As the government shutdown continues for over a month, many airports have reported low staffing among Transportation Security Administration (TSA) officers and air traffic controllers. At the beginning of the month, Houston’s George Bush Intercontinental Airport was forced to close half of its security checkpoints, generating lines of over two hours for passengers to access the checkpoint. 

In the midst of what many passengers are calling “travel chaos,” the security checkpoints at San Francisco International Airport (SFO) remain running at full capacity and speed, thanks to a little-known reason that has kept them unaffected.

SFO is one of only 20 airports in the U.S. that participate in the TSA’s Screening Partnership Program (SPP), which contracts and allows private companies to run security screening at commercial airports. Today, SFO is the largest airport in the program, which mostly covers smaller regional airports like Tupelo Regional Airport (TUP) in Mississippi and some medium-sized airports like Orlando Sanford International Airport (SFB) in Florida.

The Complete List of TSA's SPP Airports:

• Atlantic City International Airport
• Charles M. Schulz–Sonoma County Airport
• Dawson Community Airport
• Great Falls International Airport
• Glacier Park International Airport
• Greater Rochester International Airport
• Havre City-County Airport
• Kansas City International Airport
• L. M. Clayton Airport
• Orlando Sanford International Airport
• Portsmouth International Airport
• Punta Gorda Airport
• Roswell International Air Center
• San Francisco International Airport
• Sarasota-Bradenton International Airport
• Sidney-Richland Municipal Airport
• Sioux Falls Regional Airport
• Tupelo Regional Airport
• Wokal Field/Glasgow International Airport
• Yellowstone Airport

While the security officers at SFO may have uniforms that appear to be TSA, they actually work for Covenant Aviation Security, a major security company in the aviation industry. Covenant is one of 27 companies the TSA has approved for the SPP program. The company also provides regulatory security duties — not involving passenger or baggage screening — at other major airports such as Denver International Airport (DEN), Miami International Airport (MIA), and Salt Lake City International Airport (SLC).

This means that security screening operations remain predominantly unaffected, as screening officers are employed by a private company and continue to receive pay, unlike TSA officers, who are federal employees and have not received any pay since the government shutdown began on October 1. Although TSA officers are still required to work without pay, many have called out of work as they cannot afford to do so and have resorted to seeking other jobs.

Although SFO hasn’t been completely invulnerable to delays — its air traffic controllers are still staffed by the Federal Aviation Administration (FAA) — its security checkpoints remain running at full capacity.