By Vic Syracuse, EAA Lifetime 180848

This piece originally ran in Vic’s Checkpoints column in the October 2023 issue of EAA Sport Aviation magazine.

As a designated airworthiness representative (DAR), one of the things I tell new builders during the initial airworthiness inspection is that they shouldn’t trust the aircraft until it has at least 100 hours on it. That’s been my experience over the years, even though I strive to build quality aircraft.

Each amateur-built aircraft is different. They are mechanical devices with lots of moving parts, and it takes time to figure out some of the weak links. Sometimes it’s just a matter of adding some chafing protection to a tube or bundle of wires, and sometimes it can be bigger. Don’t forget that most of the time there is a brand-new engine up front, and it is still breaking in during those first 100 hours. Let’s hope it was assembled correctly, but as we’ve seen lately in the industry, that’s not always the case.

It’s funny to me that whenever I’ve come out of flight training, whether it’s that first certificate or a new rating, I’m always expecting something to happen to the aircraft. Probably because for the last so many hours, it’s been all about failures and how to correct for them. That’s what good training is all about.

As for my helicopter flying, even with 250 hours, I still think something is going to happen, especially since there are so many more moving parts than in a fixed-wing aircraft. Perhaps someday I will get more comfortable, but for now I am always in the “ready” mode.

Being in the ready mode came into play recently with the Hummingbird, and I got to experience firsthand why one should not trust the aircraft until the 100-hour mark. In a couple of prior columns, I shared with you the flight-testing program that I was doing on my recently finished Hummingbird helicopter. It took all the required 40 hours. Even after the completion, I still approached every flight with caution.

It never bit me during the flight test program, although I was continuing to tweak some blade tracking and balancing to smooth out the cyclic stick gyrations. They were more of an annoyance than a problem. I didn’t find any adverse characteristics of the Hummingbird during Phase I, so I dutifully signed off Phase I as completed.

Carol and I decided to go to Peach State Aerodrome for lunch one day, as it’s our favorite fly-to restaurant. The Hummingbird now had 48 hours on it, and I had all maintenance up to snuff. The startup, rotor engagement, and pre-takeoff checks were all normal.

One of the practices I still do is to taxi out to the center of the runway for every takeoff. Yes, it’s a helicopter, and I could just lift off from my backyard, but why not stack the cards in my favor? The runway is almost 200 feet wide. We also had some newly installed RunMat, which makes for a nice, solid grass runway.

As I entered the runway near the centerline and started to pull up on the collective, there was a little shudder in the helicopter and a slight movement of the nose to the right. Carol mentioned afterward that she thought one of the wheels caught the edge of the RunMat. What transpired next happened a whole lot faster than I can tell it.

I glanced down at the engine gauges, and everything looked normal, no different than it had just a few seconds ago when I had completed the run-up. Unlike in a propeller aircraft where we bring the engine back to idle after the run-up, in this helicopter, the run-up is at 3,000 rpm and is left there once completed. Pulling up on the collective from there will bring the rpm up to about 3,200 for liftoff. From the engine data I subsequently downloaded, you could see that I was just starting to bring the collective up, as manifold pressure was at 20 inches.

Suddenly there was a loud noise that seemed like an explosion right behind the firewall, aft of my head. In the next nanosecond, the view out the windshield was a blurry whirl, and the helicopter was spinning rapidly clockwise. I didn’t have time to think. Luckily, the training kicked in, and I went full down on the collective, simultaneously rolling the throttle off and rapidly extending my left leg on the left anti-torque pedal, all the while stepping as hard as I could on the left brake. Everything came to a stop in about one-and-a-half turns — and we were still upright.

It was time to get off the runway, but as soon as I added any power, there was no directional control. I knew immediately what the problem was, so I proceeded to shut it down. Upon exiting the helicopter, I noticed some damage to the right-side cowling, which seemed weird. I figured I had lost the tail rotor. When I tried to turn the tail rotor, it was jammed, so I figured I had a gearbox failure. A quick look at the fluid levels in both tail rotor gearboxes showed they were still filled to the proper levels.

