The Cross-Country Capable Cessna 310

The Cross-Country Capable Cessna 310

A 310 owner reveals what ownership of a twin Cessna is really like.

The Cessna 310 was the first twin-engine aircraft produced by Cessna after World War II. The 310 prototype, powered by 240 hp Continental O-470-B engines, first flew Jan. 3, 1953. The aircraft was certified March 22, 1954. Production began immediately and continued through 1980. 

A September 1954 Flying cover story introduced the 310 to the masses with the headline, “Business Asked for It,” written by Cessna Aircraft Company president Dwane L. Wallace. Wallace cited the popularity of military surplus conversions as an indicator of the strong need for a purpose-built twin for the business flyer. He opined that “[when] properly used, [aircraft] are, without question, REAL BUSINESS TOOLS.” 

Cessna’s advertisements of the day claimed the 310 was “at least five years ahead in design and engineering,” and that “it looks and is smart and fast.” 

As for the size of the market for a new business-class twin? Wallace’s writing was prescient. “It may seem difficult to predict the future of the twin-engine market. I do know that the need is almost unlimited and, knowing the American way of doing business, I make the assumption that therefore the market is practically unlimited.”

Over the next three decades, his words rang true. A total of 5,449 Cessna 310s were produced from 1954 to 1980. They were not just business airplanes; they were TV stars, too. The Cessna 310 (a B model and D model) had a prominent role in the popular “Sky King” TV series (also a radio show) of the 1950s. 

Nowadays, the Cessna 310 isn’t the fastest airplane on the ramp, nor is it the most economical to own and operate. Many of the early 310s are no longer with us, and those that are still around are often “put out to pasture,” tied down in a far corner of the airport, surrounded by cracked asphalt or overgrown grass. 

However, some of these classic twins have been saved from a slow melt into the tarmac. Gale Cawley rescued his 1965 Cessna 310J from a miserable fate in the spring of 2002. 

Gale isn’t quite the 310 owner that Dwane Wallace had envisioned a half-century prior, as Gale had no desire to operate the airplane for business. Instead, he wanted a personal touring aircraft which would increase his three-hour-flight range. The 310 offered impressive speed and useful load for a low initial acquisition cost. He knew that it wouldn’t be the cheapest to keep in the air, but he believed the cross-country capabilities of the aircraft would offset the ongoing costs.

The 310 lived up to Gale’s expectations. His home base of South Haven Area Regional Airport (KLWA) in southwest Michigan provided a jumping-off point for flights around the United States. He owned the aircraft for 15 years before selling it to a friend.

Gale said he also wanted the 310 because, frankly, it was a cool airplane. He recounted listening to the old “Sky King” radio shows a half-century earlier. Young Gale would have likely been thrilled to know that after an extensive Air Force and airline career, he would acquire a Cessna 310 and fly it, Sky King-style, to his friend’s cattle ranch in rural Oregon! 

A Cessna 310I model, similar to Gale Cawley’s 310J, shows off its sleek lines and wingtip-mounted fuel tanks.
Cessna Flyer’s Scott Kinney had a chance to talk with Gale about what he learned from owning and flying the 310.

Q: What sort of shape was your 310 in when you acquired it?

It had lived, I’ll say, a bit of a rough life. It was delivered new to the U.S. Air Force in 1965. The civilian logs started in 1975. It had about 4,000 hours on the airframe when I bought it. The guy I got it from was a businessman. He’d used the 310 to scout for new franchise sites around the country. 

The airplane had been the subject of some drama in the years before I bought it. It had been held as evidence without flying for three years. There had been some sort of legal dispute over an annual inspection bill… the bill was something like a hundred thousand dollars. Once that finally got cleared up, it was on the market for another year before I bought it. 

I made the guy an offer that I thought was pretty low. He accepted, as he was happy to be done with it. I figured I’d gotten the 310 for a good price, so maybe wasn’t as diligent as I should’ve been with the pre-buy.

