Interesting NAV Source Lost Event

[daveg]

I recently got my airplane flying again after being down for 6 months installing structural "upgrades" (601XL).  I installed 5.3 software into my D180 with roll and pitch servos.  I had experienced the "NAV source lost" occurences last year without any fanfare as I would just reset back to NAV and continue on.  This past weekend was a little different.  At 5500' in smooth morning air, the autopilt was NAV tracking and ALT holding just fine.  While studying the map, the airplane suddenly went into a 10+ degree bank to the left.  I grabbed the stick and could feel the servo continually popping the torque plate since I was resisting it's desire to keep banking left.  I pushed the disconnect button. I saw there was a "nav source lost" message on the screen and the autopilot had switched to TRK mode.  

This failure mode threw me for a loop, almost literally.  Shouldn't the autopilot have continued in the same direction like it did in previous software versions?  What gives?  I do not like sudden un-commanded control inputs.

I can download and send the datalog if you wish.

Dave G.

 

[Brantel]

I think I recall that there are some settings as to what you want the AP to do if it fails down to another mode. You might want to check those settings.

 

[DBRV10]

And keep your heading bug set to where you want it. nothing worse in IMC having that set elsewhere and it drops into HDG or TRK mode while you are doing something else, not that you should be off the EFIS for very long anyway.

One instructor I know says never use NAV modes, fly it with the bug to maintain the track.

 

[dynonsupport]

Do you have the AP74?

 

[daveg]

No, I do not have an AP74, just one D180 and the pitch and roll servos.

Dave G