Rabbit Holes

Conquering unforeseen challenges when building, flying, and maintaining an aircraft.

This giant rabbit at Sacramento International Airport is 56 feet long and weighs over 5 tons. (Photo: Carol M. Highsmith)

Passengers using Sacramento International Airport (KSMF) in California are greeted by an enormous aluminum sculpture of a giant red rabbit hanging from the ceiling of the main atrium. It is 56 feet long and weighs over 5 tons. It is positioned such that if it were anatomically correct and gender specific (it isn’t), both it and users of the main escalators would be quite embarrassed. As a work of art, it is definitely a sculpture. As an attractive investment for taxpayers’ funds, it is still definitely a sculpture.

I can think of lots of beautiful things hanging from terminal ceilings around the country, like Charles Lindberg’s gorgeous Monocoupe at St. Louis Lambert, and many others around the world, but a rabbit? To each hare-port its own, I guess. I’m no art critic, but one of the more interesting aspects to me of this Lepus locura is that beneath it lies a giant stone suitcase with a swirling hole apparently disappearing into an abyss in which the levitated leporid will somehow disappear. I have to admit, the “rabbit hole” part speaks to me.

One definition of rabbit hole from Merriam-Webster is “a complexly bizarre or difficult state or situation conceived of as a hole into which one falls or descends—especially, one in which the pursuit of something (such as an answer or solution) leads to other questions, problems, or pursuits.”

Bingo! E/A-B aviation can match rabbit holes with any avocation. Inherent within the selection, building, and operation of our craft are, inevitably, various types of rabbit holes large and small just trying to entrap us. The key to well-being, project advancement, and/or spousal retention, is recognizing them for what they are, emerging intact, and relishing the conquest of the puzzle.

Staying Cool

Early on in my RV-10, project, I made the determination that I wanted to install air-conditioning. Having owned a certified aircraft previously in Arizona, I knew how brutal the summers can be, and I wanted to extend the flying season to year-round. Even though the A/C kit was specifically designed for the RV-10, I fully expected that there would be some additional challenges inherent to any aftermarket accoutrement, and there were. After getting all of the associated elements installed in the build, hoses, condenser, blower, vents, etc., the A/C compressor itself was the last component to finish the install on the engine and tie it all together.

Correct A/C compressor top. Incorrectly labeled and shipped compressor bottom.

Much to my dismay, however, it didn’t fit. I could get the pulley aligned in the front, but the aft end of the compressor wouldn’t clear the number two cylinder sufficiently. A proper gap from the cylinder meant that the pulley didn’t align. All of the mounting hardware, spacers, etc., all looked exactly like the pictures in the installation manual, but it still wouldn’t fit.

No room for error in compressor fit and alignment.

This is where the rabbit starts drawing you in. Thoughts invaded my head that I had messed something up somewhere. I called the vendor, Airflow Systems, and Bill Genevro was extremely engaged in helping me sort out the problem. My compressor looked exactly like the one in the pictures, and I verified the part number was correct from both the shipping document and label on the box (the unit had been drop-shipped from a warehouse supplier).

One of my first (rabbit driven) concerns was thinking back when I drilled the holes on the case accessory pad for the mounting bracket studs. I began to question whether I had misaligned something. Further into the rabbit hole, other dark thoughts invaded, such that the misfit was somehow a wide-deck/narrow-deck issue. I think there is something in pilot psyche that causes us to always consider the worst-case scenario and work backwards from there. At the nadir, I began to think that I had gone to a whole bunch of wasted effort on a third-party enhancement project that wasn’t going to come to fruition. At least, I briefly thought, I’d have nice airflow from attractive overhead vents, even if it wasn’t conditioned air.

Correct compressor installed.

