Garmin 430 Question

[groundpointsix]

Iot an error message this morning on the G430 that I couldn't explain and was hoping there was a garmin expert on the board who could explain what was happening.

We were shooting a GPS overlay approach of a VOR. About 15 miles north of the VOR we're cleared for the approach so my student loads the approach and hits activate, taking him direct to the VOR. We hit the VOR and start tracking the procedure turn outbound. So far everything is normal; the gps is cycling through the waypoints as expected. As we turn procedure turn inbound the GPS cycles into APR mode and the course scale begins counting down. As everything looks normal, I stop paying attention to the box and go back to monitoring my student.

As we pass the FAF inbound, the msg light starts flashing, so I hit the button and pull up a message saying "Approach not active." Sure enough, the screen shows us in terminal mode with a 1.0 scale. At that point I had us revert into VLOC mode for the rest of the approach, but I couldn't explain why it kicked us out of APR.

I know that if you lose RAIM the GPS will cycle out of APR mode and give you the same message along with the RAIM warning, but we did not get a RAIM message. Can anyone explain what happened here? I can't say for certain whether the scale ever got all the way down to .3 as I stopped looking around .8 or .7. I do know that my student was directly over the VOR and on course. The only thing I can think of would be that we didn't go out far enough on the procedure turn to give the GPS enough time to scale itself all the way to .3 scale, but we had a tailwind on the procedure turn and I would have thought we gave it enough time, also I've flown tighter procedure turns in the past and it's worked just fine.

 

[viper548]

I had that happen before. If you loaded but did not activate the approach, that could be the problem. The plane I had the problem in would do it consistantly, and I belive it was either a software or hardware glitch. I left the flight school before it got resolved. None of the other planes we had with the 430 did the same thing. Call a garmin rep, chances are it's a somewhat common problem.

 

[EatSleepFly]

I got a Garmin service alert (# 050721-00) in my mailbox the other day.

It says:

"In certain limited circumstances, conflicting navigation information can be provided when a selected 'Direct-to' waypoint is also a waypoint in a loaded terminal/approach procedure."

"The 'Direct-to' waypoint must be selected only by highlighting that waypoint in the flight plan and pressing the 'Direct-to' key. Do not use any other method of entering the 'Direct-to' waypoint."

It doesn't say what exactly happens, but it sounds like this might have something to do with what happened to you. Check Garmin's website, maybe there's more info. there.

 

[JediNein]

If you are doing S-Turns-About-An-Approach-Course, the Garmins will dump the approach mode as you cross the FAWP (final appproach waypoint). There's an earlier service letter about the problem.

Basically, the student needs to control the heading +/-10 deg while crossing the FAWP, even if it's wrong. If they pull a thirty degree heading change while crossing, game over.

Fly SAFE!
Jedi Nein

 

[convair007]

I flew a plane with an apollo IFR GPS. Same thing would happen any time there was a course reversal on an approach. There was a function to make the GPS get back into APR mode after the procedure turn though. Maybe Garmin has something along those lines. It's just a suggestion, I'm not too familiar with the 430.

 

[groundpointsix]

If you are doing S-Turns-About-An-Approach-Course, the Garmins will dump the approach mode as you cross the FAWP (final appproach waypoint). There's an earlier service letter about the problem.

Basically, the student needs to control the heading +/-10 deg while crossing the FAWP, even if it's wrong. If they pull a thirty degree heading change while crossing, game over.

Fly SAFE!
Jedi Nein

This sounds like it could be possibility. Is there a set distance on either side of the waypoint they need to maintain the heading? Does the gps calculate this based off of course or heading? I would assume course, but we have the avidyne system, so I figure it has access to heading information as well. If it matters, the needle was centered or very nearly so at the time of waypoint passage.

 

[JediNein]

From watching students weave their way around the FAWP, it only seems to be within .2 NM of the FAWP, but especially while crossing it. The off-course amount doesn't matter as long as the general track is crossing the waypoint. Having the students hold their heading from the moment the waypoint arrival starts flashing to just after crossing solves the problem.

The GPS is calculating track, TRK. That track must be towards the FAWP when crossing in order for the approach to be activated. It is not paying any attention to the Avidyne or on-board instrments for this calculation. This is how you can still do a coupled GPS approach without the PFD and/or AHRS systems.

If the track is changing rapidly but more away from the waypoint than towards it, the thing thinks you're not crossing it and refuses to activate. The 530 and 480 are the same way.

The hidden gotcha is when there is a turn after the FAF. The students must wait on their T's until they've crossed the FAWP. If they start the turn earlier, the GPS dumps approach mode.

Fly SAFE!
Jedi Nein

 

[groundpointsix]

Thanks for the info.