JetBlue (JBLU) - Get Report shares have traded flat this year, but the carrier seemed to impress investors at its investor day, when it touted better-than-expected fourth-quarter unit revenue trends, an enhanced stock repurchase program and a plan to reduce costs.

Shares fell Wednesday to $22.15 and have declined 2% year to date. The stock gained 4% on Tuesday.

JetBlue may be a New York-based airline, the biggest carrier at John F. Kennedy International Airport, but on Tuesday the focus was on Boston Logan, which is where the carrier's growth is.

Logan was the nation's 17th-busiest airport in 2015, but it was the third-busiest non-hub airport, and JetBlue has grown into its No. 1 carrier, with about 30% of the domestic traffic, a presence in 39 of the top 50 markets, and rapidly improving profit margins.

JetBlue next year will have has 42% of capacity in New York, 21% in Boston, 15% in Fort Lauderdale, Fla., and 8% in both Orlando and Los Angeles/Long Beach. Ten year ago, it had 56% of capacity in New York, 14% in Boston, 11% in Los Angeles/Long Beach,  7% in Fort Lauderdale and 6% in Orlando.

Over the past three years, JetBlue's overall operating margin has been growing (operating margin was about 20% in the September quarter), but margins in Boston have significantly exceeded system margins, according to a chart displayed by Scott Laurence, senior vice president of planning.

Since 2014, Boston margins have been more than twice the system margin, the chart showed.

For JetBlue, Boston offers proof that the theoretical "S Curve" concept might actually work. S Curve describes the growth of a variable in relation to another variable, in this case Boston margin to system margin. Also, it starts with modest growth, defined in the lower part of the S, and then accelerates, as seen in the upper part.

"The S curve hasn't ever worked {but} it's actually working for us," said Laurence, who noted he has been in the airline industry for 20 years (he started at USAir) and the S Curve "never works as well as it has worked in Boston."

In Boston, JetBlue has benefited from getting to critical mass, as more routes mean more loyalty.

Early on in Boston "we were like a grocery store that didn't sell milk," Laurence declared. Key steps came when the carrier added Boston-Atlanta in March and Boston-LaGuardia in October.

An illustration of the law of unanticipated consequences is that Boston-Pittsburgh is now among JetBlue's top five most profitable routes. An intended consequence is that walkup fares for Boston-LaGuardia declined from $434 to $129, said CEO Robin Hayes, who added: "The spirit of disruption and innovation is truly alive at JetBlue."

One growth area for JetBlue has been business travelers, a change for an airline that started with a leisure focus. JetBlue and Boston are compatible, Laurence noted. JetBlue is not a traditional hub airline and Boston is a city without an airline hub. (Ironically, Boston is sometimes called "the hub.")

"Network airlines talk about optimizing connectivity and moving banks around," Laurence said. "We focus on large local markets. Our customers are very happy with the concept of non-stop flying."

What's next for Boston? JetBlue growth, obviously. For reference, here is a list of the 11 busiest markets that JetBlue does not serve from Boston: Columbus, Ohio; Indianapolis; Kansas City; Milwaukee; Minneapolis; St. Louis; Toronto; Dublin; London Heathrow, Paris and Reykjavik, Iceland.

Laurence focused on just one. "The largest unserved market that drives the most relevance is London," he said.

JetBlue has said repeatedly that it is looking at the long-range version of the Airbus A321, which would have the capability to fly trans-Atlantic. Discussion on the investor day call did nothing to dispel the impression that Boston-Heathrow would be the first route, even though British Airways, Delta, and Virgin Atlantic already fly the route while Norwegian Air flies Gatwick-Boston.

As for Fort Lauderdale, when JetBlue looks at Fort Lauderdale-Hollywood International Airport, it sees another Logan -- another airport where it should grow.  "We believe strongly that {South Florida} is an underserved market," Laurence said. "We have the same aspiration that we do in Boston.

"We have a great RASM premium at Fort Lauderdale and {there is} room to grow" even as JetBlue moves to 140 daily Fort Lauderdale departures, he said, adding that much of JetBlue's planned 2017 capacity growth of 6.5% to 8.5% will be in Boston and Fort Lauderdale.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.