On Tuesday, JetBlue Airways (JBLU -18.77%) held its biennial investor day. The company's presentation touched on a wide variety of initiatives -- many of them cost-related -- that could help JetBlue grow its earnings during the next several years.

However, the most important earnings growth driver that JetBlue talked about is the ongoing rollout of its Mint premium service. JetBlue's take on business-class service is generating huge profits on routes that had been perennial underperformers. Moreover, Mint has a huge runway for growth in the coming years.

Mint crushes expectations

In 2013, JetBlue announced that it intended to fly specially configured A321s on its routes from New York to Los Angeles and San Francisco. Each plane has 16 flat-bed seats in the "Mint" premium cabin -- four of which convert into semi-private suites -- along with 143 coach seats.

JetBlue introduced its first flat-bed premium seats in 2014. Image source: JetBlue Airways.

At first, many analysts were skeptical. Some questioned whether JetBlue could win business travelers away from larger competitors like American Airlines (AAL -2.06%) and Delta Air Lines (DAL 0.43%). Others suggested that JetBlue couldn't charge enough for its Mint seats to justify the added costs. Still others argued that Mint might succeed in its two initial markets, but it wouldn't work anywhere else.

Within less than a year, it became clear that Mint was a huge success. As a result, JetBlue has increased the Mint fare structure multiple times.

As the company expected, Mint proved popular with small business travelers and wealthy leisure travelers. However, it has also been surprisingly successful in catering to larger corporations that traditionally gave all of their business to legacy carriers like American Airlines and Delta Air Lines.

JetBlue provides some numbers

This week, JetBlue provided the most detail it has ever offered to quantify the financial impact of Mint. Before Mint's introduction, JetBlue's New York-Los Angeles route was significantly less profitable than the system average -- and the New York-San Francisco route was even worse.

However, in the course of two years, the LA route's profit margin improved by 17 percentage points relative to the system average. The San Francisco route's profit margin improved by 18 percentage points. This has made them two of JetBlue's most profitable routes.

Interestingly enough, JetBlue achieved these results while doubling its capacity on both routes. (Typically, increasing capacity by this magnitude would drive fares down, hurting profitability.) JetBlue found that increasing its flight frequency in these highly competitive markets has helped it attract more business travelers, even in the coach section.

JetBlue has doubled its flight schedule on its first two Mint-equipped routes. Image source: JetBlue Airways.

Based on JetBlue's estimates, going from five daily roundtrips on the A320 to 10 daily roundtrips on the A321 for the New York-Los Angeles route has increased the profit margin of the coach section by a stunning 14 percentage points.

Mint growth continues

Seeing this success, JetBlue decided last year to expand Mint to its Boston-San Francisco and Boston-Los Angeles routes. JetBlue recently completed the conversion of both routes to the Mint configuration, and they are producing promising results.

The Boston-San Francisco route -- which got Mint service beginning in the spring -- has already seen a significant improvement in its profit margin relative to the system average. Next summer, JetBlue will add a fourth daily Boston-San Francisco flight, to meet rising demand.

In 2017, JetBlue will accelerate the growth of Mint. The Mint-equipped fleet will nearly double in size next year, allowing JetBlue to upgrade several more routes to Mint service, including Fort Lauderdale-Los Angeles, Fort Lauderdale-San Francisco, and New York-San Diego.

During late 2017 and early 2018, JetBlue will add Mint service on several more transcontinental routes: Boston-San Diego, New York-Seattle, Boston-Seattle, and New York-Las Vegas.

The rapid growth of Mint over the next year and a half could put pressure on unit revenue at both Delta and American. One or both of those carriers serve each of the routes that are on tap to receive Mint service. JetBlue will undercut Delta Air Lines' and American Airlines' first-class fares, while being the only airline to have a 100% flat-bed premium cabin on those routes. That's a recipe for market share gains by JetBlue.

The rollout of Mint may force Delta to cut its transcontinental first-class fares. Image source: The Motley Fool.

The opportunity is enormous

JetBlue executives have acknowledged that Mint won't be as profitable in every market as it has been on the handful of routes where it is already deployed. Nevertheless, JetBlue has plenty of other transcontinental markets where Mint service might be feasible.

Additionally, as Mint grows in popularity, JetBlue should be able to increase flight frequencies on many of the routes scheduled to receive Mint service in 2017 and 2018.

Most importantly, Mint could be JetBlue's ticket to transatlantic expansion. During the investor day presentation, JetBlue management noted that the most important business market that JetBlue doesn't serve from Boston is London. An all-coach product might not work well for flights to London, due to the high cost of operating there. On the other hand, Mint seems ideally suited to the New York-London and Boston-London markets.

JetBlue will need to buy the A321LR if it wants to serve Europe. That plane won't be available until 2019. Thus, American Airlines and Delta Air Lines don't have to defend that lucrative piece of turf just yet. But a few years from now, JetBlue could expand Mint's reach even further, disrupting its larger competitors once again.