PT20J Posted March 4, 2021 Report Posted March 4, 2021 @Jake@BevanAviation, @Baker Avionics or anyone else got any ideas? Here's the setup Nav1 is a GNS430W Nav2 is a KX165 Nav1 and Nav2 are selected to the KAP150 autopilot via an Aspen EFD1000 PFD and associated ACU The GS capture by the autopilot has been intermittent on either GPS or ILS approaches when the GNS430W is selected ever since I purchased the airplane a couple of years ago. The autopilot captures an ILS glideslope reliably when the KX165 is selected The ACU was replaced when the HDG output failed and this didn't change the GS capture intermittency. The KC191 autopilot computer was replaced when it's microprocessor failed and likewise this had no effect on the GS capture issue. During all operations, the PFD displays correct annunciations and the localizer and glideslope indications are appropriate when either nav source is selected. Normally, I would suspect a wiring/connector pin issue with the ILS Energize signal, but since the problem only exhibits on the GNS430 which has an ARINC 429 serial interface to the Aspen PFD (which in turn has a 429 interface to the ACU), I'm thinking it must be something else. Skip
EricJ Posted March 4, 2021 Report Posted March 4, 2021 Time for an Avidyne slide-in replacement of the 430. It might not fix the issue, but it'll be nicer. 1
Jake@BevanAviation Posted March 5, 2021 Report Posted March 5, 2021 I have seen an isolated issue with some Gamin navigators where the ILS energize ground does not go low enough to keep the computer happy. Older analog navigators do not show this issue. In the past the solution was to provide a hard ground to the computer with the associated navigator via a relay. The navigator triggers the relay and the relay provides the ground to the flight computer. However, having the ASPEN in the mix throws this theory out the window. I would like to see a apples to apples comparison of the 430W vs the 165 both shooting a ILS approach. Personally I think if you were to look at the ILS ground to the computer from the Aspen ACU and compare the two (430W vs 165) using a nav generator for ILS signals you will notice something different. Could be a different voltage reading or resistance reading but my guess is something is different. The computer was built around analog signals, this issue might be related to all the magic that happens when taking a digital source to the PFD, another digital signal from PFD to ACU, and then the ACU changing it to analog to keep the computer happy. The amount of digital to digital conversions is different when looking at the wiring for the KX165 to the ACU. From the ACU to the computer the wiring does not change, the only thing that does change is what source is providing the signal to the flight computer (digital vs analog). 1
PT20J Posted March 5, 2021 Author Report Posted March 5, 2021 57 minutes ago, Jake@BevanAviation said: I have seen an isolated issue with some Gamin navigators where the ILS energize ground does not go low enough to keep the computer happy. Older analog navigators do not show this issue. In the past the solution was to provide a hard ground to the computer with the associated navigator via a relay. The navigator triggers the relay and the relay provides the ground to the flight computer. However, having the ASPEN in the mix throws this theory out the window. I would like to see a apples to apples comparison of the 430W vs the 165 both shooting a ILS approach. Personally I think if you were to look at the ILS ground to the computer from the Aspen ACU and compare the two (430W vs 165) using a nav generator for ILS signals you will notice something different. Could be a different voltage reading or resistance reading but my guess is something is different. The computer was built around analog signals, this issue might be related to all the magic that happens when taking a digital source to the PFD, another digital signal from PFD to ACU, and then the ACU changing it to analog to keep the computer happy. The amount of digital to digital conversions is different when looking at the wiring for the KX165 to the ACU. From the ACU to the computer the wiring does not change, the only thing that does change is what source is providing the signal to the flight computer (digital vs analog). Jake, that's a great thought. The KX165 should connect to /ILS Engage pin 2 on the ACU. The ACU outputs /ILS Energize to the autopilot on pin 5. Somehow internal to the ACU the digital ILS Energize from the GNS 430W has to get converted to an analog signal within the ACU and switched with signal from the KX165. So, most likely the problem lies either in the ACU or the wiring and signal level between it and the computer. Seems likely a wiring/grounding issue since it is intermittent, didn't improve with change of ACU and the ACU is installed way back in the aft equipment bay. The person who did the installation of the 430W and Aspen for the previous owner was not well gifted at crimping terminals. I've had to sort out a few other issues. Thanks. Skip
Baker Avionics Posted May 6, 2021 Report Posted May 6, 2021 Maybe try to switch the GS antenna connections at the splitter from the GS antenna between the 430 and 165. It sounds, to me, like it is not sensing a good ILS signal on the GS side. The "signals" between the AP computer and the ACU are pretty much moot as is the connections from the 430 to the ACU. If all other functions of the 430 are working good on the Aspen and the AP, all of it goes to/through the ACU and is transmitted digitally so it has no bearing on the wiring to the ACU or from the ACU to the AP due to the fact that the ACU alone feeds the computer the ILS Energize signal. That is a verification in itself. It seems like a RF signal issue that may be weak. via the receiver in the 430. Further, what are the setting for the Aspen/ACU and the 430 as it pertains to the Aspen? Does the Aspen have the overbraid shielding at least 12 inches from the PFD connector and is going to ground? That is probably where I would start. It doesn't seem like wiring is an issue, to me. The only other thing is are you selected for GPS on the 430 vs VLOC while doing the approach? Just curious. 1
Baker Avionics Posted May 6, 2021 Report Posted May 6, 2021 One other thing, what is the PN of the AP computer? Below is an excerpt from the Aspen Manual that may be a bit concerning, if applicable. The referenced note is specifically for the KFC100/150
PT20J Posted May 6, 2021 Author Report Posted May 6, 2021 Thanks, Greg @Baker Avionics. I think I found the problem. It appears that the ILS energize pin on the KC 191 connector was making intermittent contact. I tweaked it a bit and it has been good on the last few flights. I was waiting to see if it stayed fixed since it was intermittent, but I think it's good now. Skip
Baker Avionics Posted May 6, 2021 Report Posted May 6, 2021 Just now, PT20J said: Thanks, Greg @Baker Avionics. I think I found the problem. It appears that the ILS energize pin on the KC 191 connector was making intermittent contact. I tweaked it a bit and it has been good on the last few flights. I was waiting to see if it stayed fixed since it was intermittent, but I think it's good now. Skip So cool! Good job! It is just super odd that the same pin would cause only the 165 to work solidly. LOL....Kudos!
PT20J Posted May 6, 2021 Author Report Posted May 6, 2021 4 minutes ago, Baker Avionics said: So cool! Good job! It is just super odd that the same pin would cause only the 165 to work solidly. LOL....Kudos! Well actually, I'm not sure about the KX 165. I was pretty sure it was working but when I tried to repeat it neither radio GS would capture. Intermittent issues are so much fun
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