Garmin GPSmap 496 False Terrain Alert

Do any of you fly into KADS with a Garmin GPSmap 496? I'm getting a false
terrain alert when flying the Rwy 15 ILS and am wondering if anyone else has
this problem. I'm working with Garmin to resolve this, but so far what they
have suggested has not solved the problem.



When flying the approach the 496 makes the "500 feet" announcement just as
expected.



Next, an obstacle warning occurs which is OK, because of the upcoming
Addison water tower that is just to the east of the runway. The 496
announces "Warning, Obstacle ahead." Notice that this is just a warning.



Next, a Terrain warning occurs. The unit announces "Warning, Terrain ahead."
Then it alerts "Pull up. Pull up!" This should not occur. We're exactly on
the glide slope, with our normal approach speed of 120 MPH, and a 500 to 600
foot rate of descent. We're at an altitude of approximately 300 feet when
the Terrain alert occurs. This is very disconcerting to the passengers, and
if I was really flying the approach in IMC, you can be assured that this
would be extremely disconcerting to me! At no time during the approach have
we gone below the glide slope. Glide slope intercept at JERIT, the FAF at
2000 feet, confirms that our glide slope receiver is OK along with the
proper VASI lights as we get closer to the runway during the approach.



The 496 is fully updated with the latest software (V3.40 released Jan08) and
with the current Jeppesen database and the current Obstacle database. The
problem also occurred with the previous software version 3.30 and the prior
terrain database. The "nearest airport" criteria is set to the default, "All
airports" and the alert look ahead is set to 90 seconds. Everything else is
set to the default.



The unit does not give a Terrain alert when landing on the opposite runway,
33. Nor does it give a Terrain alert when landing at any other airport. This
Terrain alert including the command "Pull up, Pull up" only occurs when
flying the ILS 15 approach into KADS during short final.



Thus far the support fellow at Garmin (Todd) has verified the pertinent
options and settings in my unit, asked that I update to the latest software,
and update to the latest terrain database. This hasn't helped, and after
checking with the other support technicians, they are stumped.
Unfortunately, neither Garmin nor I have been able to get the unit to give a
terrain alert in simulator mode, but it does it 100% of the time in the air.



Anyone have any ideas? Has anyone flown with the GPSmap 496 into KADS with
audio alerts enabled and gotten the same terrain alert? Has anyone
experienced a similar problem at any other airport?



Thanks,

-Ron Gordon

Ron "at" GordonFamily.com

1968 V35A Bonanza N8485N