Hello folks,
I’d like to get your advice and opinion on this.
My aircraft is G1000 equipped, with a GRS77 Garmin AHRS.
A few months ago, I lost artificial horizon and heading on firm (not hard) touch down.
I checked the connectors to both PFD and MFD, and also to GRS77. No bent pin, no free movement, no dust or corrosion preventing contact. I used KONTAKT 60 cleaner.
The thing didn’t appear for a while, and then again yesterday, two times.
What is pretty clear is that the thing is related to the “shock” of landing. It is perfectly synchronous. The AHRS retrieves alignement within 30 seconds.
For what I have seen, it never happens if landing is perfect.
Also, it has never happened in flight, whatever were the turbulences.
The AHRS was installed in 2006, is 1520TT, and was never serviced.
Do you consider it is a failure mode for the AHRS which is dying ?
Or a bad contact thing somewhere ?
Do you think the GMU44 (magnetometer) should be investigated ?
Of course I can change the AHRS and see. But I prefer see, then change :-D
Thank you for your help.
PetitCessnaVoyageur wrote:
Do you think the GMU44 (magnetometer) should be investigated ?
We had that fail on our G500 and only the heading did disappear and the AHRS took longer to initially stabilize.
PetitCessnaVoyageur wrote:
Of course I can change the AHRS and see. But I prefer see, then change :-D
Change AHRS 1 with AHRS 2 ? :)
That way you will see if it is a cabling issue or not.
Sebastian_G wrote:
We had that fail on our G500 and only the heading did disappear and the AHRS took longer to initially stabilize.
This is what I thought too, so the GMU44 should not be faulty.
Actually, if GPS or heading missing, GRS initialization gets longer or never ends from what I read.
As the GMU44 connects to the GRS77, it is not surprising heading disappears when the problem occurs.
Could it be that the GRS77 looses power intermittently and reboots ?
arj1 wrote:
Change AHRS 1 with AHRS 2 ? :)
This is on Airbus Cirrus you have two AHRS :-D
PetitCessnaVoyageur wrote:
The AHRS retrieves alignement within 30 seconds.
This 30 sec timing makes it sound like a power issue with the GRS not a data connection issue. Does the G1000 also record bus voltage and AMPs?
Malibuflyer wrote:
This 30 sec timing makes it sound like a power issue with the GRS not a data connection issue. Does the G1000 also record bus voltage and AMPs?
Thank you for your input.
Well, it records Main and Emergency Bus Voltage and Main & STBY battery Amp, so it may be worth checking what happens, you’re right.
30sec is what it needs in any case, so it’s not different.
The question is: could there be something “loose” inside the GRS, causing the current drop after “shock” (and the box to reboot).
What is AMPs ?
I don’t know if it is relevant to your problem or not, but do you have the latest software?
My club also has a 2006 G1000 aircraft which lost attitude in 2015 during IFR at FL80 (in and out of clouds…). The AHRS restarted and we got attitude back after about a minute. A talk with our local avionics shop revealed that there was a software update to fix precisely this issue. The work cost would even have been covered by Cessna/Garmin if the update had been installed as it was released. Apparently our then CAMO didn’t care about avionics-related SB’s…
PetitCessnaVoyageur wrote:
What is AMPs ?
Apparently not Aircraft Maintenance Programmes in this context. 
I would guess “amperes”, i.e. current. It would depend on the airframe what the G1000 records. On Cessna 172/182s it records battery (dis)charging current, not total current draw, as that’s the ammeter is set up on those aircraft – G1000 or not.
Airborne_Again wrote:
I would guess “amperes”, i.e. current.
YEs :-)
Airborne_Again wrote:
My club also has a 2006 G1000 aircraft which lost attitude in 2015 during IFR at FL80 (in and out of clouds…). The AHRS restarted and we got attitude back after about a minute. A talk with our local avionics shop revealed that there was a software update to fix precisely this issue. The work cost would even have been covered by Cessna/Garmin if the update had been installed as it was released. Apparently our then CAMO didn’t care about avionics-related SB’s…
This where you find the KAP140 a really interesting autopilot ;-)
I check my SB/AD records, and found what you may talk about: SB07-34-06
SB07_34_06_GRS77_MOD1_pdf
In my record, I noted I was not concerned, but there seems to be a discrepancy.
My GRS77 SN is 42000782 (then I should not be concerned) and aircraft SN is 18281767 (then I’m concerned).
I will check if Mod1 was applied, but this is an interesting path… Thank you AA.
PetitCessnaVoyageur wrote:
This where you find the KAP140 a really interesting autopilot ;-)
Indeed!
I check my SB/AD records, and found what you may talk about: SB07-34-06
SB07_34_06_GRS77_MOD1_pdf
That’s not the one as it is a hardware modification and ours was pure software update.
I found Cessna Service Newsletter SNL11-15 from 2011 (which includes Garmin Service Advisory 1129A) which appears to be the one relevant to my issue. “There is the potential for the AHRS to experience a reset every 90 hours of operation. When this happens, the system temporarily red-X’s attitude, heading, and slip/skid information for up to 45 seconds, and an annunciated disengagement of the autopilot occurs.” Further, “Garmin will correct this issue in a future software build that will be transmitted via a Cessna Service Bulletin.”
The problem was present in GRS 77 software version 3.01 and earlier and was resolved with the G1000 software update to version 0563.26 released in 2012.
This doesn’t really sound like your problem.
