iflyabeech

I have been getting false terrain and obstacle warnings while landing RWY35R in KAUS. These happen under 500ft while on the ILS. Pretty annoying.

The warnings I get are similar to the ones described in this thread on another forum: Garmin GPSmap 496 False Terrain Alert - AviationBanter

I currently have an email exchange with Garmin on this issue, but we haven't gotten anywhere yet.

Has anyone else had this problem with a 496 at Austin or any other airport?

RVSM Certified

Hello iflyabeech,

What you most likely already know with no help from anyone, is that the 496 is classified as an "aviation portable" and this is not an integrated component of a composite "glass" or EFIS. What you also most likely know is that the refresh rate is only 5 hz. So, it is not fully-integrated EFIS grade GPS.

What you may or may not know [yet] is the the core technology embedded into these portable devices. While it may do a good job of guiding you to the nearest Omni Hotel while out on the highway in your car, it might not be such a reliable ground proximity warning device while flying an actual instrument approach.

I'm not yet a pilot, but I did spend a short career [10 years] in the enterprise software business and I do have some familiarity with the object oriented code that goes into produce like these.

If you read the software license very carefully, you will find something extremely important to you as a pilot. Garmin tells each user that their technology is not mission critical. They don't actually use those specific words, but they do say that they will not "warrant" either "performance" and/or that the source code is "error free."

The 496 is also not "certified" for use in General Aviation Aircraft - but, I'm sure you already knew that. The key here that I'm trying to help you with is the lack of "mission critical" technology onboard. I'm not a pilot, so I would not ever try to tell you what you should use, but if I were in an aircraft when these false alerts went off as your passenger, I would be very concerned to say the least. I don't for one minute think that you are using this as an instrument approach tool, but I just thought I would throw that "mission critical" statement into the mix here, just for good measure.

I've done a lot of homework on what is certified and what it not, who offers mission critical GA glass/EFIS technology and who does not; all because I had initially planned to include some of this same type of technology into the aircraft that I will eventually own and fly.

My guess is that you use this portable as a conceptual aid only and not for any real navigational purposes anyway, right?

These types of portable GPS devices are not as electronically shielded as the integrated certified modules. The 496 especially can have its link to the satellite knocked out by RF interference from other equipment onboard, as well as Radar and ILS equipment located on or near airports. Since you say that you are getting false indications near the approach end of the runway, it could very well be the case that this particular approach, has Radar/ILS eqipment projecting RF on a plane/angle that intercepts the approach path of your aircraft, knocking out the link for a period of time.

If you combine the nominal refresh rate of 5 hz with the "potential" RF interference coming from the approach end of the runway, this might/could account for the false terrain alerts on "this" particular runway and at this particular airport. Your onboard Radios can also, at times, act like an Electronic Counter Measure against your portable GPS link to the sattelite - again, through RF interference. Certain radio frequencies can cause this to happen. Again, combine this with a paltry 5 hz refresh rate and it could translate into a false terrain warning.

That's about all I can do with this one - hope this helps.

iflyabeech

not really.. I understand the concept of GPS and this is a backup to my onboard IFR Garmin 400 and onboard weather radar.. The terrain is a bonus. I don't carry passengers, but from my actual flying experience, except for this one set of occurrences at this one runway, the Garmin 496 performs as good or better than my IFR certified Garmin 400 panel mount GPS and the terrain functions are as good as any approved GPWS units that I have flown with.

I am not really looking for technical data.. Just wondering if others have had this issue at Austin or other airports.

RVSM Certified

I've always understood that technical details cause technical problems in technical products/applications.

If you can isolate the problem down to one airport [in your specific case you already have] then that automatically eliminates a number of impossible answers to the problem.

Garmin has an list of current radio frequencies that cause problems with the 496. This could be a source of the problem, given some of the uniqueness in frequencies at various airports, if one or more of those frequencies are utilized in your aircraft on or around this particular airport.

The error message itself is not necessarily indicative of the source of the problem - especially with type 1 errors that come from human generated code.

But, if all you want to know is if other pilots are having the same or similar problem and you don't care to fix it, this probably won't help much either. Good luck with that.

iflyabeech

Thanks. You are right...I am not interested in scanning the radio frequency band in search of errant frequencies.

Next....

billyreytexas

I got both a terrain & obstacle warning at the end of runway 17 at SGR while taking off. There is an ILS for 35. Maybe that explains it.

It was dark and very shocking to hear that there was an obstacle where none had been only minutes before and then to get a terrain warning during a climbing turn over flat land. These warnings were between 500' & about 700' agl.