One More Engine and a Team of Mechanics

monkey

We’ll just tweak it a little…

There are people out there who build their own planes in their garages, basements, and occasionally even on airport grounds. My friend Ariel is building one in a shed on his property. My friend Dean wrote an essay about it which is buried in the Internet Wayback machine.

I can tighten a screw. I have built a computer, several. I have installed hard drives, memory modules, graphic cards and even replaced a power supply. I have even built a house or two with my own two hands and was able to do everything, frame, run flooring, roofing, decking, install windows, hang sheetrock, wire the electrical… really everything except plumbing (a dark art) or finish sheetrock (those guys are masochists). But I am really not at all mechanical.

When I was up at Friday Harbor a few weeks ago and started the engines for a quick flight with my parents the RIGHT COOLANT warning lit up. That would have been the end of the visit for me, I would have had to find a shop that could fly someone out to the island to figure it out. My brother took the cowling off the engine, found the clamp that had loosened a little bit, tightened it, found the proper coolant in his garage, refilled the reservoir and watched me takeoff for a test flight. He poked around the engine (which to me always seems amazingly clean) and said, “You can see the white spray of the leaking coolant, you can smell it, too. That’s the sweet smell.” I couldn’t smell anything.

I would love to have that skill set, those instincts. Come the apocalypse I just hope there’s a need for someone that can drive a nail through a couple boards while only hitting his thumb once or twice.

They made aircraft mechanics so that pilots have someone to look up to.

One of the reasons I am so comfortable in the air, so confident in the machine that bears us up to the cruise altitude two miles above the earth, is that I trust the guys that work on it. Dave Seastead and his crew have been taking care of N971RD and N972RD for over half a decade. When I talked to Nell about owning our own plane I pointed out that when we rented a plane we had no idea what maintenance items the operators were postponing, or still in the middle of chasing. Our first family flight (up to Fresno, for Thanksgiving dinner in Yosemite) included the malfunction of the push-to-talk switch on the pilot’s yoke. So I spent the flight reaching over and using the button on Nell’s yoke, with our headsets cross-wired in the plugs. I later found out that it had been up to the shop four times with that same complaint. If I owned the plane I would have replaced the button.

You want a shop that is not so expensive that you hesitate to bring them a problem. Finding a problem can take a visit or two if it is intermittent. You want a mechanic who really cares about what they are working on, who doesn’t push the blame off on mechanics who have previously worked on the plane or the engineers who designed it. Both are convenient, since neither can be perfect, and sometimes work needs to be done to correct the original design and work that someone did when you were away from home.

Ideally, you want a mechanic who understands your concerns, who knows that a five hour flight with the family is a different endeavor than your usual hop up to Camarillo for lunch. And who knows things that are long range worries versus things that you need to make perfect before you can happily take to the sky again.

For us, that has been Angel City Flyers’ MX Aero shop.

On the way out of Friday Harbor, the trip after the coolant was fixed, I heard the “bong” noise that means the G1000 has detected a fault somewhere. There are a lot of electronics, a lot of sensors, and the two engines. The electrical system is complex all by itself. I had heard a bong on departure from Santa Monica, but there was nothing on display and it was only the one. This time I saw a flash of the red text that usually comes up for a warning. Then it bonged again. I was climbing over the cold waters of the Pacific that course through the channels around the San Juan Islands. I multi-tasked a little, contacting Air Traffic Control, setting up the autopilot, and texting back to Adam to see if he could remember the place we had landed back on the mainland where they had a shop that did Diamond maintenance. Then I spotted the text: “L GEARBOX TEMP.” Okay, that’s something to think about.

The plane climbed up through the clouds. My parents were talking about the houses they could see along the shore of San Juan Island, and snapping photos. ATC wanted a report on my altitude and I flipped to the pages on the MFD that showed the gearbox temperature. I took a little video shows the behavior: the temperature is steady but it flips up into the red sort of randomly.

I pictured what the sensor was there for: the engine, like all internal combustion engines, has to spin fast to be efficient. It has to spin at near four thousand revolutions per minute. The explosion of gases in the cylinder is fast, trying to slow the motion it produces is impossible, you have to go with the flow. But if you spin the propeller at those speeds then a portion of the blade would be going faster than sound, making the air around the blade turbulent in ways that would make them inefficient. So there’s a gearbox to reduce the engine RPMs to propeller RPMs that make sense (2,100 is nice). The gearbox is a mesh of high-strength steel gears, axles, and things spinning really fast in really close tolerances. There’s friction. Things get hot. So you run oil through it to keep it cool. If something goes wrong that oil will get hot, that’s what the sensor is checking.

