JetBlue Airways (JBLU -0.31%) had fairly modest expectations for its upscale Mint service when it launched less than three years ago. Wall Street analysts were also doubtful about JetBlue's ability to win over well-heeled travelers who would pay $600 or more for a flat-bed seat on transcontinental routes.

Instead, Mint has been an amazing success. In addition to attracting wealthy leisure travelers and small/medium business customers, JetBlue's Mint service has made inroads among corporate travelers who had previously been loyal to legacy carriers like Delta Air Lines (DAL 0.17%).

The interior of the JetBlue Mint premium cabin

Demand for JetBlue's pricey lie-flat seats has been very strong. Image source: JetBlue Airways.

This success has encouraged JetBlue to add more and more Mint flights. Last week, the carrier divulged its latest plans to expand its Mint service.

New routes for New York

Mint began in 2014 with two routes: New York-Los Angeles and New York-San Francisco. American Airlines, Delta Air Lines, and United Continental all serve those routes with specially configured planes featuring flat-bed business class seats, and JetBlue was finding it hard to compete without a comparable product.

The launch of Mint spurred a huge increase in demand. Before JetBlue introduced its premium offering, it operated five daily flights to Los Angeles and three to San Francisco. In the next two years or so, JetBlue doubled its capacity on both routes while turning them into two of its most profitable routes -- whereas they had been underperformers prior to 2014.

In the past few years, JetBlue has added Mint flights from New York to popular destinations in the Caribbean, but most of these are Saturday-only service. However, later in 2017, JetBlue will start adding new West Coast destinations for its Mint flights from New York, as part of a big Mint expansion announced a year ago.

A JetBlue plane

Mint has already had a noticeable impact on JetBlue's profitability. Image source: JetBlue Airways.

First, JetBlue will convert its two daily flights to San Diego to Mint service. The company had already announced one daily Mint flight between New York and San Diego that will start in mid-August; the second Mint roundtrip will begin in October.

Second, in early November, JetBlue will start using Mint-equipped planes for two daily roundtrips to Las Vegas. JetBlue offers three to five daily flights on this route, but for now it will operate a mix of Mint and non-Mint flights between New York and Las Vegas.

The Boston expansion continues

Seeing the huge success of Mint in New York, JetBlue expanded its premium service to its Boston-San Francisco and Boston-Los Angeles flights last year.

Arguably, the stakes are even higher in Boston. JetBlue is the largest airline there, operating roughly 150 daily departures. This gives it an opportunity to become the airline of choice for Boston-based business travelers. In the past six months, it has tried to solidify its position in Boston by launching two key new routes that are popular with business travelers, with up to six daily flights to New York's LaGuardia Airport and five daily flights to Atlanta.

However, Delta Air Lines is also growing in Boston. It will operate 90 peak-day departures there by this summer, serving a mix of business and leisure destinations. In June, Delta will begin competing with JetBlue on the Boston-San Francisco route, and it recently announced that it will use planes equipped with flat-bed seats in the premium cabin for those flights.

A Delta Air Lines plane

Delta is trying to challenge JetBlue's supremacy in Boston. Image source: Delta Air Lines.

Expanding Mint service in Boston is a good way for JetBlue to stay a step ahead of Delta. Last fall, it decided to add a fourth daily Mint flight on the Boston-San Francisco route beginning in July. This week, it announced that it will add a fourth daily Mint flight from Boston to Los Angeles in late October. By offering more schedule choices on these key routes, JetBlue should be able to gain market share among business travelers.

JetBlue will also launch twice daily Mint service from Boston to San Diego in December. This will be the fifth new Mint route of the seven that were announced last year. And JetBlue confirmed that New York-Seattle and Boston-Seattle are still in line for an upgrade to Mint service -- presumably in early 2018.

Mint will accelerate JetBlue's profit growth

After posting huge earnings increases from 2014 to early 2016, JetBlue's profit growth has ground to a halt. In fact, analysts expect earnings per share to plunge almost 20% year over year at JetBlue in 2017.

JBLU EPS Diluted (TTM) Chart

JetBlue Airways EPS Diluted (TTM), data by YCharts.

Recent capacity changes should allow JetBlue to stabilize its earnings as the year progresses. The rapid expansion of JetBlue's popular Mint service that is just starting will then help to drive a return to strong EPS growth in late 2017 and especially during 2018.

By the first half of next year, Mint flights could account for 20% or more of JetBlue's capacity, up from just 11% last quarter. If JetBlue's first handful of Mint routes are any guide, this growth of its premium offering will have a transformative effect on the company's profitability.