One thing that didn't go down during the FAA outage: AM radio. Pilots still use AM on the 108-137 MHz VHF aircraft band to communicate with each other and control towers. Unlike digital, it allows very weak signals to be heard, and unlike FM's capture effect, if two users transmit at the same time on the same frequency, listeners will hear a combination of both, allowing a distress call or alert from the control tower to come through. https://en.wikipedia.org/wiki/Airband