For those of you that have STEC autopilot systems please read  SAIB 60-21 attached below. The STEC autopilots use the TC for "attitude" reference. Their sales literature tell you how much safer this is over the attitude reference systems other manufacturers use (like King). Unfortunately, STEC does not tell you that if the TC ground wire becomes disconnected or the TC loses the ground signal the AP will still operate by slowly rolling the aircraft one way or another (albeit without an attitude reference). This can pose a big problem in the cockpit if you are IMC (the AP "ready" light is on but the TC is failed) and can cause a pilot to lose control of the aircraft. It is my opinion that this has been the cause of at least two fatal accidents and one serious accident. The survivors of the serious accident -- two instrument rated pilots related how confusing it can be to fly with the AI going one way and the TC going the other way.

 

Unfortunately, STEC is currently fighting one of these cases Federal Court in NJ where I have testified against them and has chosen to not inform its customers of this potentially deadly problem.

 

Fly safe,

 

Jeff