I wasn’t surprised that it was a project… turns out, though, it was a real fixer-upper! 

The left engine was run out. The right engine wasn’t timed out, but I didn’t have much confidence in it. Both props were high-time. As far as the avionics, they weren’t much better. The airplane had a dated panel with old radios. 

Q: Where do you begin with a project like that?

In the first year, I had both 260 hp Continental IO-470-D engines overhauled. The left engine was overhauled and installed by G&N Aircraft. Poplar Grove did the right engine. 

A pair of 260 hp Continental IO-470-D engines provide good performance.

So, why did I use two different shops? Well, I sent the 310’s left engine to G&N as it needed to be done immediately. They’d overhauled my Cessna 210’s IO-520 engine a few years prior. They used chrome cylinders on that one, and I had them do the same with the 310’s left engine. 

Not long after I’d had the left engine overhauled, I started having trouble with the chrome cylinders in the 210. 

I had the 310’s right engine overhauled several months after the left.

I did a little more research and found that the big Continentals didn’t do well with chrome cylinders. I also read more about other shops and saw that Poplar Grove was one of the best in the country. I decided to give Poplar Grove a try and had them use steel cylinders.

Both shops did good work. I had no trouble with either engine during my 15 years of ownership. 

I sent the props off to Tiffin Aire. They called me and asked me if I was sitting down. I knew that the props were high-time, but as Tiffin explained, there had been some “creative” record keeping in the past, and the serial numbers of the blades didn’t match the logs. Without proper records, the props were junk, and went into the dumpster. I bought new three-blade Hartzell props from Tiffin Aire.

Avionics followed shortly afterward. In addition to a much-needed radio update, I replaced the old Loran with a [Bendix King] KLN 89B GPS, and I put in a modern S-Tec 50 autopilot. I also had the instruments rearranged into a basic T configuration. Joliet Avionics (now J.A. Air Center) did the work. 

Many 310s have had avionics work done over the years.

I had a very thorough first annual and made sure everything was checked, including control rigging—pullies, cables and so on.

As all of this was getting done, I went to Flight Safety in Wichita, Kansas, to get some simulator training to make sure I was ready to fly the 310 when the work was complete. 

Q: That’s a lot of work! 

Yes, and it was not cheap, but it was well worth it. By the time all of that was done, I had a great “Sky King” airplane that flew very well. 

Q: How did it perform?

I could go fast, but that cost a lot of fuel. Depending on power settings, I saw fuel burns between 22 and 28 gph. 

I babied the engines and didn’t use more than 60–65 percent power for most flights. I liked a combination of 23 inches map and 2,300 rpm. The 23-squared combination “sang in sync,” and gave me a fuel flow of around 25 gph.

I consistently saw cruise speeds of between 165 and 170 ktas. 

With a usable fuel capacity of 130 gallons (100 gallons in the mains, 30 gallons in the auxiliary tanks), I had a range of about four hours with a comfortable VFR reserve. 

While the three-bladed props probably didn’t increase cruise speed by too much, they certainly helped with takeoff and climb. They also made for smooth and quiet operation. 

Normally, I flew with the right rear seat out in order to have more baggage space. The baggage door was located on the right side of the fuselage, which gave me easy access to the right rear seat area. 

Q: Did the aircraft have any other modifications?

Yes, it had MicroAero vortex generators (VGs) on the wings and the vertical stabilizer. The VGs provided exceptional stability at the slow end of the envelope. The airplane simply wouldn’t break hard or drop a wing in a stall. It would just go into a very smooth sink. 

The VGs allowed for slightly slower approach and landing speeds if you wanted. I always used the printed book speeds and felt those worked well. I felt that the VGs were a superb addition to the airplane.

Q: Any issues with useful load or center of gravity? 

My 310J was a six-seater, but it was shorter and a few hundeds pounds lighter than later models of the 310. 

The useful load was around 1,700 pounds. I didn’t usually come anywhere close to maximum gross. The majority of my flying was solo.

