Here's the latest information on the issue with the Garmin GPSmap 496
reporting a false terrain alert when flying into KADS along the runway 15
ILS:



Garmin provided me with a current terrain database update, in an effort to
see if corrections that have been made in that database since June 2006
would correct the problem. It did not, though I certainly appreciated their
efforts.



Another pilot who occassionally flies into ADS who also utilizes his 496 for
improved positional awareness and has his 496 audio connected to his
intercom for terrain /obstacle warnings (not IFR operations) has reported to
me that the problem also occurs with his unit when he lands on runway 15 at
Addison. As with my 496, the problem is easily reproduced and occurs 100% of
the time. (Thanks! This was an important point of information for Garmin
technical support.) Another ADS pilot/owner has offered to plug his 496 into
my panel and permit me to fly with him and his unit to confirm that the
problem occurs with his unit in my installation. I'll do that on Saturday,
but we have every expectation that this will repeat, given the prior report.
It will provide a second confirmation. (In his installation, the audio alert
feature is not utilized.)



Garmin agrees that this evidently points to an errant data point within the
terrain database close to the approach end of runway 15. They admit that the
elevation data has errors which they continue to correct. No other airport
approach has been reported by anyone on the Internet as having this problem,
in response to my queries. (If you have experienced such a problem in a
repeatable fashion, Garmin is interested in the details.)



Garmin have asked me to download the recent tracks that demonstrate the
problem from my 496 and email them to them. They will use this information
as they document the problem to the FAA subcontractor who produces the
database that they then license, reformat, and resell for use in the GPSmap
units. I've done that, yesterday.



Thanks to those of you who assisted with the analysis and troubleshooting of
this problem thus far. The rest of you can continue chatting



-Ron Gordon