Ed_Wischmeyer
Well Known Member
Ever since my RV-9A went all glass, I've struggled to learn all the system failure modes, a task much more involved than in the days of steam gauges and manual calculations.
One level of analysis is what happens if a single component fails. In my airplane, if the ADHRS fails, the G5 still provides basic air data to the screens and the autopilot, but I lose AOA, and lose OAT, which means losing true air speed and winds, and I lose magnetic heading, so everything reverts to GPS track, that last being not that big a deal.
Similarly, if I lose the CANbus, I lose pitch servo and elevator trim speed adjustment, the flight director and autopilot lose access to the IFR navigator and are restricted to the VFR only GPS located in the display screens, and I can display lateral GPS and VOR/ILS guidance only on the IFR navigator with no vertical guidance available. I think.
These failures are the kind that an examiner could, IMHO, reasonably ask on an Instrument Rating checkride, or that a conscientious CFI could ask on a Flight Review.
But there's more. Suppose on the ADHRS, the barometric pressure sensor fails. Sure, the air data will all be compromised, but will the system self-monitor only shut off those outputs, or will it fail the entire system, including the attitude indicator? Will the gyros get rate aiding over the CANbus and keep working? Documentation doesn't say, and I have no idea. And there are other partial failure scenarios to wonder about.
On the flight home from Oshkosh, the IFR GTN650 gave me a Cooling Fan Failure warning. At the next gas stop, I called Garmin and they told me that the cooling fan only cooled the display, but that the unit would keep working. I set the backlight to minimum, not knowing any better and hoping it would help.
Of course, if the display fails, you don't know what frequencies you're set to and can't program the flight plan. I called ATC before takeoff -- I would be going through the St. Louis Class B, other things being equal -- and described a contingency plan that they agreed to.
On the next leg, I got a Display Overheat warning. I didn't realize at the time that I could still tune the comm radio and the VOR/ILS from the G3X displays.
But I didn't realize until much later that if the display failed, I couldn't switch the navigator's output from GPS to VOR/ILS. (I want to add an external switch to do this, but until this flight, I'd not considered its use in a failure mode).
Bottom line is that there's lots to consider!
My IFR fallback is that my CFII once had me fly a non-precision approach using only the G5 standby flight display and a handhelp Garmin aera 660, simulating a total electrical failure. Sort of. I cheated and used the electric trim.
Lots to think about and wonder about, and this is without considering multiple failures (aside from total electrical failure). And with most systems being custom installations...
One level of analysis is what happens if a single component fails. In my airplane, if the ADHRS fails, the G5 still provides basic air data to the screens and the autopilot, but I lose AOA, and lose OAT, which means losing true air speed and winds, and I lose magnetic heading, so everything reverts to GPS track, that last being not that big a deal.
Similarly, if I lose the CANbus, I lose pitch servo and elevator trim speed adjustment, the flight director and autopilot lose access to the IFR navigator and are restricted to the VFR only GPS located in the display screens, and I can display lateral GPS and VOR/ILS guidance only on the IFR navigator with no vertical guidance available. I think.
These failures are the kind that an examiner could, IMHO, reasonably ask on an Instrument Rating checkride, or that a conscientious CFI could ask on a Flight Review.
But there's more. Suppose on the ADHRS, the barometric pressure sensor fails. Sure, the air data will all be compromised, but will the system self-monitor only shut off those outputs, or will it fail the entire system, including the attitude indicator? Will the gyros get rate aiding over the CANbus and keep working? Documentation doesn't say, and I have no idea. And there are other partial failure scenarios to wonder about.
On the flight home from Oshkosh, the IFR GTN650 gave me a Cooling Fan Failure warning. At the next gas stop, I called Garmin and they told me that the cooling fan only cooled the display, but that the unit would keep working. I set the backlight to minimum, not knowing any better and hoping it would help.
Of course, if the display fails, you don't know what frequencies you're set to and can't program the flight plan. I called ATC before takeoff -- I would be going through the St. Louis Class B, other things being equal -- and described a contingency plan that they agreed to.
On the next leg, I got a Display Overheat warning. I didn't realize at the time that I could still tune the comm radio and the VOR/ILS from the G3X displays.
But I didn't realize until much later that if the display failed, I couldn't switch the navigator's output from GPS to VOR/ILS. (I want to add an external switch to do this, but until this flight, I'd not considered its use in a failure mode).
Bottom line is that there's lots to consider!
My IFR fallback is that my CFII once had me fly a non-precision approach using only the G5 standby flight display and a handhelp Garmin aera 660, simulating a total electrical failure. Sort of. I cheated and used the electric trim.
Lots to think about and wonder about, and this is without considering multiple failures (aside from total electrical failure). And with most systems being custom installations...
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