Once we got the helicopter into the hangar and I looked inside the engine compartment, the cause was clear. The tail rotor shaft had sheared a few inches aft of where it connects to the main transmission. When it happened, the now free-wheeling shaft was unbalanced and bent. On its last rotation, the bent shaft slammed into the top of the tail cone mount tube and came to a sudden stop. That was the source of the loud bang I heard.

Carol was cool about it. As for me, I will admit I was a little rattled. A couple of seconds later we would have been airborne, and I bet the results would have been different. Sure, my training kicked in, but I think I’m still in that stage where luck is better than skill. In this case, I think two things worked in my favor. The wheels on the Hummingbird, coupled with the newly installed RunMat, allowed it to spin easily. I think if it was on skids, it may have rolled over. Another good thing is that it happened at home, so repairs were going to be much easier.

After carefully pulling the cowlings off and checking over the rest of the helicopter, I found no other damage other than the sheared shaft and some ancillary damage it caused to the cowlings. Some filler and paint would take care of those. The bigger question was “Why?”

I like playing detective. At one time, I even wanted to be an aviation accident investigator. I think those same skills are pertinent when doing maintenance. In this case, it was a brand-new helicopter. Most of the parts — especially the drivetrain, gearboxes, etc. — had FAA/PMA stickers on them. I soon discovered a crack right at the shear point of the shaft that emanated from the taper pinhole. The gears at each end of the shaft are brazed on at the factory, and the shaft is drilled at that point for the taper pin.

Of course, I immediately called Brad Clark at Vertical Aviation and explained everything to him. As usual, his caring and responsiveness came through in spades. I shipped the part to him for diagnosis and continued to disassemble the related systems to check for any other damage.

Interestingly, I noticed something different while disassembling the sheared drive shaft from the tail rotor intermediate gearbox and the forward main transmission. At the tail rotor gearbox, the gear on the shaft moved freely in and out of the gear on the gearbox. On the other end, it was a snug fit, and I had to use some force to remove it. I videoed the difference and sent it to Brad the next morning, which was a Sunday. Brad answered almost immediately. His dedication showed as he was at the shop on a Sunday morning.

Brad figured it out in short order. The gears were properly made to spec, but in some cases the plating on the gears was a little thicker, thereby causing a tight fit. There is supposed to be a slip fit movement, as the tail boom does flex a little and the gears need to move freely in and out. The gears are also greased for this reason.

This lack of movement created stress on the connection, causing eventual fatigue cracks at 48 hours of flight time. While inspecting his stock of parts, less than 5 percent were found to have a combination of plating that caused an interference fit. This has never happened in 33 years of selling Hummingbirds. It felt good that the smoking gun was found quickly.

In true form that I have seen throughout the build process from Brad, he sent all new parts from the main transmission to the tail rotor (even blades, which are currently being painted as I write this). He rebuilt the transmissions and verified no internal damage. With a sudden stoppage like that, it is best to be cautious. He has also sent out a service letter to the customer base with instructions on how to check for movement in the shaft.

So, has it dampened my enthusiasm for the Hummingbird? Absolutely not. The fun factor is still alive, and Carol and I have had many trips to lunch in it since this event. The factory support has been stellar, and I’m now closing in on another 20 hours since the event. At the time of writing this, I am preparing to leave for EAA AirVenture Oshkosh 2023 in two weeks.

Brad has even flown in it and continues to let me use his Chadwick-Helmuth balance to improve the blade tracking. Both Brad and I think that if this helicopter had been assembled at the factory, it would have been caught. A step has been added to the assembly manual to assure these parts have a slip fit after applying the grease and parts are checked for proper slip fit before shipment.

I’m still cautious about the first 100 hours, but confident. Did I tell you helicopters are addictive?

Vic Syracuse, EAA Lifetime 180848, is a commercial pilot, A&P/IA mechanic, DAR, and EAA flight advisor and technical counselor. He has built 11 aircraft and has logged more than 10,000 hours in 74 different types. Vic founded Base Leg Aviation, has authored books on maintenance and prebuy inspections, and posts videos weekly on his YouTube channel. He also volunteers as a Young Eagles pilot.