Frustrated, I left the shop and went to bed. Lying awake, I couldn’t get the conundrum out of my head. Then I had an epiphany. It was simple math. Alignment of the compressor didn’t matter. The position of the bracket didn’t matter. Those were adjustable with washers and spacers. All that mattered was subtracting the length of the compressor from the width of the available space. If the compressor didn’t fit, then it had to be the compressor’s fault, not the engine’s. I got back up and went back out to the shop. I carefully measured the length of the compressor from front to back. I then went to the internet and was lucky enough to discover the technical specifications for the specific model of compressor that I was supposed to have been shipped. Much to my delight and relief, I discovered that my unit was about -inch longer than the technical specification for my prescribed model. This rabbit hole was caused by some cretin at the factory putting the wrong model compressor in the correctly labeled box that was sent to me. When I finally received the correct model and compared the two side by side, the difference was obvious (see photo) and, of course, the correct model fit and operated perfectly. Take that, carrot breath.

“What Should We Do, Pops?”

A few years and many refreshingly air-conditioned flight hours later, my wife, son, and I were embarking on a trip to Rexburg, Idaho, to hopefully catch a perfect spot to airplane camp and enjoy the much-ballyhooed solar eclipse. My son was flying and navigating while I tended to velvet-touch engine care. We had barely leveled off when my son mentioned that something didn’t appear right on the Dynon SkyView EFIS display. He was right. The display was showing a massive wind out of the west and a correspondingly large correction angle on our heading to maintain our northern course. In IMC, it would appear correct, just a huge wind and a requisite large heading correction angle to maintain course. Visually, however, we knew that what we were seeing on the instruments didn’t represent at all what we were actually flying. We knew the route by heart and were pointed right at Humphrey’s peak near Flagstaff, and were therefore headed due north. Furthermore, cloud shadows below us showed light winds out of the north, just as our weather briefing had forecast. Our flight instruments were showing a heading of approximately 45 degrees to the left of what we were actually flying. In the old days, in a traditional certified aircraft, we would have just slewed the dumb directional gyro to the whiskey compass and pressed on. Modern EFISes don’t work that way. Having endured the miserable experience of an in-flight compass gasket failure in a venerable C-206, causing a rancid mess, I hadn’t even bothered to install a traditional wet compass in the RV-10.

Smart suitcase in a stupid place.

Peering into this new rabbit hole brought up all kinds of conflicting thoughts. We were recently embarked on what would be a long cross-country adventure. From an aero/propulsion point of view, the airplane was operating just fine in clear daylight conditions over a route that we were both extremely familiar with. However, something with the flight instruments was definitely askew. Our options were to turn around and return home, land at the nearest “suitable” airport, or press on to our intended fuel stop in Bountiful, Utah. My thoughts were a combination of my normal concern for safe operation plus an additional factor of wanting to set the right example for my son who, while an airline pilot in his own right, had also been my student for his primary flight instruction and very well may end up with this airplane as his own someday (don’t tell him that just yet). In theory, the father/son relationship shouldn’t matter, but it did, as any father of a pilot will attest.

Standby alternator finally installed.

Just then he interrupted my thoughts with “What should we do, Pops?” We agreed to continue as we were as we talked through our scenario together. The airplane was operating just fine, weather was no issue, all vital systems were fine. It all boiled down to our compass, more specifically, our magnetometer, being considerably off. Navigation was no problem. Not only did we both know exactly where we were, but our map display was fine as well.

I briefly considered pausing en route for an airborne recalibration of the compass, but that would involve 360-degree turns and, even still, was no guarantee of success. We had two ADAHRS on board and therefore two magnetometers. The system was designed to compare and alert to discrepancies, however, no such alerts were being made. The system considered itself healthy.

Backup alternator regulator on interior subpanel.

I had just flown the airplane the day before, and everything had been fine. But now Rabbit holes were appearing.

One difference between yesterday and today was that I had updated the system software. Maybe some software glitch was causing the issue? No problem, because I always kept a backup of the old software on a thumb drive. For a very brief moment, I thought about rebooting the software on one screen in flight but quickly concluded that such was a very bad idea with nothing to gain.

