Baron 58/58TC
Flight Crew Multiengine; Flight Crew Private; Flight Crew Instrument
Flight Crew Last 90 Days 100; Flight Crew Total 1800; Flight Crew Type 700
Situational Awareness
Aircraft Equipment Problem Critical
Flight Crew Became Reoriented; General Maintenance Action
Aircraft
I had my pitot heat checked prior to winter and on prior flights. I was above icing at 10;000 ft. As I descended into minimal icing below 8000 ft. the pitot heat failed and the pitot tube iced up. I lost airspeed indication. This is a minor event with GPS ground speed on 2 GPS units to compensate. However within moments the AHRS started to malfunction and started intermittently cutting off heading information. Then at times it gave other error messages; flagged erroneous attitude indications and started falsely indicating 'dangerous' attitudes even during normal standard rate turns in the holding pattern. At one or two points the entire glass panel instrument display gave a fault and sit off all instruments (attitude; heading; HSI; glide slope; altimeter; etc.) requiring use of backup instruments. I was able to fly and complete the ILS approach using the intermittent indications; the GPS's (2) and backup indicators to minimums (300 ft.; 1/2) uneventfully. I contacted the avionics shop who advised me that loss of PITOT input ALONE can cause complete loss of AHRS FUNCTION; all modalities. The pitot tube was replaced and on the next flight I have had no problem. If this is true and loss of a pitot tube input can cause complete loss of the AHRS - loss of heading; attitude; HSI; altimeter; other vital indicators - especially in low IFR - this can become a very dangerous situation!! This is very bad engineering design without proper failsafe design. Loss of airspeed should allow a default mode that preserves indications of attitude; airspeed; the HSI; etc.!!!! This fault of the DESIGN could become life threatening to the pilot from what used to be a TRIVIAL problem in the past. The engineers can redesign this to have bester failsafe performance!
BE58 pilot experiences pitot heat failure descending through icing conditions at 8000 feet. Within moments the AHRS begins to malfunction along with other components of the glass panel display. Backup instruments and GPS ground speed are used perform an ILS approach to landing. The reporter is informed by his avionics shop that loss of pitot input can cause loss of AHRS function. He believes that the system should be designed to operate normally with loss of pitot input.