Narrative:

After descending out of 16;500 ft MSL; I was on final approach to land using the PAPI for final guidance to runway 25R. I heard numerous radio transmissions from lvk tower to an aircraft that didn't have an operable transponder and [such] garbled radio transmissions I couldn't make anything out.I asked for a position report for the aircraft in question. I was told it was possibly over a local landmark. I continued on the approach. I was told the aircraft was originally scheduled to arrive at mid-afternoon for an avionics repair of the transponder; it was now late afternoon and dark. As I reached short final; I received a tis alert for traffic right in front of me at +100 ft. I again asked for a traffic update and was told no traffic was visible from the tower airborne at that position. Next I received a tis alert of traffic right in front of me at -100 ft.after landing; and clearing the runway; I heard the tower controller asking an aircraft that had landed if they wanted to clear the runway to the north or south and to 'click' the mic once for north and twice for south; maybe reversed on that; but you can get my meaning.after I put the aircraft away and before driving out I called the tower and asked a controller what had happened. I was told the aircraft in question was supposed to have arrived in daylight hours with an inoperative transponder. They further advised the aircraft had been orbiting the runways above without an operable transponder; no lights on and with an inaudible radio. They said the pilot did see me on approach with my lights on and had landed immediately behind me. The controller said that none of the personnel in the tower saw [the aircraft visually]. Makes sense; it was dark out and that aircraft had no lighting!why was an aircraft; with a known problem; flying after the sun had set with no lights; no transponder and no usable radio?the only thing I can surmise is the transponder was so weak the tower's 'bright radar' could not pick up the signal; the aircraft's electrical system was so weak the radio would not transmit properly and the transponder was just powerful enough for me to get a traffic alert when in very near proximity to it.

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Original NASA ASRS Text

Title: A Citation single pilot on a night time final approach to LVK appeared to have encountered an aircraft; also on final; which was operating without a transponder; no external lights and compromised communications capability.

Narrative: After descending out of 16;500 FT MSL; I was on final approach to land using the PAPI for final guidance to Runway 25R. I heard numerous radio transmissions from LVK Tower to an aircraft that didn't have an operable transponder and [such] garbled radio transmissions I couldn't make anything out.I asked for a position report for the aircraft in question. I was told it was possibly over a local landmark. I continued on the approach. I was told the aircraft was originally scheduled to arrive at mid-afternoon for an avionics repair of the transponder; it was now late afternoon and dark. As I reached short final; I received a TIS alert for traffic right in front of me at +100 FT. I again asked for a traffic update and was told no traffic was visible from the Tower airborne at that position. Next I received a TIS alert of traffic right in front of me at -100 FT.After landing; and clearing the runway; I heard the Tower Controller asking an aircraft that had landed if they wanted to clear the runway to the north or south and to 'click' the mic once for north and twice for south; maybe reversed on that; but you can get my meaning.After I put the aircraft away and before driving out I called the Tower and asked a Controller what had happened. I was told the aircraft in question was supposed to have arrived in daylight hours with an inoperative transponder. They further advised the aircraft had been orbiting the runways above without an operable transponder; no lights on and with an inaudible radio. They said the pilot did see me on approach with my lights on and had landed immediately behind me. The Controller said that none of the personnel in the Tower saw [the aircraft visually]. Makes sense; it was dark out and that aircraft had no lighting!Why was an aircraft; with a known problem; flying after the sun had set with no lights; no transponder and no usable radio?The only thing I can surmise is the transponder was so weak the Tower's 'bright radar' could not pick up the signal; the aircraft's electrical system was so weak the radio would not transmit properly and the transponder was just powerful enough for me to get a traffic alert when in very near proximity to it.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.