $3 a gallon at the end of 2013 to less than $2.40 in recent days.

While that can add up to some big savings, Keay, the Wolfe Research analyst, has held to a theory that links higher fuel prices to the potential for higher airline profits.

When the economy is doing well, fuel prices tend to be higher, but more people will fly and will pay more to do so, he suggests. Higher fuel prices also keep airlines from investing in flights that are marginally profitable.

“We are increasingly uncomfortable with the longer term impact from lower oil prices as it relates to our investment thesis on airlines,” Keay wrote. “For years we’ve said high oil prices are good for airlines, so it would be intellectually dishonest to say low oil prices are also good for airlines.”

Keay noted a number of airlines have outlined plans to increase their flying in coming quarters. They’ve pegged their growth to the gross domestic product, saying they’ll grow at or below that rate. He is not reassured.

“We’re not sure who invented this but many now believe it represents a threshold of what’s acceptable,” Keay said.

He noted network airlines, which had cut their capacity in the face of high energy prices, grew their flying in the U.S. by 4 percent in late 2010 as jet fuel prices were lower and somewhat stable.

“Then oil prices went right back up again, as they tend to do, and 2011 stunk,” he said.

As of late October, he was looking at estimates that airlines again would boost their domestic capacity 4 percent in 2015. “We’d be fools to ignore this precedent and honestly rationalize it because jet fuel is cheap today,” Keay wrote.

Taking a different view is analyst Jamie Baker of J.P. Morgan.

He said it makes sense for companies like airlines to increase output — add capacity — if their input costs go down. If current prices hold steady, the industry’s fuel bill in 2015 would be $5 billion less than at previous jet fuel prices of $3.05 a gallon, he said.