Problem with Misc. Field displayed on my GI275/HSI

[NicoN]

GI275 has an option to display a "Misc. Field" in the display of a PFD and also on the HSI.

one option is to display wind/velocity in different versions

I configured the HSI to display wind direction and velocity. Therefore a little block appears on the display with "360/--"; sounds fine. The aircraft is on ground, so no GPS-Speed or track and also no airspeed.

 

But, while in the air, it did not display the wanted information - still "360/--".

Then - while - flying, i configured the same setting again, and voila, now it displayed a value (no clue if correct).

 

on my next flight - same problem again, information is displayed but non-sense. And again, problem can be solved by applying the setting again.

 

Any ideas ? is this a known problem? i did not see that this is addressed by a higher firmware (we have 2.62)

[Vance Harral]

Do you have a digital OAT probe system connected to your Garmin avionics, that along with pressure altitude allows the computation of true airspeed?

Calculation of winds aloft requires knowing true airspeed in addition to GPS-derived ground speed.  No digitally connected OAT probe, no winds aloft data.

[flyboy0681]

3 hours ago, Vance Harral said:

Do you have a digital OAT probe system connected to your Garmin avionics, that along with pressure altitude allows the computation of true airspeed?

Calculation of winds aloft requires knowing true airspeed in addition to GPS-derived ground speed.  No digitally connected OAT probe, no winds aloft data.

I was about to reply with the same answer.

[NicoN]

Sorry, my posting was not precise. English is not my native language.

And yes - we have OAT, we see as calculated TAS on PFD; that works

The Misc. Field on the PFD can display winds aloft in different flavors, such as  Headwind/crosswind, windspeed and a little arrow for direction and also windspeed and driection in degress. All work fine on the PFD

Same can be configured on the HSI and this time the indication of valid information does not start automatically, but only afetr appling the setting again.

then I see the information I want.

On top, the setting seems to be volatile; with the next flight  the same problem arises - definitely  not a real problem but annoying.

 

[NicoN]

Video to demonstrate th eproblem

As you can see, I have winds aloft indication on the PFD and also TAS.

 

The problem  for the HSI is also shown

 

[Vance Harral]

OK, the video makes it easier to understand your question.

I'm not a GI-275 expert, but based on general principles I have two guesses.  One is that it's a software issue as you speculate: either a bug, or a config setting that is so esoteric and convoluted it may as well be a bug.  That seems the most likely cause, but you'd have to check with Garmin on that.

My wild conspiracy theory involves the inputs an air data computer needs to compute winds aloft.  Those are pitot pressure, static pressure, OAT, ground track, and ground velocity.  To the best of my knowledge, each GI-275 receives these inputs "directly", meaning the HSI does not rely on the PFD to transmit them, but rather that it has it's own independent inputs (albeit ones which may be connected in parallel to the PFD).  In the GI-275, the pitot and static pressure inputs come from actual pitot and static lines connected to the instrument.  Everything else is electronic wiring.  It's somewhat unlikely the electronic wiring of your HSI is compromised, as that's "all or nothing" data that would likely cause other problems you probably would have noticed.  But I'm wondering if it's possible the pitot and/or static lines are slightly loose or slightly clogged, such that the air pressure data received by your HSI is erratic in a way that might cause certain air data functions to "go offline", particularly at low speed (i.e. on the ground).  This would require a situation where the pressure lines are good enough not to generate red Xs, but not good enough for whatever code computes winds aloft.  Seems very unlikely, but an easy experiment is to pull the breaker on the PFD in flight (on a good VFR day, obviously), and let the HSI revert to being a PFD.  Then you can see if the airspeed an altitude on that unit are erratic in any way.  If so, you might check the pitot and static connections to it.

[NicoN]

Thank you!

I am also of the opinion that it is not a general problem.

1. HSI can work as a PFD, I checked the auto-revert feature a couple of months ago - IAS and altitude are the same and headings is also fine

2. you can see that the msic. Field CAN indicate the winds aloft. Nevertheless there are rumours that in general the winds aloft calculation  might confuse left and right

 

Garmin was not interested in my video but recommended to find a solution with my authorized Garmin dealer. To be honest: my "authorized Garmin dealer" was not able to complete the calibration of the GMU11. They did not even have a secret contact to a Garmin guru to find the solution

 

We are definitely not on the latest firmware (we have 2.62). Wasn't there something that the latest firmware  makes my analog NAV2 (KX155) useless?

 

I was hoping that someone says "this problem is solved with FW xyz" or a  sophisticated config value

[Vance Harral]

Sounds like a firmware update is the next thing to try if you're not on the latest version.  Can't offer you much more in the way of suggestions - we're just lowly G5 consumers, I haven't tried to follow the GI-275 firmware versions.

I'm not in the avionics business, but I am in the electronics business, and I have at least some sympathy for Garmin wanting most of their service business to work through shops with which they have an established relationship.  Things do tend to go better that way for a collection of reasons.  But anyone in this sort of business also understands that granting "authorized dealer" status doesn't make that specific shop a good resource vs. a skilled DIYer.  Sorry you had a a mediocre experience with your last Garmin shop, but it's not particularly surprising.  I recently had a bad experience with a "Mooney Service Center", so I feel your frustration.