Alaska Airlines grew its reach again in May, but also watched its on-time performance continue to slip.

The mainliner under Seattle-based Alaska Air Group Inc. reported a 10.3 percent increase in traffic on a 12.1 percent year-over-year capacity increase, according to Air Group’s May operational report released June 2.

The passenger and capacity growth resulted in a load factor, or percentage of available capacity sold, decrease of 1.4 percent to 84.8 percent.

Year-to-date traffic is up 10.4 percent on a 12 percent increase in capacity for an 84 percent load factor.

While Alaska Airlines was the top major domestic carrier in on-time performance in the first quarter of 2015, according to the U.S. Department of Transportation, its monthly on-time numbers have now fallen for a full year.

The airline reported a 1.7 percent decrease in on-time arrivals versus May 2014, marking the 12th consecutive month the metric has weakened. Still, 88 percent of Alaska Airlines flights arrived on time in May.