While my son continued to fly us toward our destination, I continued to think about what was different about today’s flight from yesterday’s and how two independent magnetometers could possibly err simultaneously. Then the answer hit me as clear as day. I relaxed and enjoyed the scenery from my uncustomary position of the right seat.

Upon arrival in Bountiful, it took me just a couple of minutes to confirm my hypothesis. I pulled everything out of the cargo compartment. The last item was one of those fancy “smart” suitcases with an internal GPS and li-ion battery. It had been quite handy at OSH because its internal battery could charge my iPhone twice on one charge. This flight, however, it had been innocently but stupidly placed upright against the aft cargo compartment bulkhead, abeam and just inches away from my dual ADAHRS stack. I relocated the suitcase to the vacant passenger seat and turned on the master switch to confirm that we had escaped this rabbit hole unscathed. We had.

Everything was normal, and we continued what turned out to be an absolutely incredible eclipse trip without any other squawk or distraction. The smart suitcases have since been banned by airlines and, in my opinion, should be banned in general aviation as well (no matter how handy they are at OSH).

This is an example of modern technology insidiously weaning us off of old-school procedures. A simple DG check on runway alignment would have alerted us to this problem from the get-go. The good news is that we never stop learning.

To be clear, I would never critique anyone who would have turned around, diverted, or dropped the airplane off at an FBO and said, “Fix it.” All would have been prudent albeit perhaps expensive and could come with the sacrifice of an otherwise once-in-a-lifetime trip.

However, to be honest, in this case I am glad we didn’t abort. We flew the airplane first, analyzed the situation, took appropriate action, and maintained situational awareness, just like airline training departments teach. The formula works.

“Ehhhh, What’s Up, Doc?”

“Oooooo! I hate that rabbit!” He’s always digging his holes to entrap us. Fairly recently, I decided to put my vacant vacuum pump pad to use with a new backup alternator. The kit, from B&C Specialty Products, was complete with excellent instructions. To do the job right, however, does require quite a bit of work. Mounting the external controller on the cool side of the firewall as they recommend, as well as mounting the requisite additional activation switch and low voltage light, required significant disassembly of my instrument panel. (Note to newbies: When planning your switch rows, consider provisions for future additional switches).

After everything on the inside was taken care of, it was time to take care of the firewall forward business. I removed the plate over the access pad and found the female spline, just as the pictures illustrated. The attachment of the alternator is accomplished with three easy-access stud/nuts and one (bottom left corner) that, due to its location and shadowing by part of the casted support on the unit itself, is from H. E. double hockey sticks. Gaining proper access to mount a nut on that stud requires removal of SCAT tubing and pulling of a magneto and its associated PITA R&R considerations.

Once everything was complete, the mag installed correctly and timing checked, and the prescribed ground checks from the installation manual were accomplished, it was time to test the system. I started the engine, turned on the primary alternator, and noted the volts and amp indications. I then turned on the standby system, and everything was normal. Running up the engine rpm to run-up level, I turned off the primary alternator. The low-voltage light that was part of the system illuminated as advertised, but the voltmeter dropped to battery level, and the ammeter showed normal battery draw without any indication of any production from the standby unit. The rabbit started to snicker.

I reset all the switches and tried everything once again to no avail. I tried it a third time at even higher rpm. Nada. Mr. Rabbit started digging a fresh set of holes for me to explore.

Frustrated, I pushed the airplane back into the hangar. Since the cowlings were off, I was able to make a cursory inspection of everything that was firewall forward, and it was really pretty simple and appeared secure. There are only two wires, the B-lead and the single connection to the plug harness, which all seemed correct and secure.

There were several connections to the external controller, but that was mounted on the subpanel and would require partial disassembly (again) of my instrument panel in order to gain access. Since it was after hours, I decided to return fresh to the problem the next morning when I could interface with tech support.

