Sunday, July 1, 2012

ELT transmitter Test


             Whenever the ELT is switched from “ON” to “ARM” a 406 MHz signal is transmitted, however, it is specially coded as a “Self-Test” signal that is ignored by the COSPAS-SARSAT satellites
                
       Always perform the tests within the first 5 minutes of the hour. Notify any nearby control tower of your intentions.
              Do not allow test duration to exceed 5 seconds. A false alarm may be generated.
        Any time the ELT is activated, it is transmitting a 121.5 MHz distress signal. After approximately 50 seconds, a “live” 406 MHz distress signal is transmitted and is considered valid by the satellite system.


Self-Test
• Tune a receiver (usually the aircraft radio) to 121.5 MHz. Turn the ELT aircraft panel switch “ON” for about 1 second, then back to the “ARM” position. The receiver should voice about 3 audio sweeps.
• At turn-off (back to ‘ARM’ state) the panel LED should present 1 pulse (buzzer will not sound for 1 pulse). If more are displayed, determine the problem from the list below.
1 Flash – Indicates that the system is operational and that no error conditions were found.
3 Flashes – Bad load detected. Detects open or short condition on the antenna output or cable. These problems can probably be fixed by the installer.
􀂃Check that the RF cable is connected and in good condition. Perform continuity check of center conductor and shield. Check for a shorted cable.
􀂃Check for intermittent connection in the RF cable.
􀂃If this error code persists there may be a problem with the antenna installation. This can be checked with a VSWR meter. Check the antenna for opens, shorts, resistive ground plane connection.

4 Flashes - Low power detected. Occurs if output power is below approximately 33 dBm (2 watts) for the 406 signal or 17 dBm (50 mW) for the 121.5 MHz output.
􀂃Check coax and connections
􀂃Check antenna installation
􀂃Check that the frequencies are within acceptable limits

5 Flashes – Indicates the ELT was not programmed, or is incorrectly programmed. Does not indicate erroneous or corrupted programmed data.
6 Flashes – Indicates the G-switch loop between pins 5 and 12 at the D-sub connector is not installed. ELT will not activate during a crash.
􀂃Check that the harness D-sub jumper is installed by verifying less than 1 ohm of resistance between pins 5 and 12.

7 Flashes – Indicates that the ELT battery has too much accumulated operation time (> 1hr, see below). Battery may still power ELT; however, it must be replaced to meet FAA specifications. May also indicate damage to the battery circuit.
Self-Test Schedule -Artex recommends that the ELT be tested every 1-2 months. Follow the steps outlined above.
NOTE: The self-test time is accumulated in a register on the battery pack. The register records activation time in 30 second increments so all activations will count as at least 30 seconds, even if the actual time is much less. Total allowable time is 60 minutes as determined by FAR 91.207 and RTCA DO-204. After this time has been accumulated a 7-flash error will be presented after the self-test. The battery must be replaced at this point for the ELT to remain in compliance. Always follow ELT testing requirements per local or national

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