A new survey suggests that air travel is slowly improving, led by a small group of airlines.

Passengers who fly JetBlue Airways and Southwest Airlines had the highest satisfaction rating — 800 and 781, respectively, out of a possible score of 1000, according to J.D. Power’s latest North America Airline Satisfaction study.

Overall passenger satisfaction with major airlines increased to 717 out of a possible score of 1000 in 2015, up from 712 a year ago, according to J.D. Power’s study.

Here are some of the major findings:

• The worst airlines for customer service are United Airlines (665) and Frontier Airlines (659).
• The most improved carriers are American Airlines and Delta Airlines, adding 16 points each.
• WestJet fell by the most, plummeting 19 points from 2014.
• Spirit Airlines, a perennial worst, was omitted from the survey. There weren’t enough responses from passengers. But if J.D. Power had included the airline in the survey, it would have ranked dead last with a score of 629.

The study gauged passenger satisfaction among both business and leisure passengers in several key areas, including costs, fees, in-flight services, onboard experience and reservations. It was conducted between April 2014 and March 2015. J.D. Power distinguishes between “traditional” and “low-cost” carriers in its ranking, but Fortune combined them for this report.

The findings reflect another recent study on airline service, which also suggested airline service was trending higher.

To put these scores into a little perspective, the top-ranked airline would receive an equivalent letter grade of “B-.” The highest-scoring legacy carrier, Delta Air Lines, would get a “C-.” The lowest-ranked carriers receive a grade of “D,” according to its customers.

Airlines still rank below banks and mortgage lenders, two other industries covered by J.D. Power. “Airline customer service experience is low,” says Rick Garlick, global travel and hospitality practice lead at J.D. Power. “But it’s getting better.”

What the findings mean for customers

J.D. Power says the findings show that customer service matters, perhaps now more than ever. In its view, the airline industry is evolving from a commoditized transportation business into a business focused on hospitality and services.

“The carriers most focused on providing a pleasant experience are being rewarded with higher customer satisfaction and loyalty,” says Garlick.

He says the study suggests that when passengers make the decision to fly an airline based on the services or experience the airline provides, rather than price, convenient routes and scheduling, satisfaction is higher and passengers are more likely to return to the airline brand and to recommend it to others.

But there’s another reason for the uptick in scores, and they have nothing to do with better service.

“People have adapted to the airline fees that use to upset them,” adds Garlick. “So it might be more accurate to say people are less dissatisfied.”

A closer look at the J.D. Power numbers shows how various airlines succeeded — and failed.

American and Delta surged ahead by investing in their customer service infrastructure and training, with an emphasis on high-revenue business travelers. Alaska’s downward swing can be explained by some of its growing pains, as it expands to new cities where passengers are less familiar with the brand. And the failure of airlines such as United and Frontier? Garlick says those airlines have focused on low fares and high fees, to the detriment of customer service.

“Everyone wants low-cost travel,” he adds. “But there’s a price to be paid for it. The low-ranked carriers are running their companies so frugally that not even their core customers are satisfied. They’re willing to pay for a better experience.”

A long way to go

Critics agree that airline service still has a way to go before it can be considered good. “As the airlines have been complaining that customers are treating their seats like commodities, the airlines themselves are treating their passengers — except frequent flier elites and first class — like self-loading cargo,” says Charlie Leocha, president of Travelers United, an advocacy organization for air travelers. “Onboard services have been ratcheted back, extra and exorbitant fees are being loaded on passengers, and legroom and seat sizes continue to shrink.”

Leocha says investing in customer service doesn’t have to be expensive. A simple smile from flight attendants or gate agents, waiving a standby fee to get on an earlier flight with empty seats, allowing families to sit together without paying more, all make the travel experience far more pleasant.

“Unfortunately,” he adds, “these amenities still seem to be in short supply.”