GRT HXr alignment time

Today at the run-up area I noticed my EFIS showed a right bank along with a constant
heading change and the map was also turning right. I returned to my hangar and restarted
the avionics and all seemed to be OK. I'm sure I had started to taxi befoe the AHRS was aligned
but I' ve done this before with no issues. I've even rebooted the EFIS before in flight and didn't see this
happen.

My question is, is there a time during the 2 minute alignment process when it is OK to move and not before?

Paul - two answers, both of which are intended to be helpful in the "teach a man to fish" category...

1) The SEARCH function here will turn up a few discussions on this topic, some of which contain pretty definitive answers

2) I would encourage you to join the GRT users forum (from the Support tab on the GRT web page at grtavionics.com) - the forum is monitored by the GRT team and often questions are answered very quickly and frequently with technical details which help in understanding how the systems work.

As for moving the airplane during alignment, the answers I've seen previously are that the first 30 seconds or so contribute the greatest amount to alignment accuracy.

BTW, I installed a backup battery that powers the two GRT EFIS units in our panel. in this manner they can be on and aligning while I'm running the pre-start and start checklists, then the backup battery ensures the units don't brown out while cranking. It doesn't take a very big battery to meet this requirement, with the battery fed through a diode and fuse/circuit breaker from the main bus. This allows the systems to be aligned and ready to rock by the time you're ready to release the brakes for taxi.

Hello Paul,

It is important not to move the plane during the first 10 seconds after power the AHRS. During this time the AHRS is correcting for the gyro bias. If the plane is moved or the AHRS temperature is rapidly changed during the first 10 seconds an uncorrected bias error can be introduced. This causes the heading change that you observed. The longer that you remain stationary, the better. This is because on the ground the AHRS does not get any assistance from either the airspeed nor GPS.

For an in air alignment keep the aircraft straight and level for at least the first 10 seconds after AHRS startup. Having Airspeed or GPS data will help accelerate the in air alignment process.

-Marc Robertson
GRT Avionics

I had I similar problem during climb out, my GRT sport showed the plane at a 90 degree bank climbing off the scale straight up. I turned it off for a few minutes then back on again and it eventually rest itself and was back to normal . The airspeed and altimeter seemed to be normal during the AHRS failure. Inspired me to purchase a back up attitude indicator immediately. Also I've been having trouble adjusting my altimeter bias, it reads about 80 feet below field elevation when set to AWOS altimeter. Im sure im probably doing something wrong but I've called GRT and followed the specified procedure 4 times with no change. Maybe it's a pitot static problem I don't know.

Reckoner said:

Hello Paul,

It is important not to move the plane during the first 10 seconds after power the AHRS. During this time the AHRS is correcting for the gyro bias.

Click to expand...

I'm sure this is what happened, Thanks for the info Marc.

Paul,
I had to learn the same thing during Phase 1. I tumbled the AHRS a couple of times due to moving too soon after engaging the avionics.

Since I fly IFR, I now make it standard practice to not move the plane until the horizon pops up. As you have seen, the standard is about 2 minutes but sometimes I get lucky with a 45 second boot.

A poster above talked about a separate battery power supply so one could turn on the GRT prior to engine start, etc etc. My electrical sys architecture is not built that way. My choice.

SO.. I usually get in, crank up and get the avionics booting while buckling in, sunglasses, visor, plugging in EFB, headset, listen to AWOS, raise flaps, adjust trim, etc. In other words, the boot time is not an imposition for me.

BABALU said:

I had I similar problem during climb out, my GRT sport showed the plane at a 90 degree bank climbing off the scale straight up. I turned it off for a few minutes then back on again and it eventually rest itself and was back to normal . The airspeed and altimeter seemed to be normal during the AHRS failure. Inspired me to purchase a back up attitude indicator immediately. Also I've been having trouble adjusting my altimeter bias, it reads about 80 feet below field elevation when set to AWOS altimeter. Im sure im probably doing something wrong but I've called GRT and followed the specified procedure 4 times with no change. Maybe it's a pitot static problem I don't know.

Click to expand...

For the AHRS issue, make sure that you don't move the plane for the at least the first 10 seconds after the AHRS is powered up. If the problem still repeats, contact our support and we will help you with the issue.

As for the Altimeter issue, be sure that the temperature is good and stable and the unit has been running for at least 5 minutes before performing the calibration. If the error doesn't calibrate out then you may need to send the unit back for repair.

-Marc Robertson
GRT Avionics

Thanks Marc, I will be sending it back soon anyway because I want to upgrade to the 8" Screen ,so you can check it out then ,thanks.