What is the FAA’s Notice to Air Missions (NOTAM)?

Travelers wait in the terminal as an Alaska Airlines plane sits at a gate at Los Angeles International Airport in Los Angeles (Credit: Stefani Reynolds—AFP/Getty Images)

Thousands of flights across the U.S. were grounded Wednesday morning after the Federal Aviation Administration’s system that sends vital communications to pilots experienced an outage.

The FAA said in a statement that it was working to restore its Notice to Air Missions System, but until it was fully operational again, flights across the national airspace would be affected.