Delta’s slowing growth is leading to flights with fewer empty seats.

Delta Air Lines said Friday that traffic rose 2.4 percent in September while its capacity, measured in seats times miles flown, grew less than one percent. That is the smallest increase in capacity since Delta shrunk slightly in February 2014, according to company statements.

With the slower growth in tickets for sale, the average flight last month was 85 percent full, compared with 83.7 percent in September 2014. The figures include Delta Connection flights that use smaller planes. Capacity on those regional flights declined 5.6 percent.

For several years airlines clamped down on capacity growth, helping to boost average fares. But prices have fallen in recent months as the carriers added more flights and bigger planes. Investors have grumbled about the lower fares, and many airline stocks have drifted lower this year after huge gains in 2014.

Delta said that a key measure, revenue for every seat flown one mile, dropped by 5 percent last month compared with September 2014. It blamed lower average U.S. fares, the strong dollar hurting foreign revenue, and lower fuel surcharges on international flights.

The Atlanta airline said the revenue ratio would sink by between 4.5 percent and 5.5 percent for the entire third quarter, which ended Wednesday. That was slightly better than the decline of 4.5 percent to 6.5 percent that the airline had predicted.

Photo Credit: A Delta Air Lines plane taxis at Minneapolis St Paul International Airport. m01229 / Flickr