I took it to Oshkosh one year with all the seats filled and full tanks. That put my takeoff weight close to max gross. It was summer and hot, so the 310 climbed out a little slower, but it handled it well. 

Setting elevator trim correctly was very important. Whether taking off with just myself or six people in the airplane, a trim setting close to the “takeoff” mark worked well. The direction (up or down) from the mark depended on the load. When I flew alone, the aircraft was a little nose-heavy, but it wasn’t hard to compensate for that with a slight up trim setting. Q: Were there any operational quirks that you noticed?

A few. Preflights were mostly straightforward, but you needed to be careful when you were under the right wing. There’s a speed vane, which runs the Hobbs meter, on the bottom of the wing. It’s a little tab that sticks out. When air flows over it, it compresses and touches an electrical contact, activating the meter. It’s possible to accidentally snag [the tab] and bend the vane. I did, and that prompted me to get my mechanic to fix it. He placed small protective rails on each side of the vane, so it would still get airflow but wouldn’t catch on loose clothing if you brushed against it.

Fuel management was a little different, too. I learned not to fuel the main (wingtip) tanks all the way to the filler caps. If you did, fuel would siphon out the vents as your speed increased on the takeoff roll. 

The auxiliary tanks had their own peculiar features. If you select the auxiliary tanks, the engine-driven fuel pump draws from these tanks. However, the pump draws more fuel than the engines burn. The excess is pumped back into the main tanks (not, as you might assume, into the auxiliary tanks). So, even though you were burning, say, 13 to 14 gph with each engine, you could draw down the two 15-gallon auxiliary tanks in about 45 minutes. The main tank quantities would increase slightly. 

There’s another thing about the auxiliary tanks which could cause an “uh-oh” moment if you weren’t expecting it. When the airplane was cruising and hit slight turbulence, it had a tendency to yaw. When the auxiliary tanks were low, the yaw would push fuel away from the fuel intake, and the engines would sputter. The answer to this phenomenon was to either ride a rudder to stabilize the swaying or to switch back to the mains when turbulence was expected.

Another surprise was that the Janitrol cabin heater would not work unless the proper air vents to the cabin were opened. I learned this one the hard way, and had a very chilly flight!

Q: Did you operate your engines rich or lean of peak?

I only had single-cylinder EGT gauges on each engine. I ran the engines rich of peak. I figured burning just a tad more fuel was, in the long run, less expensive. I didn’t like the idea of replacing valves or cylinders if I ran them too hot. 

Q: Speaking of replacing things, how were your maintenance costs?

I had most of my work done at a Cessna-certified shop—Michigan Aviation in Pontiac, Michigan. My basic annual inspection ran about $3,600 on average. Any extra work cost more, of course. I really tried to keep up on the maintenance. I feel that good maintenance is cheap life insurance. I live in an area where hangars and other fixed costs are low, and that allowed me to spend money on quality work.

There were a few surprises during the 15 years I owned the aircraft. On this particular model of Cessna 310, the rear wing spars are vulnerable to corrosion from exhaust gases. I learned about this firsthand as I had to replace the left rear wing spar. That was a $10,000 bill. I had the work done at TAS Aviation in Defiance, Ohio. They specialize in twin Cessnas and 310s.

Q: Any other thoughts on the 310?

It was a wonderful cross-country airplane. It took me so many places: to visit my son in Connecticut, my friends in Arizona, my daughters in South Carolina and my siblings in Kansas City. I used it exclusively as a personal aircraft. I put around 400 hours on it during my ownership.

It was also not as expensive as you might think. I found the overall cost to run the 310 was about 40 percent more than my Cessna 210. 

A friend of mine talked me into selling him the 310 last year. He’s put over a hundred hours on it in the last eight months. He’s taken it around the country as well as to the Caribbean and Mexico. In retrospect, it may have been my loss and his gain!

