AIM Text
- Direct contact between an emergency aircraft flight crew, Aircraft Rescue and Fire Fighting Incident Commander (ARFF IC), and the Airport Traffic Control Tower (ATCT), is possible on an aeronautical radio frequency (Discrete Emergency Frequency [DEF]), designated by Air Traffic Control (ATC) from the operational frequencies assigned to that facility.
- Emergency aircraft at airports without an ATCT, (or when the ATCT is closed), may contact the ARFF IC (if ARFF service is provided), on the Common Traffic Advisory Frequency (CTAF) published for the airport or the civil emergency frequency 121.5 MHz.
Source: FAA Aeronautical Information Manual · current edition · paragraph 6-5-1.
The short answer
This AIM section is FAA advisory guidance describing the Discrete Emergency Frequency (DEF) — an aeronautical frequency ATC designates from a facility’s operational frequencies so an emergency aircraft flight crew, the ARFF Incident Commander, and the Airport Traffic Control Tower can communicate directly. It also covers fallback to CTAF or the civil emergency frequency 121.5 MHz at non-towered or closed-tower airports, supporting emergency operations under 14 CFR 91.3.
Research Notes
Common Questions
What is the Discrete Emergency Frequency (DEF)?
Per this advisory section, the DEF is an aeronautical radio frequency designated by Air Traffic Control from the operational frequencies assigned to that facility. It enables direct contact between an emergency aircraft flight crew, the Aircraft Rescue and Fire Fighting Incident Commander (ARFF IC), and the Airport Traffic Control Tower (ATCT).
How do I reach ARFF at a non-towered airport or when the tower is closed?
The section states that emergency aircraft at airports without an ATCT, or when the ATCT is closed, may contact the ARFF IC (if ARFF service is provided) on the Common Traffic Advisory Frequency (CTAF) published for the airport, or on the civil emergency frequency 121.5 MHz.
Who assigns the DEF?
Air Traffic Control designates the DEF from the operational frequencies already assigned to that facility, so the flight crew, ARFF IC, and ATCT share a common channel during the emergency.