Negative Transference: Jeff and I drew up a plan with Lancaster Avionics and went out to test our YAW Damper and missed approach procedures. Based on discussions with Jim and Jeff, I’ve decided that my procedures were suffering from negative transference. The autopilot and NAV/Comms in my own airplane are more capable when it comes to automated approach procedures, in my opinion. In any case, the capabilities and required procedures are different between the two systems to make a real difference.
Fixing the Data Card Slot Issue: My theory on why the data card slots weren’t working starts with new data cards I had ordered as backups for the one that we had for each unit. Now each Nav/Comm has a backup data card, allowing me to manage them from home and simply swap cards. There is more to it than that, but you get the idea.
When I inserted the new card into the slot, I noticed that it stuck for awhile when ejected. Upon closer inspection, the label had peeled back and was catching on the sides. I scraped off the label to be able to use the card, but didn’t clean off the adhesive holding it. That adhesive transferred to each of the slots, as I was checking for resistance back and forth. I believe that adhesive was causing this issue, as I had used a high powered flashlight to peer in. There was no paper left behind and not visible obstructions.
I broke some electronic cleaner with me, but didn’t want to just press on without talking it out with Jeff first. Jeff asked some great questions, and we discovered the fast-evaporating electronic cleaner is not safe to use on polycarbonate plastics. Furthermore, Jeff made an incredibly important point that the displays might be even more sensitive to this chemical. I shuttered a bit after he said that, remembering that someone had ‘cleaned’ the screens on a Cirrus Avidyne system with something that completely ruined them. The electronic cleaner went back in the car.
We decide that isopropyl alcohol won’t hurt, and would an option. What ultimately worked, however, was two things. First, thoroughly clean the data card where the sticker peeled off. Second, apply small amounts of a dry lubricant to the plastic portion of the data card (opposite side of the contacts), and insert and eject the card multiple times.
The dry lubricate degraded the adhesive that was left behind from the torn sticker, and now both data cards began working flawlessly. I left everything set up for our trip, and will test the ejection and re-insertion process after we get this trip behind us.
We are legal and fully updated for charts and navigation. All radios are up to date on operating software, except for the G600Txi, which we will follow up on.
Operational Testing Plan: The YAW Damper will be tested during the entire flight today, but we already know that it works and can be turned on and off easily. My focus today will be on flying fully automated approaches and documenting the required button pushing to make the system work.
We’ll fly several RNAV 27 approach into Delaware Airpark (33N) with flight following with Dover. Old crew procedure was to use heading mode to walk the airplane onto the final approach course, and then use approach mode from there. I firmly believe that this autopilot should be able to make the turns (even tight turns) with the Nav/Comms and interfaces, so we’ll try that.
Questions we are looking to answer:
- Will the GPSS guidance and the autopilot be able to work together through the final approach course?
- Will the GPSS mode with Heading and GPSS selected on the control head capture the vertical guidance?
- Does Approach Mode need to be used at all?
- How will the transition to the missed approach take place. How will that be activated?
Will the GPSS guidance and the autopilot be able to work together through the final approach course? Absolutely. We flew three approaches at various speeds, and in every case the GTN750 calculated the required sharp turn and the autopilot followed it.
Note that selecting APPROACH mode when cleared for the approach does not work unless you are straight in. This was true at least for todays experience. Leave the GPSS mode active until the turn onto final approach course, and then select APPROACH mode.
Note also that to follow GPSS mode you need Heading Selected and GPSS mode selected and CDI set to GPS on both the GTN750 and the G600Txi. My airplane automates this integration entirely, and switches modes automatically on an ILS with GPSS entry.
Will the GPSS mode with Heading and GPSS selected on the control head capture the vertical guidance? We did several tests and couldn’t make this work. I believe you have to select approach to follow the vertical guidance, with one cavaet.
While testing, I found that with this system you must give the autopilot permission to descend below the altitude you are currently set at. We did not achieve a successful test that showed the heading modes ability to capture a glideslope. Admittedly, we discovered on the second approach that you have to set the FAF altitude on the selector to give the autopilot permission to follow vertical guidance for this LP + V approach. My airplane doesn’t honor the altitude and follows the approach vertical guidance when the approach has been activated.
Does APPROACH Mode need to be used at all? Yes, but not until you are on the final approach course. The APPROACH mode cannot make the sharp turns to get you onto final, so use GPSS up to that point. Give the autopilot permission to descend by setting the FAF altitude at the appropriate time. I further believe that this change to APPROACH mode needs to be accomplished 2nm prior to the FAF (based on experience in other aircraft).
The procedure stated above works, and I’ll use that going forward.
How will the transition to the missed approach take place? How will that be activated? When I’m flying an approach, I disconnect the autopilot at 500 agl and hand fly it from there. Upon reaching the MAP, I execute CRAM, CLIMB, CLEAN, COOL to get the airplane climbing according to the Missed Approach Procedure.
The GTN750 presents option boxes at the MAP, asking you if you’d like to continue in GPSS following the Missed Approach Procedure. I press that option and activate navigation (my airplane does this automatically).
Next up, I make sure the MAP page of the GTN750 is showing GPS and not something else. Likewise I check that on the G600Txi, and I also look at the heading bug ICON which should show that GPSS is active. I check that the Missed Approach Altitude has been set in the selector, and press the ALT Capture to activate the flight director for that altitude. Finally, I turn on the autopilot and this process will successfully fly us into the hold at the proper altitude.
Note that capturing the altitude precisely requires a few rocker inputs on intercept rate as you go, but that is small potatoes and normal for older equipment.
Conclusions: The work we’ve done in cleaning up the squawk list has made major improvements to this airplanes capabilities. This work will considerably reduce workload for the PIC in times of challenging weather in busy atmospheres.
- The autopilot works in every respect, and is actually pretty good.
- ILS approaches can be flown using the very same procedures. Allow GPSS to get you to the final approach course, and then use approach mode.
- GPSS mode does a nice job of tight turns and automating approaches and missed approaches.
- Lancaster Avionics is a trusted source for maintenance.
- NAV/COMM radio updates might not be a bad idea as a next step. Upgrade the GTN750 to a GTN750Txi (faster processor, better display, improved integration) and swap out the Garmin 530W for a GTN650Txi (continued maintainability, faster processor, better display, cross talk integration with the GTN750 Txi). Doing this now will set us up to be fully integrated with a new GFC600 autopilot when it becomes available.
Fly Safe!
Frank