Aeronautical Information Manual (AIM), page 422

Index   421 -- Page 422 -- 423

discretionary. The decision will depend on the
circumstances of the individual incident.

6-2-4. Emergency Locator Transmitter


a. General.

1. ELTs are required for most General Aviation
14 CFR SECTION 91.207.

2. ELTs of various types were developed as a
means of locating downed aircraft. These electronic,
battery operated transmitters operate on one of three
frequencies. These operating frequencies are
121.5 MHz, 243.0 MHz, and the newer 406 MHz.
ELTs operating on 121.5 MHz and 243.0 MHz are
analog devices. The newer 406 MHz ELT is a digital
transmitter that can be encoded with the owner's
contact information or aircraft data. The latest
406 MHz ELT models can also be encoded with the
aircraft's position data which can help SAR forces
locate the aircraft much more quickly after a crash.
The 406 MHz ELTs also transmits a stronger signal
when activated than the older 121.5 MHz ELTs.
(a) The Federal Communications Commis-
sion (FCC) requires 406 MHz ELTs be registered
with the National Oceanic and Atmospheric
Administration (NOAA) as outlined in the ELTs
documentation. The FAA's 406 MHz ELT Technical
Standard Order (TSO) TSO-C126 also requires that
each 406 MHz ELT be registered with NOAA. The
reason is NOAA maintains the owner registration
database for U.S. registered 406 MHz alerting
devices, which includes ELTs. NOAA also operates
the United States' portion of the Cospas-Sarsat
satellite distress alerting system designed to detect
activated ELTs and other distress alerting devices.
(b) In the event that a properly registered
406 MHz ELT activates, the Cospas-Sarsat satellite
system can decode the owner's information and
provide that data to the appropriate search and
rescue (SAR) center. In the United States, NOAA
provides the alert data to the appropriate U.S. Air
Force Rescue Coordination Center (RCC) or U.S.
Coast Guard Rescue Coordination Center. That RCC
can then telephone or contact the owner to verify the
status of the aircraft. If the aircraft is safely secured
in a hangar, a costly ground or airborne search is

avoided. In the case of an inadvertent 406 MHz ELT
activation, the owner can deactivate the 406 MHz
ELT. If the 406 MHz ELT equipped aircraft is being
flown, the RCC can quickly activate a search.

406 MHz ELTs permit the Cospas-Sarsat satellite

system to narrow the search area to a more confined
area compared to that of a 121.5 MHz or 243.0 MHz
ELT. 406 MHz ELTs also include a low-power
121.5 MHz homing transmitter to aid searchers in
finding the aircraft in the terminal search phase.

(c) Each analog ELT emits a distinctive
downward swept audio tone on 121.5 MHz and
243.0 MHz.

(d) If "armed" and when subject to crash-
generated forces, ELTs are designed to automatically
activate and continuously emit their respective
signals, analog or digital. The transmitters will
operate continuously for at least 48 hours over a wide
temperature range. A properly installed, maintained,
and functioning ELT can expedite search and rescue
operations and save lives if it survives the crash and
is activated.
(e) Pilots and their passengers should know
how to activate the aircraft's ELT if manual activation
is required. They should also be able to verify the
aircraft's ELT is functioning and transmitting an alert
after a crash or manual activation.
(f) Because of the large number of 121.5 MHz
ELT false alerts and the lack of a quick means of
verifying the actual status of an activated 121.5 MHz
or 243.0 MHz analog ELT through an owner
registration database, U.S. SAR forces do not
respond as quickly to initial 121.5/243.0 MHz ELT
alerts as the SAR forces do to 406 MHz ELT alerts.
Compared to the almost instantaneous detection of a
406 MHz ELT, SAR forces' normal practice is to wait
for either a confirmation of a 121.5/243.0 MHz alert
by additional satellite passes or through confirmation
of an overdue aircraft or similar notification. In some
cases, this confirmation process can take hours. SAR
forces can initiate a response to 406 MHz alerts in
minutes compared to the potential delay of hours for
a 121.5/243.0 MHz ELT.
3. The Cospas-Sarsat system has announced the
termination of satellite monitoring and reception of
the 121.5 MHz and 243.0 MHz frequencies in 2009.
The Cospas-Sarsat system will continue to monitor
the 406 MHz frequency. What this means for pilots is
that after the termination date, those aircraft with only

6-2-2 Emergency Services Available to Pilots

Page 422 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   421 -- Page 422 -- 423