As air traffic controllers miss their first full paycheck, larger numbers of the workforce are calling in sick—forcing the Federal Aviation Administration (FAA) to slow the flow of traffic at some of the nation’s busiest airports.

Air traffic controller staffing shortages worsened over the weekend as the nation’s government shutdown hit its fourth week, leading to delays and anxiety, and experts say it won’t get better until air traffic controllers get paid.

While the Federal Aviation Administration is facing an air traffic controller shortage, it’s testing a modern alternative to the traditional air traffic control system called a remote tower. The head of Johnston Regional Airport wants to be “first in flight” once this digital remote tower takes off.