There have been rumors of Air Koryo offering more flights than ever before for 2013, but now there is confirmation. Confirmation being a notice on the door at Sunan Airport. As of mid-April, Air Koryo will be running flights to Beijing on Monday and Friday as well as its regular Tuesday/Thursday/Saturday flights. This will bring them into direct competition with the Air China flights on those days, which are more expensive. Moreover, Air China seems to run the route quite reluctantly, especially in the winter, when any dusting of snow seems to be a pretext for cancellation. Its not hard to see why: during the winter months, capacity is very low.
Anyway, the Air Koryo flight schedule is below: