Your Engine Probably Gave You Warning Signs. You Just Didn't Notice Them.
Most aircraft engine problems don’t appear out of nowhere.
In many cases, the warning signs are there weeks, months, or even years before the issue becomes serious. The problem is that most aircraft owners never see them.
Take exhaust valve failures as an example.
A failing exhaust valve will often produce characteristic oscillations in exhaust gas temperature. The pilot will not notice anything unusual in flight. The engine may appear to run perfectly normally. Yet a proper engine data analysis can identify the developing problem long before it becomes an operational issue. The suspected cylinder can then be inspected with a borescope, the diagnosis confirmed, and corrective action taken before a failure occurs.
Another example is a gradual change in fuel flow.
Because these changes usually develop slowly over time, many pilots simply adapt to the new normal. The corresponding changes in exhaust gas temperatures and cylinder head temperatures become part of everyday operation and eventually go unnoticed. Human beings are remarkably poor at recognising gradual change. We become accustomed to it. Engine data analysis does not.
This is one of the fundamental reasons why engine condition monitoring is so powerful.
It identifies trends that owners, pilots, and maintenance providers fail to see. It allows developing issues to be detected before they become expensive, disruptive, or dangerous.
Establishing a proper engine condition monitoring system is one of the single best things you can do if your goal is professional aircraft ownership.
We have an internal slogan at Quest Aeronautics that I firmly believe in: Aircraft ownership without engine intelligence is guesswork.
The implementation of engine condition monitoring is actually straightforward, yet it is still ignored by many aircraft owners and by large parts of the aviation ecosystem. That is unfortunate because it can literally make the difference between a minor repair and a major failure.
Engine condition monitoring allows you to assess the past, understand the present, and identify developing trends that may affect the future. There is really no compelling reason why it should not be part of every aircraft ownership system.
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Why Aircraft Ownership Is Different From Other Purchases
What I have learned over time is that aircraft ownership is not too dissimilar from industries where the customer experience is less streamlined and less regulated than, for example, the automotive world.
Owning and operating an aircraft is more like building a house than buying a supercar.
You, or someone you hire, must oversee the project and understand the different roles of the contractors involved. In general aviation, those contractors are flight schools, instructors, aircraft manufacturers, dealers, brokers, maintenance providers, CAMOs, and many other stakeholders. Together, they form what I refer to as the aviation ecosystem.
Like in the construction industry, the biggest risk is becoming a passive customer and simply letting things happen.
As many people know, that is often a recipe for frustration and disappointment.
General aviation is no exception.
Why Most Aircraft Owners Are Flying Blind When It Comes to Engine Health
Most pilot-owners are never taught how to monitor engine health properly.
Instead, they are often told that safety and airworthiness come down to following the manufacturer’s instructions and maintaining the aircraft in accordance with the applicable maintenance programme. While compliance is obviously important, it does not automatically mean that you understand the actual condition of your engine.
Many aircraft owners also believe that more maintenance automatically equals more safety, while on-condition maintenance is somehow risky or irresponsible. In reality, neither position takes into account the actual condition, operation, or maintenance history of the engine.
The accident statistics tell a different story. Many engine-related problems occur following maintenance events, while others result from operational practices, installation issues, or design characteristics. We cannot change the engine’s design, and in most cases we have little influence over installation decisions, but we can monitor and manage maintenance and operational factors. More importantly, we can collect evidence that helps us identify and address issues before they escalate.
Why Owners Feel Uncertain About Engine Health
It is no surprise that many aircraft owners feel uncertain about their engines.
For decades, pilots have been told that they will damage the engine if they move the throttle, mixture, and propeller controls in the wrong sequence. Many have learned outdated leaning techniques and inherited operational myths that are still repeated today.
At the same time, they are often told that running components on condition is dangerous, that overhauls are always safer than targeted repairs, and that major maintenance interventions are the default solution whenever uncertainty exists.
Yet very few aircraft owners have ever been introduced to engine condition monitoring.
