MINNEAPOLIS – Delta Air Lines is shrinking its flying to small cities in the nation’s midsection, saying it can’t make money on flights that are sometimes empty.

On Friday, Delta said it would adjust flying in 24 cities, many of which are not served by any other airline. There’s a risk they could lose air service altogether, although some of the routes are likely to be taken over by regional airlines. And Delta said it will ask for a federal subsidy to keep some of the flights.

The affected flights connect Delta’s hubs to small cities in rural Iowa, Michigan, Minnesota, Mississippi, North Dakota and South Dakota. Indiana and Ohio markets were not on the list.

Most of the affected flights are on Delta’s 34-seat Saab turboprops, which the airline is phasing out by the end of this year.

Higher fuel prices have made it difficult to operate small planes profitably because the fuel bill is divided among a small number of passengers. Even the next-larger option, 50-seat regional jets flown by Delta and other airlines, is often unprofitable for the same reason. Delta is retiring many of those planes too.

Delta said it is losing $14 million a year on the flights included in Friday’s announcement.

Their occupancy averaged just 52 percent, compared with a systemwide average of 83 percent last year. The average occupancy out of Thief River Falls, Minn., was just 12 percent, Delta said. The flight from Greenville, Miss., runs just 27.6 percent full. Some flights have been completely empty, it said.

Flights in 16 of the cities on Delta’s list are subsidized by the federal Extended Air Service program. Under the program, the Transportation Department solicits bids from airlines to see how much money it would take to get them to serve a particular city.