In most pressurized aircraft, the air you breathe is sucked in from the engines and introduced through vents all over the cabin. To maintain air pressure, some air leaves the cabin through a baffled outflow valve usually located near the cockpit.

This outflow valve is on the opposite end of the plane from the toe of the sock, and would therefore act in opposition, airflow-wise, to the air pump protecting the crew from disease. In the modified corporate jet that flies the ABCS, Phoenix Air sealed the outflow valve up front and installed a new one in an unused luggage compartment in the rear, running the plane’s airflow backward, through the gradient of the sock, and out CDC-designed HEPA filters to the sky.

If the ABCS is a rubber raincoat, the CBCS is a submarine, down to 400-pound airtight doors that separate the clean, gray, and biohazard sections. The size of a semi-truck trailer, it has its own power and medical oxygen, and can be loaded onto a Boeing B-747/400 and shipped out of Atlanta’s Hartsfield-Jackson International Airport within 24 hours. The CBCS solves a major problem Phoenix Air faced during the 2014 epidemic, which was that they could only pick up one patient at a time, every three days, potentially dooming anyone left behind to wait for a later flight. The CBCS can transport four extremely sick, extremely contagious people, along with six medical staff, simultaneously.