Troubled Spirit is the seventh-largest operator in the United States by seats for sale in the second quarter of 2025. Given the country's vast short-haul domestic and international operations, Cirium Diio data shows that the carrier, which recently exited bankruptcy protection, has less than 4% of the market.

The latest network development is that Spirit has added 15 routes from Detroit. The airline's considerable nationwide growth in the past two decades meant Detroit seats for sale fell from 35% of its total in 2004 to 10% in 2019 and 7% in 2024. Spirit's new routes may mean that the share will increase in 2025.

Spirit adds 15 Detroit routes

As first identified by Ishrion Aviation, Spirit's additions are as follows, with mainly sub-daily frequencies as is usual for such operations. However, two routes—Detroit to Hartford and Phoenix—will be flown daily. All 15 routes will begin in May or June, with some starting with relatively little advanced notice.

When most carriers reveal a slew of links, they have served several of them before, as is the case here. However, nine routes will be new to Spirit's map, including the two shortest additions: Detroit to Milwaukee and Louisville.

Five more Detroit routes are coming

Aside from the 15 airport pairs discussed above, Spirit will also introduce or resume flights to the following destinations, all of which were previously revealed:

• Baltimore: returns on May 8 (four weekly); last flown in 2023
• Charlotte: starts on May 8 (four weekly); new to network
• Memphis: begins on May 8 (four weekly); new to network
• Raleigh/Durham: resumes on May 8 (twice-weekly); last flown in 2020
• San Antonio: starts on May 9 (twice-weekly); new to network

That makes 40 Detroit routes (for now)

Spirit's schedule submission to Cirium Diio is currently available until August 2025. It plans 40 Detroit routes between May and August, far more than available in any full year. Indeed, examining every service since 2004 shows Spirit has not had more than 27 airport pairs from the Michigan airport (until now).

Below is Spirit's entire network between May and August 2025. Spirit will face Delta on all of them, with other carriers on a handful. Unlike Delta, for example, Spirit's targeted passengers will trade off inconvenience (of schedule, frequency, or both) and a different product for lower fares.

As always, Spirit must meaningfully increase point-to-point traffic on its new routes. Consider Louisville, just 266 nautical miles (493 km) away, which the carrier will fly twice-weekly.

The US Department of Transportation shows that Louisville had just 57 passengers daily each way in the 12 months to July 2024. Delta serves it up to four times daily, with an average local fare (across all passengers and cabins) of $242 one-way.

As is usually the case, Spirit has more seats to Orlando than anywhere else. The Delta hub-to-hub route to Atlanta is next, followed by Fort Lauderdale, Las Vegas, Tampa, Los Angeles, New York LaGuardia, Dallas/Fort Worth, Houston Intercontinental, and Fort Myers.