Any Unknown or Unlisted Aircraft Manufacturer
Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor
Flight Crew Last 90 Days 165; Flight Crew Total 9300
Communication Breakdown; Situational Awareness
ATC Issue All Types; Conflict NMAC; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
General None Reported / Taken
Procedure; Human Factors
During the approach to landing at ZZZ on runway XX; the TIS traffic warning on the GPS came on. I was at 500 ft and descending to the runway.  I believed it to be an 'echo' of my transponder; which sometimes happens; so I reset it and continued with the approach and landed (The conflicting traffic was showing +200 ft).  An observer on the ground came into the terminal office and asked to see the pilot of the flight that had just landed.  I introduced myself and he asked me if I had seen the helicopter over the airport. I explained that I could not see them as they were in the cloud layer and could not hear them; of course. I had made three position reports during my approach to the airport; but none were made by the military helicopter; which is not unusual.  It is my estimation that the crew of the helicopter turned on their transponder to let me know of their presence as they saw me on their traffic awareness system.  While it is not a common practice for the military to have their transponders on during operations; it would be invaluable for them to do so while on training missions that would get them close to civilian aircraft and airports.
Pilot flying on approach to land reports traffic warning due to a military helicopter over airport who was not making radio calls.