Warning: SFO’s most important runway about to close

Frequent flyers beware: Starting September 7 the most frequently used runway at San Francisco International Airport (SFO) will close for 20 days to allow a $17.2 million fix-it job aimed at keeping the critical piece of transit infrastructure from potential failure in the future.

As runway 28L is SFO’s most important takeoff and landing site, the closure will mean major delays for potentially any flight coming into or out of the Bay Area’s busiest airport, although those on red-eye flights may avoid the worst of it.

SFO announced the closure in March, citing the need for critical repairs:

The project will reconstruct a 1,900-foot section of Runway 28L, replace lighting and drainage infrastructure, and overlay a 600-foot section of Runway 1L.

SFO repaved the entire top layer of Runway 28L in spring 2017. During this project, core sampling and ground-penetrating radar indicated that the base layer was showing signs of fatigue cracking due to the large amount of aircraft activity in this area. [...] SFO staff have evaluated multiple options and concluded that the best long-term solution is to excavate the section of Runway 28L at the intersection of Runway 1L and 1R to reconstruct the pavement structure.

SFO estimates that some 68 percent of flights utilize this key runway intersection.

This same intersection was where SFO had to repair a “12-inch depression” in April, causing major delays.

To give some idea of the scope of the potential for delays during the closure, SFO closed both 28L and 1R for repairs in September of 2018. That closure lasted less than 48 hours, but the San Francisco Chronicle later reported more than 600 flights affected.

According to a Field Guide To Airport Pavement Maintenance published by the Washington DC-based non-profit the National Academy of Sciences, fatigue cracking, which is the result of regular stress from constant plane traffic, “is considered a major structural distress.”

“The cracks propagate to the surface initially as a series of parallel cracks. After repeated traffic loading, the cracks connect, forming many-sided, sharp-angled pieces that develop a pattern resembling chicken wire or the skin of an alligator,” hence they’re also sometimes called alligator cracks.

If left unrepaired, such cracks can eventually cause “foreign object damage” to planes during takeoff and landing.

The 20-day closure date was picked to fall between the summer and holiday travel rushes and before heavy rains become more likely in the peninsula.

The March closure announcement advises, “SFO recommends that travelers opt for early morning flights before 9:00 a.m.,” as the lighter traffic during late-night and early morning periods makes delays less likely.

In September 2018, SFO served more than 4.65 million passengers, and more than 4.73 million in September 2017.