After a month of construction, Des Moines International Airport has reopened its main runway. So, you pilots out there, check with the tower and try out the new pavement. Or at least pause to admire it when you are taking off and landing on your favorite commercial carrier. These things don’t come cheap: The airport spent $15.5 million on just the second part of the construction, which will be a $45.7 million deal for the three phases. The main runway is called 13/31 and runs southeast to northwest. It will be completed next fall. The airport also is installing a lighting system that will help parkers know the status of each stall — red for occupied, green for vacant, and blue for stalls intended for vehicles carrying people with disabilities who have a special permit. The lights will be in the long-term parking garage by next fall.