There’s no way the oil could be jumping in temperature the way the sensor was reporting. So either bad sensor, bad computer (software), or bad wires. The last seemed least likely, since a bad wire should just show temperature: none. Since I had determined it was a spurious warning, we flew on. I knew that if it was a real problem, I could shut down that engine and fly to the field that Adam had texted me the identifier for (KBVS and the friendly folks at Corporate Air Center). We buzzed along over the Pacific and had a great flight down to Santa Monica.

I reported the issue to Dave and they swapped the sensor between the two engines. That way if it was a bad sensor it would show up as the right engine’s gearbox temperature instead. No such luck. Dave said that the wires that run to the sensors sometimes get heat damaged or vibrated to bits. The left engine has a thousand hours on it, so that seemed possible. Since it would most likely be the connection to the sensor, or half a foot back from there, Dave clipped the wire, re-wired to the sensor and I flew some more. Intermittently, I still got the annoying “bong,” and the warning. Even knowing it was spurious, the warning was a bother.

At the 100hr service and oil change they cut the wire back a lot further. To troubleshoot more than that would require unwrapping a lot of the wire harness where all the sensor wires were gathered, dozens of them made up a package that was as thick as my thumb and ran back along the top of the engine, down through a protected hole in the firewall and to the Engine Control Unit below.

I still got the error. Since a long family trip was coming up I wanted them to find the problem and Dave said they could look at it Thursday morning. I flew down (ILS approach to three-zero) and wandered off to sit in their WiFi and air conditioning while they tore open the wiring harness. About an hour later, Dave sent me a photo. Just before they were going to sort of give up and cut it back another ten inches and hope they got it, he lifted up a portion and saw the issue.

splice

“Might be a good spot for a splice.”

It is hot in an engine compartment. There is a lot of vibration. There are a lot of sharp edges. So as you run wires around to the various sensors and sources, you make choices about whether to run it alongside the hot exhaust riser or over the top of a structure piece that has some sharp edges. The wiring harness, a bundle of two dozen wires, ran across the top of the engine. There was one spot where it cross the edge of a structural support. Over time (a thousand hours of the engine running), the vibration of the engine and the tension of the bundle of wires let the edge cut through the insulation of the one wire, not all the way, just sort of rubbing its way through to touch on occasion. Just when the engine was vibrating at exactly the right frequency, it would ground the wire for an instant. Just long enough to make the sensor register some crazy number way up the scale.

bite

Sharp

Aircraft are like any other human endeavor in the engineering and manufacturing space. The final item is a product of the engineer’s and designer’s choices. For it to function in the real world it sometimes needs modifications by the people who see it operating day to day. The engines come from the factory with a lot of colorful heat-proof tape wrapping the wiring harnesses. But you can see the metal edge and you can picture how it would slowly worry its way through the insulation and protection on the harness.

fix

Bulletproof

In the real world, zip ties keep things where they are meant to be inside the engine compartment. And if you look at Stan’s fix you can see that the wire tires are holding another piece of (blue) protection between that sharp edge and the bundle of wires. Another thousand hours and the same problem will not crop up.

There will be different problems. There always are. The new plane is amazing because it is so advanced, but it is a collection of complex systems and increased complexity means there is an increase of failure points. When I am confidently humming along at ten thousand five hundred feet, with the autopilot making a turn over Fresno to point the plane at Redding, and all three of my passengers are asleep, my lack of anxiety is directly related to these guys and the hard work they do to keep us safe.

heroes

Heroes

When I was watching them work on the oil change some of it looked like things I could do (dump oil out, pour oil in, tighten a screw). I know that under the FAA’s regulations, I am allowed to do my own oil change. So I said to Dave, “If I learned how to do a few of those other things than I could do this myself, right?” He looked back and forth from where he mechanic was fiddling with some arcane portion of the engine and to me. “Yeah, you could… but then you’d have super powers.”

I’m not foolish enough to think that they will never make a mistake. Humans are fallible. But they haven’t made many in the more than five years they have been turning wrenches on our planes, and when they have they’ve jumped in to correct things.

About Colin Summers

I am an architect, programmer, private pilot, husband and father. A couple of those I am good at.
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One Response to One More Engine and a Team of Mechanics

  1. Ron Rapp says:

    Pilots (and owners) often dump on mechanics for their failings, but as you said, they do a tough job — often in agonizingly uncomfortable settings — and usually get it right. When I worked at Dynamic Aviation’s SLI base, most of the pilots who flew the U-21As were also mechanics. Talented and hard working guys. I gained a lot of respect for the A&P by watching them work. Today very few people know how to repair things. Replace components? Sure. But the craftsmanship that comes with being able to actually repair them is something I highly respect.

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