Tom-D
Taxi to Parking
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Tom-D
Battery internal.
What's this term mean?
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Tom-D
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It is installed and working properly with pin 9 wired for future use if needed.
Power in for what? I believe that this ELT is battery powered. The page in question shows input for a GPS, a buzzer which indicates the ELT is transmitting, and (I think) a switch which allows a pilot to turn it off in case of a false alarm.
arnoha
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Right...I had asked about external GPS in another thread related to this. (There are now three threads on @Tom-D installing a 406MHz ELT.) Was confused as to how that worked...if you crashed, odds are good you would have wrecked your GPS. Therefore, there's a high likelihood that there is no GPS source at the time of the crash. I was told in the other thread that the 406 MHz ELTs are taking the locations all the time and have external power to be able to do this. They send the last known location.
But now it appears there's no power. Which means the GPS unit must be operating at the time the crash sets off the G-switch to get a GPS location? There's no way the ELT can run years on the battery doing constant updates of the position. I'm definitely missing something about how 406MHz ELTs work when they don't have built-in GPS.
Tom-D
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It has a battery that is good for 10 years built into the case of the ELT.
The 406 feature sends out a signal that says the aircraft registered to the ELT has crashed. That's all. then emits a 121.5 wail just like the old ELTs did.
I think Tom's reply refers to his installation described in this thread. The 406 will continue to send out data since they can still use Doppler and other means to get a location from the satellites. The data burst is sent periodically. As Tom mentioned, the 121.5 MHz signal is also transmitted.
There are several types of 406 MHz ELT systems. Some, like this one (https://www.dallasavionics.com/artex/elt3000.pdf ) work as you describe- they use external power and use the last known location from the aircraft GPS. There are systems with the GPS built-in to the unit and only use the internal battery. Based on my experience with GPS, I suspect these systems need time to receive the GPS signal, obtain ephemeris data, and calculate their position- this can take several minutes- look up "GPS cold start", but the advantage is that the position is accurate. The final installation type is as Tom has performed, with no GPS; the 406 MHz signal is still transmitted as described earlier. The 406 MHz signal is received by the satellites and is still used to generate an approximate position as mentioned earlier.
http://www.cospas-sarsat.int/en/beacon-ownership/what-happens-when-i-activate-my-beacon
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brcase
En-Route
Approved? Is the wrong question. The correct question is, is it prohibited?
arnoha
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Yeah, I understand how GPS and WAAS work, at least in concept, and how the position solution is derived. I get that a fully non-GPS 406 works roughly like a 121.5 ELT. I get the one with an on-board GPS works as you describe, needing to start the position solution from scratch. And I understand the one you linked, that takes aircraft power and is continuously recording the last position from the RS-232 port.
It's the diagram for the one that @Tom-D installed that you posted that I don't get. It has an RS-232 Rx port, but no ship's power. It can't be doing as the one you linked does, always monitoring the RS-232 port. RS-232 is quite a high power consumption serial standard. There's no way you're running that off a battery for years. So they're either doing something insanely clever (using the Rx port for power somehow?) or they're only taking a position from the GPS after being activated, which seems less than ideal.
@Cap'n Jack , get what I'm asking? When and how frequently is the GPS position taken from the GPS source with the ARTEX 345? The mode of operation that I would imagine it using given the wiring doesn't make sense from a safety perspective. So, a bit of mental dissonance I'm trying to resolve.
The bolded text is what they are doing. It is less than ideal. It doesn't monitor the serial input until activated. Keep in mind that if you know you are going down, you can manually turn the system on (with the "external-on", pin 14 in the diagram) before the crash and it can send out GPS signals as long as it receives data from the external GPS. NMEA data is updated at least once a second.
arnoha
Cleared for Takeoff
Thanks for the explanation. Very useful. Means that there are two different styles of grabbing an external GPS position in 406 ELTs and I know which one I'd want. This one isn't it. Will avoid the ARTEX 345 when I upgrade to 406.