Instead of using evidence-based data, many owners rely on simplified rules of thumb, hangar talk, and information that may have been outdated for decades.
During one of our outreach conversations a while ago, I spoke with an aircraft owner who held multiple academic degrees in a technical field, including a PhD. Obviously, a very intelligent individual. Yet he still approached aircraft ownership through the default path rather than approaching it like a professional operator.
He only had analogue engine instruments installed, with one exhaust gas temperature gauge and one cylinder head temperature gauge. He did not know the engine limits and did not use proper leaning techniques, but routinely added five litres of fuel to “protect” the valves because that was what he had been taught.
During the same conversation, he mentioned that he had previously lost another aircraft in the ocean following a catastrophic engine failure. The suspected cause was sticky valves or valve head separation.
Despite that experience, he still had no meaningful way of monitoring engine health and no systematic approach to understanding what was happening inside the engine.
This is more common than many people realise.
Without engine condition monitoring, owners are often forced to rely on assumptions, habits, and opinions. They cannot see developing trends, they cannot verify whether their operating practices are helping or harming the engine, and they often have no way of independently assessing recommendations from maintenance providers.
As a result, many owners are effectively flying blind when it comes to engine health.
Why Annual and Condition Inspections Are Not Engine Condition Monitoring
Annual inspections, airworthiness reviews, and condition inspections all serve an important purpose. They assess the aircraft’s airworthiness and help ensure that it remains safe to operate.
However, they are snapshots in time.
They tell you what the aircraft looked like on the day of the inspection. They do not reveal how the engine has been performing over the previous year, nor do they identify developing trends that may become significant in the future.
A good example is the differential compression test. This test remains a standard inspection item, but its results can be highly dependent on the inspection procedure, equipment, engine temperature, and the experience of the mechanic performing it.
A small amount of deposit on a valve seat can produce a poor result, even though the cylinder may still be perfectly serviceable. Unfortunately, many owners are unaware that both Continental and Lycoming have published procedures that allow a failed compression test to be verified before concluding that a cylinder requires major work.
In many cases, aircraft owners agree to expensive repairs or overhauls simply because they lack additional data that could provide context.
Engine condition monitoring provides that context.
Why Maintenance Shops Cannot Solve This Problem for You
Maintenance shops are optimised to maintain and repair aircraft. They are also businesses that must manage revenue, workload, and liability.
That is not a criticism. It is simply reality.
The responsibility for making aircraft ownership work ultimately belongs to the owner.
Many aircraft owners hope that the aviation ecosystem will take care of everything for them, but every stakeholder has different incentives. A maintenance provider’s responsibility is to maintain the aircraft. It is not necessarily their responsibility to build a comprehensive ownership system around your aircraft.
The result is that many owners hand over the aircraft, approve recommendations, pay invoices, and collect the aircraft without ever developing a deeper understanding of what happened or why.
If you want to operate your aircraft professionally, you need your own system.
Engine Condition Monitoring: Your Aircraft's Health Dashboard
Engine condition monitoring will not solve every ownership problem. What it does provide is information that allows you to make informed, evidence-based decisions.
In that sense, engine condition monitoring is your aircraft’s health dashboard.
In business, what gets measured gets managed. Successful organisations track revenue, profitability, cash flow, and other key indicators because they understand that decisions are only as good as the information behind them.
Yet many owners manage a €500,000 to €1.7 million aircraft with less information than they use to manage a small department within their company.
The Three Questions Every Pilot-Owner Should Be Able To Answer
A proper engine condition monitoring system helps answer three critical questions:
- How is the engine performing?
- What is happening inside the engine?
- What can we actually see?
To answer those questions properly, engine condition monitoring relies on three pillars.
Engine Data Analysis
Displaying, recording, and analysing engine data is one of the most powerful tools available to aircraft owners.
Engine data analysis can identify mistuned magnetos, fuel system issues, developing induction leaks, abnormal operating temperatures, and even early signs of exhaust valve problems. It can also help owners evaluate operational practices such as leaning techniques, temperature management, and compliance with engine operating limitations.
In many ways, engine data analysis is comparable to a modern health monitoring device. A health tracker continuously records information about your body and allows you to identify trends that would otherwise go unnoticed.
Engine monitors perform the same function for aircraft engines.
The key is not simply collecting data. The value comes from analysing it consistently and using it to identify trends over time.
Oil, Filter and Particle Analysis
Oil analysis, oil filter inspections, and, where necessary, particle analysis provide a different perspective on engine health.
While engine data tells you how the engine is behaving, oil analysis can reveal what is happening internally.
Regular oil analyses can identify abnormal wear patterns, corrosion, contamination, and even induction leaks. Filter inspections and subsequent particle analysis can help determine which components may be generating metal and whether further investigation is required.
Oil analysis is similar to blood work. A single sample provides useful information, but the real value comes from monitoring changes over time. Trends often reveal developing issues long before they become operational problems.
Borescope Inspections
Whenever a spark plug is removed, a borescope inspection should be considered.
Borescope inspections provide a direct view inside the combustion chamber and allow assessment of valves, cylinder walls, piston crowns, and other critical components.
Unlike engine data or oil analysis, a borescope allows you to see the condition directly.
It is one of the fastest and most effective methods available for assessing cylinder health and is particularly valuable when engine data or oil analysis has already indicated that further investigation may be required.
Why All Three Pillars Matter
One of the most common mistakes aircraft owners make is assuming that a single monitoring tool can provide all the answers.
It cannot.
Engine data analysis, oil analysis, and borescope inspections each answer different questions. Sometimes they identify the same issue at different stages. Sometimes one method identifies a problem that the others do not.
An exhaust valve problem may first appear in engine data. A borescope inspection may later confirm the diagnosis. Oil analysis may show no indication at all.
An induction leak may appear in engine data and eventually influence oil analysis results while remaining invisible during a borescope inspection.
The value comes from combining all three sources of information.
Unfortunately, many operators only perform oil analysis after an obvious failure has already occurred. At that point the report simply confirms what everyone already knows.
The interesting oil samples are often the ones collected months or years before the failure. Those are the samples that reveal trends and create opportunities for preventive action.
The same principle applies to engine data and borescope inspections.
Engine condition monitoring is not about identifying failures after they happen.
It is about identifying trends early enough that failures never occur in the first place.
How To Build a Practical Engine Condition Monitoring System
Implementing an engine condition monitoring system does not have to be complicated or expensive.
Depending on the aircraft, there may be some initial investment required, particularly if an engine monitor unit needs to be installed. However, the long-term benefits generally outweigh the cost many times over.
The first step is ensuring that the aircraft can display and record key engine parameters such as manifold absolute pressure, engine RPM, fuel flow, outside air temperature, and individual cylinder head and exhaust gas temperatures for each cylinder.
The second step is establishing an engine data analysis process. This requires selecting an appropriate analysis platform and regularly uploading engine data for review.
The third step is setting up routine oil analysis. This involves selecting a laboratory, ordering oil sample kits, and ensuring that a sample is collected at every oil change.
The fourth step is standardising borescope inspections. Every time a spark plug is removed, an opportunity exists to inspect the cylinder and document its condition.
Most importantly, all three activities should become part of a repeatable ownership system rather than occasional maintenance tasks.
The Goal Is Not To Become an Aircraft Engineer
At this point, some owners begin to worry that implementing engine condition monitoring means becoming an amateur engineer.
It does not.
You do not need to interpret every chart, understand every wear metal trend, or become an expert in borescope image analysis.
What you need is a system.
The purpose of engine condition monitoring is not to replace maintenance professionals. It is to provide better information so that better decisions can be made.
Some maintenance providers may be reluctant to adopt these practices or follow owner-driven monitoring procedures. If that happens, it is worth asking whether they are the right partner for your ownership journey.
A competent maintenance provider should be technically capable, communicative, and willing to work collaboratively.
Many owners are also hesitant to invest in engine monitoring equipment, particularly when operating older aircraft. While the hesitation is understandable, it is often short-sighted.
An engine monitor and a structured monitoring programme are investments. Preventing a major repair, identifying a developing problem early, or avoiding an unnecessary overhaul can easily justify the cost.
Beyond that, a properly installed engine monitor and years of recorded engine data often increase the aircraft’s attractiveness and value when it eventually comes time to sell.
The Real Value of Engine Condition Monitoring
Many people think engine condition monitoring is simply another maintenance tool.
I think that misses the bigger picture.
The real value of engine condition monitoring is that it helps you make better decisions throughout the entire ownership journey.
Without meaningful data, aircraft ownership often becomes an exercise in reacting to events. Decisions are made based on assumptions, habits, opinions, and sometimes fear. An unexpected maintenance finding leads to uncertainty. A recommendation from a maintenance provider is accepted because there is no independent way to evaluate it. A developing issue remains unnoticed until it eventually becomes expensive, disruptive, or potentially dangerous.
Engine condition monitoring changes that.
By combining engine data analysis, oil analysis, and borescope inspections, owners gain objective information about the actual condition of the engine. That information provides context for maintenance decisions, helps identify developing problems before they become major repairs, and allows operational practices to be evaluated based on evidence rather than folklore.
Most importantly, it enables aircraft owners to participate actively in the decision-making process instead of simply reacting to whatever happens next.
That does not mean distrusting maintenance providers or attempting to become an aircraft engineer. It means having enough information to ask better questions, understand the implications of different options, and make informed decisions based on the actual condition of the engine.
In that sense, engine condition monitoring is ultimately a decision-support system rather than a maintenance activity.
And if your goal is to become an informed aircraft owner and operate your aircraft like a professional, it is one of the most valuable systems you can implement.
Learn How To Implement Engine Condition Monitoring Properly
If you want to build a practical engine condition monitoring system around your aircraft, our workshops provide a structured introduction to engine data analysis, oil analysis, borescope inspections, reliability-centred maintenance, and professional aircraft ownership.
The objective is not to turn you into an aircraft engineer.
The objective is to help you become an informed aircraft owner who can make better maintenance, operational, financial, and safety decisions with confidence.
Because aircraft ownership without engine intelligence is guesswork.
Frequently Asked Questions
Engine condition monitoring is a system that uses engine data, oil analysis, and borescope inspections to assess engine health and detect trends early.
It helps identify developing problems before they become expensive repairs or in-flight failures.
No. Annual inspections are snapshots in time and do not reveal long-term engine trends.
- Engine data analysis
- Oil analysis
- Borescope inspections
In most cases, yes. It improves decision-making, helps detect issues early, and can reduce long-term ownership costs.
Want to approach aircraft ownership with more structure?
About Quest Aeronautics
Quest Aeronautics is a state-certified engineering office for aviation, dedicated to shaping the future of general aviation by providing innovative and cost-effective solutions to enhance aircraft performance and operations. With a focus on CS/FAR-23 and experimental/amateur-built (E/A-B) aircraft, Quest Aeronautics provides a range of services including flight testing, aircraft operations and maintenance consulting, high-quality aviation products, and tailored support for E/A-B projects. Collaborating with industry-leading partners, Quest Aeronautics is committed to delivering unparalleled support and expertise to individuals and organisations in the general aviation market.
About Author
Sebastian, the founder of Quest Aeronautics, is a driven and enthusiastic individual with a passion for aviation. Before delving into aviation, he gained valuable experience as a chemical process engineer and laboratory technician. Sebastian holds a Master of Science in Engineering and a commercial pilot licence, with several fixed-wing aircraft ratings under his belt. He has also completed an introduction course for fixed-wing performance and flying qualities flight testing at the National Test Pilot School in Mojave, CA and is compliance verification engineer for flight.