SV1000T - stayed on when batt master off

[swatson999]

2 flights ago, at the end of the flight, I did the annual backup battery test as the reminder came up this month. One flight after that for about an hour, so it got all nice and charged up.

Today, during preflight, I flipped the Master on as usual, checked lights and pitot heat, looked at the SV after it booted to verify a few things like Hobbs time, etc. (for oil change intervals and so forth), then flipped the master off. But this time, instead of powering down as it has for 4 years, the SV stayed on with the little red bar that said "Ext Power Lost" or something like that...had to power it down using the button for PWR OFF.

Weird, says I. Let's try that again. Same thing. Hmmmm....

Go flying for about a half hour...on shutdown, it's back to acting normally after I shutdown and turn off the Master.

Any ideas?

 

[Raymo]

I wonder if it still detected oil pressure and thought the motor was running, in which case it should remain on and let you know that primary power was lost (master switch off).

 

[dynonsupport]

It likely thought you were flying, which happens if you have any airspeed. Was there a lot wind?

 

[swatson999]

To answer both questions...I sure hope there was no oil pressure, since the plane hadn't flow in 3 days, and nope (it was in the hangar, winds calm as can be).

I'll look at the log file when I download it to see what might be going on here...but nothing jumped out at me as being obviously wrong on the screen that I noticed.

 

[turbopilot]

I reported this behavior several years ago. It has not happened again until a few weeks ago. First time it happened I just turned off the avionics master switch, watched the count down timer start and walked away. Next day when powering up I got the back battery warning.

A few weeks ago when it happened again I was watching the display as the count down started. When the count down went to "0" the display remained on running on the backup battery. I had to apply power again then shut it down to get it to go dark.

 

[Dynon]

It also might think you're on the move if GPS lock were iffy, which can cause it to walk a bit and cause some of the behaviors to treat you like you're in-flight (where you definitely don't want a countdown)

 

[turbopilot]

It also might think you're on the move if GPS lock were iffy, which can cause it to walk a bit and cause some of the behaviors to treat you like you're in-flight (where you definitely don't want a countdown)

This is possible. Both times the aircraft was in the hangar with GPS locking and unlocking.

 

[swatson999]

That *might* be what it was, but we'll see what the log shows. FWIW, the countdown timer *never* started...it just went straight to "EXT POWER LOST", which stayed on the screen as it should, with the two options to select (stay on or power down) on the soft keys.

 

[swatson999]

Looking at the logs...IAS was around 17 kts, with some noise.

Dunno why...

 

[ChiefPilot]

Looking at the logs...IAS was around 17 kts, with some noise.

Dunno why...

Mine does this as well. Even after doing the zero airspeed calibration in a still-air hangar with the pitot cover on.

It started with the v15 update; it was fine before v14 for me.

 

[swatson999]

Oddly, it only did it *that* day, and hasn't done it before or since. Still, does indeed sound like some sort of software bug...perhaps the combined GPS/air data solution when GPS is unreliable? (Like inside of a hanger?)

 

[ChiefPilot]

Oddly, it only did it *that* day, and hasn't done it before or since.  Still, does indeed sound like some sort of software bug...perhaps the combined GPS/air data solution when GPS is unreliable?  (Like inside of a hanger?)

Interesting! Mine does it whenever the system has been off for some time - if the unit has already warmed up and was off for only a short time (i.e. fuel stop) the problem doesn't happen. GPS availability doesn't seem to have an impact one way or the other.

 

[swatson999]

OK, it did it again yesterday...in a closed hangar, so I got a warning (No ADS-B Out - GPS POS unavailable, or something like that).

Airspeed was showing 16 knots. Clearly, an algorithm is wrong somewhere...perhaps a branch that is using GPS data to cross-check airspeed?

 

[Dynon]

If you're seeing airspeed, you'll get the power on/off message instead of the countdown. This is by design. If you're seeing airspeed at rest, you should do the zero speed calibration, which should eliminate it (and if not, give our support team a call or email). Also note that there isn't any cross-feeding of GPS and IAS. They're completely independent.

