ELT SYSTEM – GENERAL
The purpose of the Emergency Locator Transmitter (ELT) is to help locating
the aircraft after a crash or an emergency landing.
The ELT automatically activates following a crash because of the internal gswitch
and transmits the standard tone on VHF and UHF guard frequencies
(121.5 MHz and 243.0 MHz) and coded information to the SARSAT system
(406.025 MHz).
The 406.025 MHz transmitter sends an encoded digital message containing
aircraft identity (ELT serial number) and the last aircraft position as received
from the FMS.
ELT SYSTEM – MAIN COMPONENTS
The ELT main components are:
• the ELT unit
• the ELT/NAV Interface Unit which provides the ELT with the FMS
position data
• the ELT control panel
• the buzzer which operates whenever the ELT is activated
• the ELT antenna, which has two connectors: one for 121.5/243.0 MHz
and one for 406.025 MHz
ELT SYSTEM – PRINCIPLE OF OPERATION
Following an automatic or manual activation, the ELT starts immediately
transmitting on both guard frequencies and after 50 seconds it starts
transmitting also on 406.025 MHz.
Once activated, the 121.5 MHz and 243.0 MHz transmitter will continue to
operate until the battery power is exhausted, which will typically be longer
than 48 hours, whilst the 406.025 MHz transmitter will operate for 24 hours
before shutting down automatically.
An aural (buzzer) and a visual (red LED) monitor is provided to alert the crew
when the ELT is transmitting.
For normal operation the switch on the ELT control panel must be in ARM.