By the next morning, I had convinced myself that there was no way I was going to get around having to again open up my instrument panel. At least it was preferable to pulling a mag in order to get the alternator itself off. After carefully inspecting all of the connections on the controller and moving the ground (one of two on the controller) to a better location, I called tech support at B&C, and after a check of the static voltage at the harness plug came in at the low end of acceptable, they offered to send me another controller. This would cause a delay of a few days, but hopefully it would solve the issue. At the very least, it would narrow down the process of elimination. The rabbit continued to scoff.

Fast-forward a couple of days and I had received the replacement controller module, managed to get it installed on my subpanel, and put my instrument panel back together. Anxiously, I pulled the airplane out again and fired up the engine, with a hope for electron production success. Nothing. The exact same dead reaction as the previous controller that was now sitting on the workbench.

The only positive accomplishment in this rabbit hole so far was ruling out the controller as the problem. During another consultation with tech support, we decided to verify whether the core of the alternator was spinning with prop movement. The openings in the alternator body for cooling are tiny, and it can be difficult to see the fins rotate. They suggested a trick of using half of a Q-tip to verify rotation (see photo). Moving the prop by hand, it quickly became evident that the core assembly wasn’t rotating with prop movement. Like many new clues in a rabbit chase, I was both relieved and frustrated. The supposition from tech support at this point was that something had caused the main shaft to separate at the designated shear point. Argh. Verifying this would require, once again, pulling a mag and gymnastically tackling the nut from Hades while the three easy ones snickered with the rabbit.

Finally holding the cursed alternator in my now bloodied-knuckle hand brought another clue leading to even more questions. A quick spin of the shaft showed that all was secure and spinning normally—another clue with another mix of emotion.

ide-by-side comparison shows accessory gear shaft length difference. The thrust button press-fit one shaft but not the other.

Correct accessory gear in adaptor housing.

The next logical target was the accessory pad itself. Watching the coupling while turning the prop showed that the two were not interconnected like they were supposed to be. Dayum. The rabbit in my head started making “cha-ching” sounds.

It was now time to pull off the accessory pad coupling assembly itself. Hey, at least all four nuts were easy to access. Inspection of those parts, with my engine builder on the line, revealed that a spacer cap normally pressed into the end of the accessory gear shaft that aligned it with the drive gear was missing; therefore, the two gears weren’t meshing. A new spacer cap was sent my way. When it arrived, I finally felt that the problem had been solved, but alas, such was not the case. The rabbit wasn’t roasting on a spit yet. Trying to reassemble everything with the spacer cap now properly attached brought an entirely new problem and even a penultimate answer. When the accessory pad assembly, housing, case spacer, gaskets and gear, plus the alternator itself, were mounted back on the studs, the ensemble wouldn’t mate up flush. There was about a 3/16-inch gap at the aft gasket.

Checking shaft coupling integrity by using a Q-tip to show cooling fan movement when turning the prop.

I don’t know a lot, but I surely knew that something was amiss and resisted (properly) any temptation to try and force it together with the mounting nuts. I took the entire assembly apart once again and laid it all out on my worktable in mounting order. By process of elimination, it came down to the gear shaft itself, which had to be too long to allow everything to fit together properly. The shaft of the gear had a part number engraved on it. With a little research, the part itself showed up as a legitimate part for my engine series, but there was also another very different part number that was also listed. Mining down further revealed a eureka-moment discovery. The other part number was identical except for a slightly shorter shaft.

I was faced with another couple of days’ delay in order to get the proper part number I needed, but this time at least it felt that the dragon/rabbit had been slain. Sure enough. The new gear with the proper spacer cap fit exactly, and the entire assembly sandwiched together perfectly. Even Beelzebub’s fourth nut seemed to affix easier than normal.

Pulling the aircraft out for a final test, I didn’t want to let my optimism get in the way of cold, hard experience, but I soon cracked a broad smile when the shutting off of the primary alternator showed warm, fresh electrons from the standby alternator filling the void. Take that, cabbage face.

