A recent report by NBC Bay Area detailed the worsening runway problem of the San Francisco International Airport (SFO). Scientists refer to it as subsidence, which only means that SFO is slowly sinking.
The airport was built on a landfill, meaning its underground foundations are unstable. The increase in air and runway traffic over the past years has exerted too much pressure on the land beneath SFO, causing the surface to crack. The subsidence caused delays and cancellations of flights, burdening travelers. The repair days from January 2016 to January 2019 caused 31 canceled flights and 410 delayed ones.
An earth scientist found that the land SFO stands on is sinking at least 5 millimeters per year, which is a significant drop geologically. At this rate, the airport’s runways will be completely underwater by 2100. The runways are sinking at different rates, with those directly on top of the landfill cracking faster than the others. The different rates of subsidence result in horizontal stresses, and these cause the cracks on the surface.
In the past three years, there has been an increase in SFO’s runways repairs, most of which are due to “alligator cracks” or linear surface cracking. Several of these are emergencies, which means the airport maintenance team did not anticipate the damage and that it was critical enough to demand immediate attention.
SFO tries to remedy this problem by shutting down several runways and making total repairs. The regular maintenance program includes concrete leveling and repaving to increase the level of the runways to the waterline. The airport is also planning a long-term solution, which is to build seawalls that can mitigate the rising sea level and sinking land.
Uneven runways and bumpy rides
Another airport dealing with runway problems is the Columbia Regional Airport. The city of Columbia canceled American Airlines and United Airlines flights recently and closed down the second runway to fix the bump that pilots have been complaining about.
The “crown” or dip is located on the intersection of two runways. The lengthened runway meant that planes taxi along this at a higher speed, and the crown affects the smoothness of the cruise. Contractors fixed the dip by leveling the edges and repaving that portion of the runway.
Contrary to what many believe, many, if not all, runways are not perfectly smooth. This is why taxiing is usually bumpy. Runway humps develop for various reasons.
First, it’s almost impossible to perfectly level something that is as long as a runway. Second, the different elevation levels of the runway affect the plane’s acceleration, landing, and take off. Because of this, the slope is included in calculating the optimal take-off and landing points. If the pilot is aware of a runway’s humps, he or she can use these to more softly land the plane or more smoothly make the ascent. But miscalculating the touchdown point can cause rough landings.
Although there are valid reasons for the imperfect structure of runways, airport management and state officials must ensure that this does not become a hazard for passengers. With the growing number of flyers each day, it’s their duty to ensure the safety of all of these people.