Gale Cawley earned his private pilot certificate in 1960 at Stockert Flying Service in South Bend, Indiana. Since then, he’s flown for the U.S. Air Force, the Indiana Air National Guard and spent 33 years with American Airlines. He holds ATP, flight engineer and CFII certificates and has logged over 26,000 hours. In addition to the Cessna 310 and 210, Gale owned a farm airstrip of his own for 14 years. Scott Kinney is a self-described aviation geek (#avgeek), private pilot and instructor (CFI-Sport, AGI). He is associate editor for Cessna Flyer. Scott and his partner Julia are based in Eugene, Oregon. They are often found buzzing around the West in their vintage airplane. Send questions or comments to .



Poplar Grove Airmotive
Micro AeroDynamics Inc.


G&N Aircraft Inc.
J.A. Air Center (formerly Joliet Avionics)
Michigan Aviation
TAS Aviation Inc.
Tiffin Aire Inc.


FlightSafety International


Jennifer Dellenbusch, “310 Tale,” 
Cessna Flyer, August 2012. 
Dwane Wallace, “Business asked for it: The story of the new Cessna 310,” 
Flying, September 1954.
Magneto Maintenance 101

Magneto Maintenance 101

Understanding magnetos and manufacturer recommendations for maintenance can help ensure your safety. 

The following is an excerpt from Bill Ross’ book “Engine Management 101.” Published by Superior Air Parts Inc., this book is a compilation of what Bill has learned during his 35-plus years of experience as a pilot, aircraft owner, piston aircraft engine industry leader and FAA A&P/IA.

Although the basic magneto has provided very reliable service to aircraft operators for over 100 years, it’s still a very misunderstood part of your engine. For example, while many owner-pilots think it needs the aircraft’s battery to operate, the fact is your magneto is a self-contained unit capable of full functionality that is independent of the aircraft’s electrical system. 

There is no battery power required to start or sustain an aircraft magneto operation. Oh, there are a few that would say, “Without the battery (to turn the starter), the magneto is not able to function.” 

Obviously, they did not grow up on our airport in South Alabama where hand propping was the normal procedure. Many of the aircraft that I cut my proverbial pilot’s teeth on had, and still have, no electrical system. Therefore, the only way to start the engine was the “Armstrong Method.”

The basic aircraft magneto uses a strong rotating magnet inside a coil. There is a voltage produced in this primary coil, which is then stepped up even higher in a secondary coil. This is achieved by having more windings in the secondary coil than in the primary. The increase in voltage is enough to excite the spark plugs to then spark-ignite the fuel/air mixture for combustion. 

While the magneto is very reliable and robust, it is intolerant of neglect or abuse. This article is not intended to make you an expert on magneto theory, function and maintenance but should prove helpful in understanding the periodic maintenance recommendations by the respective manufacturers. As pilots and owners, if we understand these recommendations and why they are important to safety, we can ensure our maintenance provider is correctly following them.

Understanding the mag check

The magneto check is one of the first things we learn as student pilots. Run the engine up to a specific rpm and switch to the right mag, then the left. If you see a “suitable” drop in the engine’s rpm, you’re good to go. Or are you? 

One of my first jobs as a pilot (besides flight instruction) was flying charter in various piston-powered aircraft. Oftentimes, we were paired with another pilot because we had a contract with the Army Corps of Engineers, and the rules required two pilots even if we were in a Beech Baron with a single yoke.

We had another pilot on our staff named Charlie. Charlie and I flew a lot together, and he taught me a lot about flying and engine operations. He was in the first class of flying sergeants to graduate from Columbus, Mississippi, during the onset of World War II. 

During his career, he flew B-25 bombers and then had a 34-year career as a captain with Pan Am. Anyway, early on in our flying partnership, he told me the funniest story about magneto checks. When he was in primary training and just about ready to solo the Stearman, he would watch the instructor reach up and move the ignition switch back and forth and notice a little rpm drop on the engine. 

For each and every flight, he would watch in confusion as to why the instructor went through this ritual. Was it superstition, an ode to the flying spirits, or nervousness on the part of the instructor? Whatever the reason, our friend Charlie had no idea why the Army Air Corps instructor repeated this odd ritual. 