There were still a couple of voltage adjustments to make at the controller to get the system fully maximized, but after such an onerous rabbit hole experience, I don’t think I’ve flown a leg since where I didn’t test the standby system just to relish in the satisfaction of seeing the correct result.

Just in case…

Avoiding the Abyss

Anyone who embarks on the amazing journey to select, build, equip, and fly an E/A-B aircraft is going to have rabbit hole moments of frustration along the way. We just are. Some stumbling blocks get resolved in minutes. Others can take much longer. Anticipating that a few bumps in the road are normal helps prevent them from becoming infernal dead-end traps. The good news is that the more dark and foreboding a given rabbit hole ends up being, the more rewarding and satisfying the discovery of the eventual solution can be.

The following are some suggestions gleaned by decades of mentorship, hangar tales, helpful magazine articles, and bloody-knuckle personal experience.

  • Don’t panic. For every question there is an inevitable answer. Unlike the early experimental aircraft pioneers who got little more than pencil drawings and bauxite to work with, today there is a treasure trove of resources available to builders/operators. Factory/vendor tech support, EAA/AOPA resources support, tech counselors, fellow type builders, various online forums, etc. Chances are quite high that whatever rabbit hole in which one finds oneself, someone else has already extracted themselves from the exact same abyss.
  • Shave that rabbit with Occam’s razor. The ditty goes that often the most correct answer to any puzzle also happens to be the simplest. That’s certainly not universal, but it’s a great place to start. Pilot/builders are funny. Often when something isn’t how it should be, we first question ourselves on what we screwed up. And then our next question becomes, how much is it going to cost to fix? Sometimes we overreact, and in a zeal to solve the problem, we throw money at it. I would love to have a dollar for every expensive alternator, starter, or other peripheral that our community has replaced when the actual problem was a much cheaper switch, wire, connector, circuit breaker, etc. How many expensive inner tubes have been replaced because of a faulty (and cheap) Schraeder valve? The list is endless. Find a sturdy clamp in the shop/hangar, and put it firmly on your wallet before even starting to troubleshoot a problem. There’s a reason that experienced airline mechanics always check the circuit breakers first whenever called out to airline cockpits by airline pilots. It’s the same egg-on-face level of experience that causes seasoned airline pilots to check the circuit breakers prior to calling out maintenance.
  • When all the simple/cheap solutions are exhausted, don’t discount the bizarro. Sometimes, like being shipped the wrong part with the correct label, the rabbit lands a few punches.
  • Avoid working stressed or frustrated. Sometimes the quickest route to an answer to a puzzle comes from walking away for a break and returning to the chase relaxed, with clear eyes and fresh perspective. We never make our best decisions and judgments when under a gun.
  • Build it right. Operate it right. Maintain it right. Keep the rabbit at bay as much as possible by following correct procedures and using quality and correct materials, hardware, and tools. This is true in all aspects, but especially so in doing electrical work where a little extra effort early can prevent a huge amount of headache in the future. Good enough isn’t.
  • Enjoy the challenge, and don’t give up. There is tremendous satisfaction in troubleshooting a problem and then coming up with the proper solution. Don’t let the rabbit win.
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Myron Nelson
Myron Nelson soloed at 16 and has been a professional pilot for over 30 years, having flown for Lake Powell Air, SkyWest Airlines, and Southwest Airlines. He also flies for the Flying Samaritans, a volunteer, not-for-profit organization that provides medical and dental care in Baja California, Mexico. A first-time builder, Myron currently flies N24EV, his beautiful RV-10. He has also owned a C-150 and a Socata TB-9.


  1. Really enjoyed this article. You effectively conveyed the occasional frustration so well that I found myself getting upset, and then also enjoying your victories. Great humor as well…laughed out loud at “carrot breath” and “cabbage face”.


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