Cessna Single Piston Undifferentiated or Other Model
Flight Crew Flight Instructor; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 82; Flight Crew Total 11800; Flight Crew Type 4500
Aircraft Equipment Problem Critical
General None Reported / Taken
ATC Equipment / Nav Facility / Buildings; Aircraft
My Cessna is nearly unique at this point because it has both a Garmin GDL-88 supplying a Garmin GNS-430 (TIS-B) and an Avidyne TAS-600 (TAS) displaying on both a Garmin GTN-750 and an Avidyne MultiHazard Display (MHD).  [Southwest of CMH descending through 2500 feet]; the TIS-B produced a TA for traffic inside of a mile and 200 feet below me at 1:30 o'clock and on an intersecting course.  No traffic was seen out the window at the 1:30 position.  The TAS did not see any traffic at 1:30 o'clock but did locate traffic inside of a mile and going away (same vector as the TIS-B) at the same time as the TA and at the same altitude (200 feet below me) but at the 7:30 o'clock position.  This traffic was confirmed by visual sighting.  It appears that the TIS-B misplotted the location of the traffic and generated a fallacious TA.  TAS data appears to have been correct.  This circumstance repeated itself about 2 minutes later without a TA with TIS-B traffic at 2 o'clock and a mile and a half at 500' below my altitude.  No traffic was seen at the TIS-B report location but new traffic was confirmed at the same altitude and vector on TAS at 8 o'clock and a mile and a half.  It appears that the TIS-B uplink provided incorrect locations for ADS-B traffic that was simultaneously painted by TAS and visually confirmed at the TAS reported altitude; position and vector.  TIS-B was incorrect and; in reduced visibility created a high accident potential situation because a turn away from the TIS-B traffic would have resulted in closure with the actual TAS traffic and the development of a potential mid-air collision scenario.
Reporter states that the erroneous indications occur about five percent of the time and is always when the ADS-B information is being uplinked (R).  ADS-B (direct) information is always correct.  The reporter also believes that the fault lies outside of his aircraft; possibly with ATC software.
Cessna pilot using both TIS-B and TAS for traffic avoidance reports erroneous target information from the TIS-B.  The TIS indicated traffic at 1:30 coming toward the reporter and TAS indicated traffic at 7:30 going away on the same heading.  The TAS traffic was visually confirmed.