More than 1,100 flights have been delayed or cancelled at San Francisco International airport since the airport closed its busiest and second-longest runway, 28L, to construct a new base layer below the runway surface.

The closure, which began on 7 September and is due to last until 27 September, has frustrated thousands of travelers and caused chaos at one of the busiest airports on the West Coast.

In a statement, the airport says airlines have tried to alleviate some of the pain in advance by implementing voluntary schedule adjustments. This resulted in total flights being reduced by 13% during the 20 days of the Runway 28L closure.

Airlines have also re-timed certain flights to reduce demand during peak times.

Still, thousands of passengers have suffered through the disruption as construction crews reconstruct the runway which had been repaved just two years ago.

During the project at that time, engineers discovered “the base layer was showing signs of fatigue cracking due to a large amount of aircraft activity in this area”, the airport says in a statement.

They were not able to address the issue at that time, so further repairs had to wait until this month.

The total length of Runway 28L is 3,469m (11,381ft). The project will reconstruct a 579m section of Runway 28L, replace lighting and drainage infrastructure, and overlay a 183m section of Runway 1L.

Runway 28L is used primarily for arriving flights, with Runways 1L and 1R mainly used for departing flights. The intersections are the most heavily travelled areas of the entire runway system at San Francisco, with more than 68% of flights crossing these intersections, the airport adds.

During the closure in July 2017, pilots of an Air Canada flight arriving from Toronto at night narrowly averted disaster when they mistook a taxiway to the right of the active runway 28R for the runway itself.

Four fully occupied long-haul aircraft were holding short on the taxiway as Air Canada 759 approached from the southeast. With seconds to spare, the Air Canada crew executed a missed approach, passing less than 20ft over the parked aircraft. The aircraft landed without incident on 28R on its second approach.