Hawaiian Airlines saved $220 million from plunging jet fuel prices in 2015 and said it used the money to help pay down more than a billion dollars in debt rather than reduce airfares.

The parent of the state’s largest carrier, Hawaiian Holdings Inc., reported Tuesday that net income more than tripled to $37.9 million in the fourth quarter as fuel costs declined $60.2 million in the last three months of 2015 from the same time in 2014. For the year, Hawaiian’s earnings more than doubled to $182.6 million.

Hawaiian said it expects to save $36 million in fuel costs this quarter and $140 million in 2016. The airline estimates its fuel cost in the first quarter will be in the range of $1.50 to $1.60 per gallon and for the year to be $1.35 to $1.45.

“People have not realized we are spending all of our profitability (in 2015) on paying off the debt that we accumulated while we’ve grown and hired thousands of employees, started new services and increased our financial contribution to the community,” Hawaiian President and CEO Mark Dunkerley said.

“When we made the decision half a decade ago to borrow a lot of money, that was a very substantial risk. Just like anybody who decides to, say, move into a house in a better neighborhood, school district or whatever to improve things for their family, the first thing they’re going to do when they work hard and get a little extra money, or get a pay raise, is to pay off their mortgage to decrease some of the overhang on some of their personal finances. That’s exactly what we’re doing at Hawaiian.”

Hawaiian’s adjusted net income in 2015 was a company record $189.3 million, and the airline used all of that profit and more — $195 million in total — to reduce its debt and strengthen its balance sheet.

Revenue was virtually flat for the quarter and the year at $574.2 million and $2.3 billion, respectively.

As fuel prices have decreased, domestic fares over the last two to three years have been flat to down, Dunkerley said.

“The fares you see are the fares that the market dictates,” he said.

“When fuel prices go up, we don’t increase fares,” he added. “We’ve never been able to increase fares to cover the cost of fuel prices going up. If you look at where our (neighbor island) fares are over the last 10 years relative to the growth of fuel prices, it’s essentially the same.”

Pasadena, Calif.-based financial adviser John Reardon, a longtime follower of Hawaiian, said the carrier has some of the longest flight distances of any U.S. airline and has been a prime beneficiary of lower fuel prices “since airfares have remained strong through the decline.”

“Recently, with the advent of Virgin America coming to the Hawaiian markets, fares from the mainland have moderated,” Reardon said. “What used to be a $600 round-trip coach fare is now more like $400 to $500.”

Dunkerley said he expects 2016 to be a better year for Hawaiian due to solid demand from all its markets, manageable competitive growth in routes to Hawaii, improving foreign exchange rates, increased sales from value-added products and lower oil costs.

”The big question going forward is, How much more capacity can the Hawaiian market absorb?” asked Reardon. “In the last economic slowdown of 2007 to 2008, demand for air travel to Hawaii remained strong. However, since then capacity has approximately doubled, and I suspect that an economic slowdown here on the mainland will have an adverse effect on demand and, by extension, pricing.”

Hawaiian expects capacity from the mainland to Hawaii to grow just 5 percent in the first quarter and decline 1 percent in the second quarter.

“Having had 18 months of double-digit capacity growth, we’re entering into a period of slow to slightly negative capacity growth,” Dunkerley said. “Over the course of the last couple of years, we’ve been out there saying that we thought there was perhaps a little bit of irrational exuberance about the overall level of capacity in the marketplace in the past. So what we’re looking at at the moment feels to us more like a normal situation than it does an especially constrained situation.

“But again, these are markets without any real barriers to entry. Other carriers will be making their own network decisions independently, and all we’re sharing, is the way we see it. Time will tell how they see it.”

Hawaiian’s stock ended Tuesday up 73 cents, or 2.3 percent, to $32.35. The financial results were announced after the market closed.