 

[swatson999]

If you're seeing airspeed, you'll get the power on/off message instead of the countdown. This is by design. If you're seeing airspeed at rest, you should do the zero speed calibration, which should eliminate it (and if not, give our support team a call or email). Also note that there isn't any cross-feeding of GPS and IAS. They're completely independent.

I'll do that this weekend...just curious why it *suddenly* started doing this, after several years of never having seen this behavior.

If it keeps doing it, after the calibration, I'll give them a call. Thanks!

Steve

 

[swatson999]

Hmmm...3 more flights, plus several power on events in the hangar, and it hasn't done it again, despite NOT having done the zero airspeed calibration (because my airspeed is already, in fact, showing 0 when in the hangar).

*Something* in the system thinks, every so often, that it is seeing 15-20 knots of airspeed...but it's not consistent. I just has a pitot/static/XPDR test done back in February, and everything was nigh-on perfect. And it has been so for several years, except for these odd occasions.

I'm not terribly concerned with it being wrong on the ground, other than being annoying (and making me wonder what's going on), but I'd like to be assured somehow that this is not an algorithmic or systemic problem which can somehow manifest itself in flight. Erroneous airspeed indications have caused more than their share of accidents, and I don't intend to be a statistic myself, which is why I do think this bears more investigation by Dynon (since others have, apparently, seen the same thing).

 

[dynonsupport]

There is no bug here. Everything is operating 100% as expected.

Our logic for shutdown is simple. Airspeed not zero? Don't shutdown without user interaction.

SkyView's airspeed doesn't come alive until 20 knots, and then stays alive down to 15. Thus, you need to read 20 knots at some point to see the 15. We don't ever show speeds 0-15 knots because this would just be random noise given how small these pressures are, and we don't show 15-20 on the way up  in order to have some hysteresis on it coming on and off.

15 knots is .005 PSI. 20 knots is .01 PSI. 30 knots is .020 PSI. 33 knots is .025 PSI.

Our airspeed sensors work to 300+ knots, where the pressure is 2 PSI. So we need a sensor to work from .005 PSI with .001 PSI resolution up to 2 PSI.

This is why most airspeed gauges start at 30-40 knots. Dealing with the really low pressures is hard. The sensor only needs to drift 0.1% to lead to showing 15 knots at zero, but that same 0.1% drift is only 1 knot at 50 knots.

Sensors age, and they drift just a touch, so now your base pressure is 0.004 PSI (13 knots). They might be 0.002 PSI different at different temperatures (16 knots). A bit of wind hits the pitot and moves it from 0.006 PSI to 0.010 PSI (20 knots) and then goes away. The system reads 20 and activates airspeed and then goes back to 16, which leaves the airspeed up. But it's not the same temperature every day, and the same gust doesn't hit it each time so it doesn't always happen. Sometimes it just hovers between 13 and 16 knots and we never show it.

And none of this matters at speed because it's all irrelevant by 50 knots. But it does mean that over time, sometimes you will see airspeed when there is none. Which is why we have zero airspeed cal, and recommend you run it once a year (see our instructions for continued airworthiness on page 21-9 of the install manual).

 

[swatson999]

Cool, thanks...that *definitely* clears things up, and might very well explain it. I will, therefore, do the calibration tomorrow.

Thanks to Dynon support for a very cogent explanation, and for taking the time to edumucate me on this aspect of the system. Well done!

 

[turbopilot]

There is no bug here. Everything is operating 100% as expected.

Our logic for shutdown is simple. Airspeed not zero? Don't shutdown without user interaction.

Is this about IAS being sensed via the pitot tube or erronius GPS ground speed indicated in fringe conditions? Got the impression earlier you were indicating jumps in GPS ground speed in fringe situations could account for an aborted shutdown.

For my part both aborted power downs (leading to back up battery depletion) took place in my hangar with no significant air movement at the pitot tube. The GPS was jumping in and out of lock with the hangar door open.

 

[airguy]

Which is why we have zero airspeed cal, and recommend you run it once a year (see our instructions for continued airworthiness on page 21-9 of the install manual).

Aaahhhh - now that is an interesting little tidbit that I missed in the manual. I'm going to add a line to my annual condition inspection checklist to perform the zero-airspeed calibration now, thanks for the explanation!