Hello all,
I have a minor issue with a G1000 equipped DA40D which I fly regularly. The ramp I startup the aircraft on is not level and so AHRS alignment is always a bit off, usually resulting in it thinking I’m in a slight roll when the aircraft is in fact level. This isn’t too much of a problem as I just reference the backup AI which I’m able to erect after I’ve taxied onto a nice flat taxiway. I’m wondering though what the correct procedure would be to re-align the AHRS after startup. Is simply pulling the PFD breaker the way to go or is there something in the menus. Having read the Garmin manuals a couple of times I can’t find mention of any procedure.
How steep is the angle of the ramp? My understanding was that the AHRS is supposed to self-correct for “small” slopes. That’s also how an in-flight alignment is possible after an in-flight reboot of the system (e.g. after a transient power failure).
I never see anything more than about 3 degrees discrepancy and sometimes it is level depending on where the aircraft is sitting on the ramp.
I’m flying on Sunday so I’m going to try this and will report back. I’ll taxi off the dodgy ramp, swap my ATC frequency on to COM2, pull the PFD breaker wait a couple of seconds and then pop it back in again. Hopefully that gets me an AHRS re-align and a nice level AI.
It realigns itself but to reset the AHRS breaker would make it align. Are you sure it is correctly calibrated? That is a maintenance action.
I don’t know, this is an aircraft which I rent so I don’t know much about the maintenance. Also it doesn’t always happen, the ramp is sloping and uneven so it really depends where I tow the aircraft to on the ramp before start. I’ve also never noticed any discrepancy in pitch, only in the roll indication.
Apart from sitting on a flat ramp, you may also help intial calibration on the ground by leaving pitot/static covers on and checking that you have enough satellites for an accurate 3D fix with zero GPS velocity and avoid magnetic interference
Anything else will need an engineer look to level the aircraft and set offsets on pitch/roll 
I don’t know the G1000 but don’t you have to wait with the aircraft totally stationary for a few minutes? That’s what I have with the Sandel SG102 AHRS.
Peter wrote:
I don’t know the G1000 but don’t you have to wait with the aircraft totally stationary for a few minutes?
You do. We’ve seen cases of G1000 AHRS alignment failures when the aircraft has started taxying before alignment was completed.
Peter wrote:
I don’t know the G1000 but don’t you have to wait with the aircraft totally stationary for a few minutes?
The pilot training material for the G1000 says:
No, the AHRS/ADC can align while the aircraft is moving and even in flight at bank angles of up to 20°
And the alignment takes far less that “a few minutes”. I’d say something like 10s to 30s?
I have first-hand knowledge that a G500 will realign in flight, in cloud/IMC (somewhat turbulent, but not horribly so) when its power is cycled. However, time certainly feels longer during that time.
FWIIW, the G500 Pilot Guide (the G1000 is not online on the Garmin website…) says:
Fastest AHRS alignment is achieved with the aircraft stationary and with all AHRS inputs valid (3-D GPS position, magnetometer, and air data). During initial power up on the ground, no GPS position and/or magnetic anomalies are common. If the aircraft is taxied prior to AHRS alignment, alignment may be delayed until after a valid 3-D GPS position is available.
During in-flight alignment of the AHRS, minimize aircraft maneuvering. The AHRS will align with shallow banking and pitch angles (less than 20 degrees of roll or 5 degrees of pitch). AHRS alignment may not be possible during more aggressive maneuvers.
I believe the G1000 and G500 both use the same AHRS, the GRS 77.
