Artex ELT345 questions

FireMedic_2009 said:

I recently bought the ELT345.

On pg 17 I read the ELT345 has an internal gps and is accurate up to 3km or if it receives aircraft navigation gps it is accurate to 100 meters. Can the unit receive aircraft navigation? On the installation I don't remember seeing any connections to the aircraft gps.

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The reference to 3km accuracy is the basic system accuracy of the 406MHz system. Of course a big part of that system is the fleet of satellites which monitor the 406 signal. The accuracy to which these satellites can triangulate the position of a 406MHz transmitter is about 3km. GPS is NOT used in this triangulation process.

The ELT can receive GPS position data from an on-board GPS receiver via an RS232 serial input. Note: with this particular ELT one has to be careful when purchasing the unit to ensure it is programmed to receive GPS data in the same format as the output format of the GPS receiver to which you want it connected by an RS232 serial data link. The ELT will support multiple different GPS position data streams, but is unable to differentiate between them thus it must be programmed at the factory for the exact data type which you have chosen to feed it.
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On page 17 it states the 406 transmitter will operate for 24 hrs before shutting down and the 121.5 will operate for at least 50 hrs. Why would the 406 transmitter need to output more than a few transmissions if it contains gps coordinates? It's not like the 121.5 where you have to home in on the signal.

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The 406 needs to output more than a few bursts for a LOT of reasons. The principle reason is that position triangulation of the transmitter often requires multiple satellite passes. Those passes don't happen in a matter of seconds or minutes but sometimes (depending on your geographic location) it may take hours. Now add to the equation the vagaries of the crash location itself - maybe the airplane is on its side, under coniferous trees that suck up signal, etc etc etc. Believe me, you want that 406MHz signal blasting out for some time in order to give you maximum probability of overcoming all the odds that might be stacked against you.

Note also that the 121.5MHz "warble" signal is transmitted by the ELT any time it's not sending out a blast of 406MHz transmission. Simply put, the 406MHz signal will be sent out 50 seconds after activation, either by a crash or by manual activation. Once that first burst of 406 signal is sent (it's short, less than a second) the 121.5 warble will be transmitted for the next 50 seconds or so before the next 406 burst is transmitted. This goes on for 24 hours, after which the 406 bursts are stopped and the 121.5 goes on until battery exhaustion.
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This leads to another question. If the 406 transmission will operate for 24 hrs why would you need to replace the battery after an hour of use, pg27???

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The hour of use requirement comes from the fact that one might have inadvertently activated the ELT but only for a "few minutes". Add to that the activation time that comes from performing self-tests. When all that "on" time adds up to an hour the batteries are no longer assured of providing the full endurance if a crash should happen near the end of their calendar life. Don't question the rule - it's there for your safety - just replace the battery pack.
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Testing of the unit must be performed annually or every 100 inspection. I fly over 100 hrs/yr. Do the 100 hr inspections on the ELT apply to us or only for aircraft rentals and charters?

Thanks,
Daren

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