So when it came time for him to solo, Charlie reached up and did the same pre-takeoff ignition ritual as the instructor. 

It wasn’t until after he soloed that his instructor covered magneto checks in ground school. Remember, this was a civilian/government contractor after all, and well, sometimes they do things a bit odd.

The point here is even today, with all the information available about runup mag checks, do we still get caught up in the ritual and not really look at the health of the ignition system as a whole? No doubt we all do.


Magneto internals at 500-plus hours. These magnetos checked OK in runup.
Does the mag drop really mean anything?

After many years and thousands of hours in the left seat, I’ve learned that simply having an “acceptable magneto drop” during engine runup is not necessarily a good indicator of the overall health of your magneto system. Even if the drop is only 50 rpm, there are many issues that could well be lurking inside the magneto that are just waiting to come out and cause problems. 

During my career as an A&P, I have personally performed analytical inspections on many engines that were destroyed due to improper, or an overall lack of, magneto maintenance. 

Yes, I know there are many “experts” in the General Aviation industry professing that you can learn everything about the health of your magneto by simply performing a lean of peak test while in flight. 

I also hear a lot of talk about how today’s sophisticated engine monitors are capable of detecting imminent ignition system issues. While to some degree this can be true—such as determining spark plug performance, spark plug lead and minor magneto issues—even the best engine monitor is not capable of predicting the future. 

Contrary to the opinions of many, a lean of peak magneto test or engine monitor cannot predict some of the serious issues I have witnessed with ignition systems. These include worn or fractured gear teeth, lubrication distress, cracked housings—the list goes on and on. While a magneto problem may not seem too serious, believe me, it can be disastrous. 

Magnetos need maintenance, too

There are very specific maintenance checks recommended by the manufacturer that are extremely important to both the safety and reliability of the engine and aircraft.

The problem is most aircraft owners, and some mechanics, are not aware that these recommendations even exist. For example, manufacturers of both the Bendix-style and Slick magnetos “recommend” a 500-hour inspection for their units. 

Personally, I know very few owners that actually know of, and fewer who actually comply with, this recommendation. 

“It’s only a recommendation,” they’ll say. Well, that’s true. But these are often the owners who are plagued with difficult starts, a rough-running engine and an ongoing list of other unscheduled maintenance practices. Remember, the purpose of scheduled maintenance is to prevent unscheduled maintenance.

In addition, Bendix-style magnetos have a recommended four-year-in-service or five-year-from-date-of-manufacture replacement/overhaul, whichever occurs first. 

Therefore, if a Bendix-style magneto has been on the shelf for three years and is then installed on an engine, it only has two-year useful life remaining before recommended overhaul. Again, this is a recommendation, but following it can be beneficial to ensure system reliability and flight safety. 

Why do these particular units have this type of recommendation? Magnetos that sit on the shelf can be severely damaged by corrosive attack due to inactivity. Conversely, magnetos that have been in service for a period of time can become worn due to contamination and operation. Magnetos that house excessive dirt and electrolytic debris are prime candidates to ruin your day.

Oh, they may check fine on the ground during runup, but they may well have internal issues that will show up during your flight. Some scenarios could be cross-tracking of the spark within the distributor block. If the spark reaches the incorrect pole, a preignition event can occur leading to detonation and engine failure. Cracks in the distributor drive gear can lead to fracture of the gear and stop the distribution of spark to different cylinders. 

Over the years I have performed several analytical inspections pertaining to preignition/detonation events that exhibited fractured away teeth on the distributor gear. Once the gear could no longer be driven, the distributor finger would fire only on one cylinder. This leads to a preignition/detonation event and destroying the engine. 

Even though I wish they could, engine monitors cannot predict events like these. Like with many parts of your aircraft and engine, the only way to help keep issues like these from ruining your day is to follow manufacturer’s recommended maintenance, inspection and replacement intervals.

