The main runway at Portland International Jetport closed Monday for a $13.7 million project that involves repaving and installation of new LED lighting.

The 56-day closure required flight operations to shift to a secondary runway on Monday, causing a change in air traffic patterns over Portland, South Portland, Scarborough and Westbrook, officials said.

The airport’s instrument landing system will be down, which could lead to flight delays or cancellations in times of low visibility, officials said.

The period when the intersection between the two runways is repaved from May 16 to June 13 will result in reduced hours of operation, with no flights from 10:30 p.m. to 5:45 a.m.

Workers have begun the process of removing electrical components and removing runway asphalt.