Dan, et al,

 

One late-September I was IMC eastbound over the rockies at 15,000 (2000 ft below the forecast freezing level) when I encountered light rime ice and received permission to descend to 14,000 where is was a bit warmer (Oat was 1C, went to 3C). After a while, I entered an exotic area of static unlike I had ever encountered before. Exotic because it wasn't just precip static, the clouds seemed to be peculiarly charged. 

 

I remained in this condition for at least 30-40 minutes although it seemed much longer.  Extremely sharp and loud pops were heard.  There was some whining over the VHF radio, but not extraordinary. The auto pilot (AP) GPSS function failed numerous times by indicating it had lost the ARINC steering signal from the Garmin 430 (GPSS flashing LED) although, from my observation, the 430 never failed.  I can't remember if the S-Tec 50 AP additionally failed independently of the GPSS problem, but the fix was to recycle power to the AP.  At one point, the AP completely failed leaving me with no backup mode -- thus requiring primary mode hand flying and occasionally using the attitude indicator (yeah, right). 

 

In another 15 minutes I entered a limited clear area over Casper WY and, with the prospect of more flight thru bad weather, I decided to land and get the problem fixed or wait for better weather.  ATC was very accomodating even though this was only the third day of GA flight after 9/11.  Fortunately, the avionics shop there could fix a blown internal micro fuse overnight.

 

The next day was more flight in the clouds - IMC all the way to about 10 miles shy of my home airport just west of Chicago.

 

Other equipment, Terra Com radio and transponder, Jim Franz's AOA, Vision Micro System's EPI 800 system, Mac Trim servos, RMI Micro-encoder, etc - all worked fine through this encounter. 

 

About 2 years later, I accidentally discovered a further problem with the AP.  The turn coodinator gyro tach indication was always positive so that the AP would "operate" whether the gyro was turning or not.  Traced to a bad component on the pitch board, it is only speculation that the same anomoly that took out the AP fuse also damaged this circuit.  To test for this problem, one should pull the breaker for the turn coordinator, initiate the AP power up sequence and turn on the AP.  If the ready light remains lit you have a problem - a dangerous problem if the gyro is lost in IMC and the AP takes you to an indeterminate attitude.........

 

As to Hamid's commentary on certified devices, note that my AP and GPSS were and are certified.  "Certified, TSO'd, etc." is no guarantee of your safety, although the device has at least been tested to some standard.