Keeping your magneto healthy

Think about it: We routinely change oil in the engine, but we don’t change oil in our magnetos even though the manufacturer says we should. Why is that? 

During the typical 500-hour engine inspection, the maintenance provider should disassemble, clean and inspect the magneto internal parts. At the same time, the breaker points and condenser are normally replaced and the magneto is lubricated. Inspection of the gears for cracks or abnormal wear is very important to the function of the magneto and health of the engine.

In addition, the impulse coupling (if equipped) is inspected for excessive wear and correct functionality. The impulse couplings are a spring-loaded component that aids in engine starting by accelerating the rotating magnet and retarding the timing. 

Having an impulse coupling that is not functioning properly can lead to the engine firing in full advance timing and thus lead to a kickback during starting. Kickbacks can wreck your starter and severely damage engine components. 

After inspection, the magneto is reassembled, tested and installed back on the engine. Next, the magneto-to-engine timing is set in accordance with the engine manufacturer’s instructions and specifications. 

The best advice to help you get the most out of your engines and components is to simply follow the manufacturer’s recommendations for continued airworthiness.


Bill Ross is a graduate from the University of South Alabama and was employed by Continental Motors for 15 years holding positions in engineering, analytical, air safety and technical product support. Ross is now Vice President of Product Support for Superior Air Parts and committed to the company goal of making flying affordable. When not working at Superior, Ross can be often found flying his family’s 1941 Boeing Stearman, working on antique aircraft or exposing young people to the joys of flight and potential careers in aviation. Send questions or comments to .

Off to a Good Start: Planning for your First Annual

Off to a Good Start: Planning for your First Annual


Evaluate and maintain a new-to-you aircraft using all of the tools available today.

So, it’s been a year since the pre-purchase/annual inspection was completed and you have been the owner of this new-to-you airplane. As the months passed, every flight revealed more details about the condition and usefulness of your new flying partner. 

You probably encountered a few issues that required immediate attention and many others that became line items on your to-do/wish list. (In last month’s Cessna Flyer, Dennis Wolter outlined best practices for preparing to tackle a renovation. —Ed.)

With this list and your maintenance technician’s familiarity with your new airplane, the arrival of annual inspection time presents the perfect opportunity to sit down with your mechanic and put together a schedule for the renovation of your airplane.

In the list that you put together when flying the airplane during previous months, it’s important to include maintenance and performance issues that need to be discussed before starting that all-important first annual. 

I definitely believe that you should read all applicable Airworthiness Directives and Service Bulletins and confirm that important issues are well-understood and properly completed. Just because an AD is signed off in the logbook doesn’t mean that it was done properly or even that it was done at all. A couple of times a year at Air Mod, we find evidence that a signed-off AD was, in fact, never taken care of. 

The point here is that between a thorough pre-purchase and the first annual, all issues are checked and verified, and your airplane should be off to a good start toward working its way to being a “good as new” machine.

From a safety standpoint, the condition of your airplane’s engine is of major importance. You should take advantage of every technical process available for evaluation and maintenance in this area. 

Back in the day, inspecting an oil filter for contaminates such as metal particles and performing a simple compression check were the two major engine evaluation processes that a technician used in determining the health of the piston engine.

Compared to my early days in this industry, we now have at our disposal far more inspection and diagnostic tools that make it possible to operate our engines longer with greater confidence. 

Determining engine health

A compression check is done to determine the health of the upper or power section of the engine where combustion takes place. Combustion exposes pistons, rings, cylinder walls, valves and valve guides to a lot of heat and combustion byproducts. 

The time-tested compression check involves a technician using compressed air and air pressure gauges to determine if the cylinder and all of its parts are doing the job of sealing in the combustion gases in such a way as to efficiently produce the desired pressure of pushing the piston down to turn the crankshaft and rotate the propeller. Any leaking of these high-temperature gases past the valves or the piston and ring assemblies will cause heat buildup, a decrease in engine performance and increased wear on these critical components. 

