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Discrete Emergency Frequency

AIM ¶ 6-5-1 — Discrete Emergency Frequency

AIM 6-5-1 explains the Discrete Emergency Frequency (DEF) used by ATC, ARFF, and emergency aircraft. Study guide for pilot oral exams and checkrides.

In Plain English

AIM 6-5-1 describes how an aircraft in an emergency can talk directly to the people who can help on the ground. When an emergency happens at a towered airport, Air Traffic Control (ATC) picks a frequency from the tower's normal operating frequencies and assigns it as the Discrete Emergency Frequency (DEF). This single frequency lets the:

  • Flight crew of the emergency aircraft,
  • Aircraft Rescue and Fire Fighting Incident Commander (ARFF IC), and
  • Airport Traffic Control Tower (ATCT)

all talk on one common channel — eliminating relays and saving critical time.

If the airport has no tower, or the tower is closed, the crew can still reach ARFF (when ARFF service exists) by using either:

  • The Common Traffic Advisory Frequency (CTAF) published for that airport, or
  • The civil emergency frequency 121.5 MHz.

Knowing the DEF concept matters operationally because in a real emergency — fire, gear failure, medical — coordinated communication between the cockpit and rescue crews directly affects how quickly responders meet you on rollout.

AIM Source Text
FAA AIM ¶ 6-5-1
6-5-1. 6-5-1. Discrete Emergency Frequency 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.
Oral Exam Questions a DPE Might Ask
Q1What is a Discrete Emergency Frequency (DEF), and who uses it?
Per AIM 6-5-1, the DEF is an aeronautical frequency designated by ATC from the tower's operational frequencies that allows direct contact between the emergency aircraft flight crew, the Aircraft Rescue and Fire Fighting Incident Commander (ARFF IC), and the Airport Traffic Control Tower (ATCT).
Q2Who designates the Discrete Emergency Frequency?
Per AIM 6-5-1, ATC designates the DEF, selecting it from the operational frequencies already assigned to that ATC facility.
Q3If you have an emergency at a non-towered airport, or the tower is closed, what frequencies can you use to contact ARFF?
Per AIM 6-5-1, if ARFF service is provided you can contact the ARFF Incident Commander on the airport's published Common Traffic Advisory Frequency (CTAF) or on the civil emergency frequency 121.5 MHz.
Related Paragraphs in AIM Chapter 6
6-5-2
ARFF Radio Call Signs
6-5-3
ARFF Emergency Hand Signals
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AIM 6-5-1 — Discrete Emergency Frequency (DEF)