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Old 05-29-2018, 03:43 PM
g3xpert's Avatar
g3xpert g3xpert is offline
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Location: Olathe, KS
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Originally Posted by nomocom View Post
My annunciation light is now hooked up and Iím seeing the same thing. It turns on long enough at startup to confirm the light works, then shuts off, before a valid position is acquired. Also, later when switching the transponder to mode A, that shorts the GDL the pressure altitude and should cause the light to turn on. It doesnít. I trust we can get a software update, if not a useful one, at least one that will turn it on for a few seconds randomly for the entertainment of passengers.
Hello Stan,

Whenever it makes sense, we like to suppress fault indications for things that are temporary and expected at every power-up.

At each power-up the GDL 82 inhibits the GPS data available fault for 2.5 minutes to allow the GPS time to acquire first fix. It the GPS still doesn't have a usable fix after 2.5 minutes, the fault indication is provided. If the GPS data becomes unavailable in flight, the fault indication comes on immediately.

Pilots typically only ever disable altitude reporting when requested by ATC with the pilot in the loop, so the decision was made to not show a fault indication for this rare and intentional action.

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Old 06-04-2018, 04:08 PM
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nomocom nomocom is offline
Join Date: Jun 2009
Location: Caldwell ID
Posts: 238
Default fault light

Thanks for the explanation Steve. I was chuckling- give the coders smart "black tape" to cover the annoyance! I get it. The visual load on the pilot is sometimes high. Why not suppress the light when it is unimportant. Light on or light off, I don't have a strong preference for either behavior, but I do have a preference for accurate manuals so I know what to expect.

On the other, the pressure altitude, IMO, if ATC asks me to shut of mode C, I'd rather see the light come on. Those of us opting for UAT will likely spend a good deal of time, 1200 anonymous. I'd prefer to have the light if my out has a problem. Consider that this UAT unit is targeted toward those who largely want to keep their existing transponder and blind encoder. We are talking old equipment in many cases. Blind encoders do fail and I've seen poor connections as well. Given the structure of Gillham code, when there is an error, it can translate to a wrong altitude that is off a great deal more likely than off a few hundred feet. As long as the team is building smart fault lights.... any thought to a compare statement between pressure altitude and GPS altitude? It would need to have lots of fudge, extreme example, IIRC about 4,500 feet pressure altitude at sea level during record low pressures (hurricane). GPS and pressure altitude seldom agree, but with all the smarts at Garmin.....

In the big picture, probably not a big deal to ignore pressure altitude faults. Most users will probably have some kind of portable IN (that is how I saw the behavior that was contrary to the manual). So if the fault light doesn't come on, perhaps it will be noticed in the "own ship" values. But also big picture, why add a fault light if you don't allow the code to trigger it per the manual- anytime the GDL is not broadcasting FAA required information?

Bottom line for me, whatever Garmin does with the fault code, put it in the manual so we know what to expect.
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Old 06-05-2018, 05:23 AM
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snopercod snopercod is offline
Join Date: Aug 2016
Location: Asheville, NC
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Originally Posted by nomocom View Post
... I've seen poor connections as well. Given the structure of Gillham code, when there is an error, it can translate to a wrong altitude that is off a great deal more likely than off a few hundred feet.
I had that happen recently. The altitude being sent was off by 2,000' IIRC. Turned out to be a loose connection to the encoder.

Interesting trivia regarding the anonymous mode and FlightAware: If you set the switch to "anonymous" before startup, and begin your flight with a code - departing a Class C for example - when you change to 1200 mid-flight, Flight Aware still knows your tail number and displays your entire flight. I haven't tried it the other way around yet. When your entire flight is flown squawking 1200, FlightAware doesn't track you.
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