ARTEX PRODUCTS / ACR ELECTRONICS, INC
DESCRIPTION, OPERATION, INSTALLATION AND MAINTENANCE MANUAL
B406-4 (453-5004)
Page 17 of 70
25-62-03
DESCRIPTION AND OPERATION
TASK 25-62-03-870-801
1.
Description
SUBTASK 25-62-03-870-001
A.
Functional Overview
1)
The ELT automatically activates during a crash and transmits the standard sweep tone on 121.5 and
243.0 MHz. Approximately every 50 seconds, for up to 520 milliseconds (long message protocol), the
406 MHz transmitter turns on. During that time, an encoded digital message is sent to the
COSPAS-SARSAT Search and Rescue (SAR) satellite system.
2)
The information contained in the message includes:
a)
Serial number assigned to the ELT by the beacon manufacturer or the national beacon registration
authority, or
b)
Aircraft identification or registration number, and
c)
Country of registration and country code; plus
d)
Position coordinates, when coupled with an ELT/NAV Interface -B (453-6501). Refer to the ELT/NAV
Interface -B Description, Operation, Installation and Maintenance Manual (570-6501) for a detailed
discussion of the interaction between the ELT, ELT/NAV Interface -B, and aircraft navigation
system.
3)
The 406 MHz transmitter will operate for 24 hours and then shuts down automatically. The 121.5/243.0
transmitter will continue to operate until the batteries are exhausted, which is at least 50 hours.
4)
The 406 MHz transmitter produces a much more accurate position, typically 3 kilometers as compared
with 15 to 20 kilometers for 121.5/243.0 MHz transmitters. When coupled to the aircraft navigation
system via the ELT/NAV Interface -B, the accuracy improves to approximately 100 meters.
5)
The ELT transmits a digital message that allows search and rescue authorities to contact the
owner/operator of the aircraft through information contained in a database. Information contained in
the database includes:
a)
Type of aircraft and aircraft registration number,
b)
Owner address and telephone number, and
c)
Alternate emergency contact.
6)
After the ELT is activated and the 406 MHz signal is detected by the SAR satellite system and a position
is calculated, the 121.5/243.0 MHz transmissions are used to home in on the crash site.
NOTE:
Effective February 1, 2009, COSPAS-SARSAT has terminated satellite processing of distress
signals from 121.5 and 243.0 MHz beacons.
7)
Aircraft communications transceivers are not capable of receiving 406 MHz transmissions; therefore, the
only methods of monitoring the ELT are:
a)
The cockpit remote switch panel light,
b)
The buzzer, or
c)
121.5/243.0 MHz transmissions, which can be monitored using the aircraft communications
transceiver or an AM radio tuned to 121.5 MHz.
