Judging GPS Receiver Reliability...

I wonder if I could get a feel for the relative reliability of typical GA GPS receivers.

1) Has anyone ever had a GPS receiver fail in flight - not loss of signal but the unit itself decided to die?

1.5) What about lockups - the unit gets to a condition where it cannot repond to button presses?

2) Has anyone ever had a GPS receiver show up NOGO at preflight?

3) Any experiences of GPS signals suddenly becoming unusable or significantly reduced accuracy during flight? If so, how long, how unusable?

Thanks in advance,

You didn't ask this one, but I have had a GPS receiver (Garmin 396) completely lock up during flight. Had to remove the battery to get it to restart.

396 failures

Same here, multiple 396 in flight lockups (buttons would not respond). I had to send two 396's back, but haven't had a peep of a problem from the one I have now, and it's been solid for over 18 months.

A few years ago the GX55 in my Bonanza went bezerk on the takeoff roll from LGC. Shortly it show me passing 400 knots, the map seemed to tie into the high speed. By the time I reached home it showed me over the ocean. Called Garmin and they had me do a hard reset. No problems before or since, 8 years and 2000 hours.
Couple times a year it will show me 50 miles off course for 15 seconds or so. Garmin said it was great technology, not perfect.

A friend had his 430 go goofy on him, turns out the data card went bad.

I also have a 430, and have seen the RAIM warning a few times, usually only for a few seconds. But, speeds and positions have been corrupted during those periods. This is why for gps approaches, a RAIM system is highly suggested (Receiver Autonomous Integrity Monitoring).

Lockups?!? Yikes!

BrickPilot said:

Same here, multiple 396 in flight lockups (buttons would not respond). I had to send two 396's back, but haven't had a peep of a problem from the one I have now, and it's been solid for over 18 months.

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OK, I guess I hadn't thought of asking about lockups - I would have liked to think that anything meant for an airplane (or made by Garmin!) would have software of sufficient quality that it NEVER locks up. Guess I need to ask.

...it amazes me that airplane software can be considered ready for the end user that is in any way shape or form able to "lock up". Speaking as a software engineer, there really is no excuse for that... Yikes!

OldAndBold said:

...it amazes me that airplane software can be considered ready for the end user that is in any way shape or form able to "lock up". Speaking as a software engineer, there really is no excuse for that... Yikes!

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But it happens! Doesn't it...

Solution --- take along "two" GPS's, for those momentary glitches.

Earlier in this thread I reported on my Garmin 396 lockup, but I forgot that earlier, my panel-mount Apollo 360 (now Garmin) unit failed in a more dangerous way. It started showing high speeds and erroneous positions, but gradually. That took a trip to the factory to fix.

Many years ago, I had a Loran start to show very subtle but worse and worse errors on an IFR flight. This was a flight along the US Mexico border and I am glad I didn't make any bad mistakes.

At this point, some sort of cross-check is certainly necessary. I guess that is a big point of the IFR units.

L.Adamson said:

But it happens! Doesn't it...

Solution --- take along "two" GPS's, for those momentary glitches.

Click to expand...

That's why I have three different GPS's in my system - all with different software.

And if the constellation goes away....I still have VOR.

If THEY go away, I have two Comms to call for help.

It's all about having a backup plan - never be totally dependent on any one thing.

Paul

Shouldn't happen.

Ironflight said:

That's why I have three different GPS's in my system - all with different software.

And if the constellation goes away....I still have VOR.

If THEY go away, I have two Comms to call for help.

It's all about having a backup plan - never be totally dependent on any one thing.

Paul

Click to expand...

Point is, that not one of the three different GPS's software should ever do what I am hearing that it can do. Troubling. Between hardware watchdog timers and multi-tasking OSs there really isn't a good reason why a user should ever see the system lockup. Need some better software architecture over there at Garmin I think.

I was in an interview recently for a software job in SF. The firm was developing wearable computers for soldiers. It was based on Windows. The guy had no problem he said with getting Windows programmers, but a hard time getting embedded programmers. "It's easy" he said, "to teach an embedded programmer how to do Windows. It's hard to teach a Windows programmer to do embedded." I fear that too much of the Windows mindset is filtering into embedded programming (and our avionics).

"We don't know why your unit locked up (they should!). Try cycling power and see if that clears the problem (the software should already be able to do that itself!). Otherwise, send it back to us and we will install the latest firmware and hope that fixes the problem (they should already know for sure if it will fix the problem!)." Sheesh...

Perfection is an admirable goal John, and I salute those who strive for it. However, I have been in the aerospace vehicle flight test business all my life, and have yet to find the vehicle, system, machine, or piece of code that I would trust NEVER to fail. Make it idiot-proof, and someone will invent a better idiot.

Or better yet, give it to us Ops guys....and we'll figure out a way to break it! (I'm not saying that is a good thing....)

Paul

Ironflight said:

Perfection is an admirable goal John, and I salute those who strive for it. However . . .
Paul

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Several years back, I inherited a embedded Java based flight display for a fighter aircraft photo recon pod. Both it and the system it was a part of were a nightmarishly bad design prone to frequent lockups and total system crashes. In particular, I knew that just three or four of the right button presses would lock up the system - not because the display software was wrong but because the rest of the system couldn't handle the inputs correctly. I tried to point this out to the manager but he objected saying that the pilot was supposed to know better than to press those buttons in that sequence. I felt bad for the poor flight crews that had to take that system out into the desert in Iraq at the beginning of the war and remember not to press the wrong buttons as they were trying to avoid SAMs.

The point is that there is a mindset in the (US?) aerospace industry now that thinks that it is OK and even unavoidable that the software occcasionally locks up or crashes. It is neither acceptable nor unavoidable nor even difficult to avoid. Perfect software? No. But highly fault tolerant? Definitely do-able. Like being able to detect and recover from a fault in between keypresses - should definitely be do-able.

When I started this thread I was expecting to find out that the GPS receivers were highly reliable and that almost noone had had any problems in flight. I am a bit suprised by the responses thus far.

(You should be able to tell that I am stalled waiting for a new R-710 to arrive...)

Unfortunately I think you are hearing from the "few". I've been flying with several different GPS systems since they became popular in the early '90s and have never had one "lock up".

Mel said:

Unfortunately I think you are hearing from the "few". I've been flying with several different GPS systems since they became popular in the early '90s and have never had one "lock up".

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Owned three aviation data-based moving map Garmins, and one non-aviation Garmin model since 1993. No lockups either. The last is a 296, which gets more use in a ground vehicle, but still no lockup.

L.Adamson said:

Owned three aviation data-based moving map Garmins, and one non-aviation Garmin model since 1993. No lockups either. The last is a 296, which gets more use in a ground vehicle, but still no lockup.

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OK, good, like I said I am just trying to get a feel for things. Thanks.

496 Failure

I had a brand new Garmin 496 die on me. Called the distributor down on the Gulf Coast and they had me try a few things and then said send it back. They replaced it with a new one as soon as they received my broken unit. It had about 5 hours on it and when it would switch on, the screen had a vertical stripe and it was frozen.
I also have a GXS250 and a map..