As good as the compression check was and is, it falls short of presenting all the information needed to fully evaluate the condition of the combustion components of a piston engine.

Beam-me-up-Scotty to 2018. Today, we have three diagnostic tools that bring engine condition tracking to a whole new level. 

Tool No. 1: Borescopes

The first implement I refer to here is the affordable, state-of-the art borescope. What’s that, you might ask? It is a 1/2-inch diameter, 18-inch-long fiber-optic tube that can be placed in an engine cylinder through a spark plug hole. It will present a high-resolution color-correct image on a bright screen that allows a technician to evaluate the condition of the cylinder walls, piston crown, valves, etc. 


Borescope being placed in an engine cylinder.

Often, an engine that has good compression will have stress marks on the cylinder walls or discoloration on valves that can only be seen with a borescope. These anomalies can indicate a potential for future problems. The borescope allows a technician to address an issue before it becomes a failure. Also, most borescopes have a built-in digital camera, making it easy to email a picture of a problem to the customer. So much for the good old days!

Here is a great example of the value of this technology. I called a good friend, Adrian Eichhorn, who has done quite a bit of research into the use of this technology, to help identify cylinder components that are in the early stages of failure. He sent me a photograph of an exhaust valve that presented an uneven color pattern, indicating that the valve was becoming too hot in one area and not sealing at that point on the edge of the valve. 


Uneven color pattern on an exhaust valve indicates a possible problem.

If not corrected, the valve will eventually begin to deform and lead to serious and expensive valve failure. Eichhorn, in partnership with AOPA, came up with a chart showing various color patterns that indicate different types of potential valve failures. These charts have been distributed and used in the field with very positive results. Smart! (A link to the PDF and other information referenced in this article can be found below —Ed.)

These borescopes are miracle investigative tools that allow technicians to see into inaccessible areas in various parts of the engine and airframe. I have a customer who recently used one to find a badly-corroded elevator component that was close to failure.

Tool No. 2: Oil analysis

Another important area to be evaluated is the bottom end of the engine—the crankshaft, connecting rods, oil pump, camshaft, etc. Back in the good old days, about the only diagnostic tool a technician had to help establish the condition of these components and their bearings was to hold a magnet in the oil as it drained out of the engine and look for magnetic or ferrous metal particles sticking to it. A technician could also cut open the full-flow oil filter, if the engine was equipped with one, and look for metal fragments in the filter. 

Magnetic fragments mean a steel component is experiencing high wear; nonmagnetic fragments mean a nonmagnetic component such as a bushing is wearing, or something is rubbing the aluminum crankcase. Fragments don’t always provide enough information to accurately diagnose a potential problem. Big pieces of metal indicate serious pre-failure issues.

The second engine diagnostic tool I’m going to discuss is oil analysis. It can vastly improve a mechanic’s ability to assess an engine’s health. 

Here’s how it works: as the technician is draining old oil out of the engine, a small cup is filled with an oil sample that is sent to a laboratory for analysis. After testing, the lab returns a report to the technician that indicates the percentage of metal residue found in the oil, measured in parts per million and listed by type of metal. Iron can indicate wear on the oil pump gears; silver can indicate wear on a plain bearing such as connecting rod or crankshaft main bearings; bronze can indicate wear on valve guides, and so on. 

As the engine builds hours and additional oil samples are analyzed, a technician can track data and determine wear trends of the various internal engine components. If a high reading of a specific metal is noticed, the technician can use this information to identify a possible point of failure and initiate the appropriate maintenance action.

Tool No. 3: Engine monitors

The third 21st-century device that has revolutionized the monitoring of piston engine operation and maintenance is the digital engine monitor with data download capability. The complexity of these systems can range from basic exhaust gas and cylinder head temperature monitors to systems that replace existing round engine instruments with a full screen that has multiple additional readouts for voltage, percentage of horsepower, fuel remaining and even outside air temperature. 

