ALASKA AIRLINES flew 340.4 million revenue passenger-miles in May, up 13.8 percent from 299 million flown in May 1989.

Load factor for the Seattle-based airline was 50.2 percent in May, down

from 50.9 percent in the same 1989 month.For the five months ended in May, RPMs totaled 1.6 billion, up from 1.4 billion a year earlier. Load factor for the five months was 49.4 percent, down

from 50 percent in the year earlier period.

UNITED AIRLINES flew 116.7 million cargo ton-miles in May, up from 111.5 million a year ago. Revenue passenger-miles for the Chicago-based airline increased to 6 billion from 5.6 billion in May 1989. Load factor was 63.4 percent, compared with 62.6 percent a year ago.

Cargo ton-miles totaled 539.5 million during the first five months of 1990, up from 525 million in the same 1989 period.