These systems allow valuable information to be downloaded and analyzed by an owner, a technician or an online company, to track engine condition trends. Science fiction has become reality. We should take advantage of these contemporary tools to ensure the safe and efficient operation of an engine all the way to TBO. 

Digital engine monitor with data download capability.
Other items to evaluate


An annual inspection item that I believe is sometimes not carefully looked at is the age and condition of the fuel, oil and vacuum flex hoses. Many rubber flex hoses in service today have a service life of five years. Failure of an oil or fuel hose can definitely contribute to a bad day! 

I highly recommend replacement of timed-out hoses with hoses fabricated with cost-effective, safety-enhancing orange fire-resistant sleeves, which protect the hose and its often-flammable contents in the event of an electrical or engine fire. The photo shows a typical black hose with a service life of five years as well as a stainless steel fitting, fire-sleeved silicon rubber, extended service life, top-of-the-line hose. 

Extended service life hose on top, typical black hose below.

Engine accessories

Moving beyond the engine itself, it’s important to monitor the service life and condition of the engine accessories. A good pre-buy inspection should have clarified the times in service and inspection status of all the stuff that keeps the engine running. 

An owner needs to be aware of the status of these components in order to prevent as many surprises as possible.


Let’s focus now on a big item: magnetos. Most brands of magnetos require a 500-hour half-life inspection and a 1,000-hour overhaul or replacement. Experience has shown that scheduled maintenance and monitoring is very effective in increasing the reliability of these critical components. (For more, see “Magneto Maintenance 101” by Bill Ross on Page 32 in this issue. —Ed.)

Vacuum pumps, propeller governors

We know that dry vacuum pumps driving traditional gyros have a higher failure rate after 500 hours of operation. Propeller governors are best overhauled at engine change. The failure of a prop governor can send engine-damaging metal through the engine’s lubrication system—that means big bucks to fix! The point here is to have a meeting with your maintenance tech and totally vet the status of all firewall-forward systems. 

Engine overhauls

OK, I’m walking on thin ice here. No discussion about piston airplane engines would be complete without talking about the often-debated subject of time between overhauls (TBO). It seems like experts are all over the map as to when a seemingly great-running engine should be overhauled. Opinions range from “TBO is cast in stone” to “TBO is an arbitrary, money-making number set by the engine manufacturer.” 

Here’s an 18-year-long anecdotal study I was unintentionally exposed to during the time Air Mod was located next to one of the more active field overhaulers in the country. Located by their hangar were two dumpsters. One contained rejected ferrous metal engine parts (crankshafts, connecting rods, gears, cams, etc.). The other contained rejected nonferrous aluminum parts (crankcases, cylinder heads, etc.). Most of the engines going through their facility were overhauled at or near TBO. 

Based on the quantity of rejected parts that got hauled off to the recycling facility, I tend to think that the manufacturers base TBO numbers on experiences they’ve had tracking these engines for almost a century. Just remember, you can’t write the check on the way down!

If it’s time for you to schedule that engine overhaul, tune in next time as we look at the options and process involved overhauling your trusted engine. Until then, fly safe.

Industrial designer and aviation enthusiast Dennis Wolter is well-known for giving countless seminars and contributing his expertise about all phases of aircraft renovation in various publications. Wolter founded Air Mod in 1973 in order to offer private aircraft owners the same professional, high-quality work then only offered to corporate jet operators. Send questions or comments to .



Electronics International
Insight Instrument Corp.
J.P. Instruments Inc.
“Anatomy of a Valve Failure” under “Magazine Extras”


“My engine is 50 hours from TBO….” by Bill Ross
Cessna Flyer, August 2018
“Is Your Engine Worn Out?” by Steve Ells
Cessna Flyer, October 2017
“Engine Overhauls, Illustrated” by Jacqueline Shipe
Cessna Flyer, February 2018
“Dissecting a Dry Air Pump” by Jacqueline Shipe 
Cessna Flyer, June 2017
“I Found This in my Oil” by Jacqueline Shipe 
Cessna Flyer, May 2017