Aircraft Engine Deep Dive: What Every Pilot Needs to Know

Considering a career as an airline pilot or A&P mechanic? If so, then understanding how an aircraft engine works is a must. As a mechanic, knowing the ins and outs under the cowling can help you build confidence as you diagnose problems and make repairs, whereas pilots who know their mechanics may be better prepared to recognize small issues before they turn into bigger problems.

And while engines can vary greatly from one model of airplane to the next, there are some basics of an aircraft engine that are more-or-less universal and that anybody who is serious about aviation should know.

We sat down with an A&P mechanic for an in-depth look at how the engine, fuel system, and oil system all work together. Watch the full conversation in the video below, then keep reading for a deeper breakdown of everything covered.

What Are You Actually Looking At?

On a typical trainer (like a Cessna 172 or a Piper Archer), you’ll typically find a four-cylinder, horizontally opposed engine, with common examples including the Lycoming O-320, Lycoming O-360, and Continental equivalent.

What does this mean? When speaking of aircraft engines, “horizontally opposed” simply means that the cylinders of the engine themselves extend from opposite sides of the crankcase (rather than being arranged in a line or a “V”). The idea behind this design is that it allows for a more compact, space-saving engine with a low nose profile, which optimizes forward visibility for pilots while reducing vibration. Win-win.

Under the cowling, you’ll see several key engine components that include:

Cylinder – Combustion chamber where fuel and air are burned to generate power.
Crankshaft – Converts the pistons’ reciprocating motion into rotary motion of the crankshaft, which then turns the propeller.
Magnetos – Self-contained ignition systems.
Aircraft carburetor or fuel servo – A fuel-metering device that delivers the correct air/fuel mixture to the engine’s cylinders.
Oil sump – A receptacle that stores engine aircraft oil.
Alternator – Converts mechanical engine power into electrical power, which is then used to charge the battery and run onboard electrical systems.

Knowing these basic systems of an aircraft is essential for any aspiring pilot or aircraft mechanic, and you can dive deeper into each component in the FAA Pilot’s Handbook of Aeronautical Knowledge (PHAK).

The Four-Stroke Cycle: How Your Engine Makes Power

Now that you have a better idea of the key systems that drive an aircraft engine, it’s time to dive a little deeper into the ins and outs of how power is generated through what’s known as the four-stroke cycle.

This cycle can be broken up into the following stages:

Intake – The piston draws fuel and air into the cylinder.
Compression – The mixture of air and fuel is squeezed before being ignited by magnetos near the top of the stroke.
Power – Combustion forces from compression push the piston downward, thus turning the crankshaft.
Exhaust – Burned gases are pushed from the cylinder, and the cycle repeats.

As the foundation of all reciprocating engines in aviation, the four-stroke cycle plays a critical role in ensuring fuel efficiency, mechanical reliability, and proper power output. To give you a better sense of the scale and importance of this cycle, a four-cylinder engine running at a cruise setting of 2,400 RPM produces approximately 4,800 of these combustion events every minute.

The Ignition System: Why You Have Two Magnetos

On an aircraft, magnetos play an important role as self-contained ignition systems that can generate their own electrical power independently of the aircraft’s alternator and battery. Because of this, most training aircraft are equipped with dual magnetos and dual spark plugs for additional redundancy and more complete combustion.

When pilots perform a routine run-up, they must test the function of each magneto by moving the ignition switch back and forth, switching sequence to check for drops in RPMs. Although a small drop of about 125 RPM is considered normal (provided that the difference between magnetos is no more than 50 RPM), larger drops could indicate a failing spark plug or other ignition problems that should be investigated before flight.

Following the Fuel: From Tank to Cylinder

As much as an aircraft relies on the four-stroke cycle and ignition system to take flight, the aircraft fuel system is just as important. After all, you can’t run an engine without the proper flow of fuel from tank to cylinder.

Fuel systems can be complicated because different types of planes use different systems. High-wing trainers, for example, often use gravity-feed systems that allow fuel to flow naturally from tanks into their respective engines. Low-wing aircraft, on the other hand, are more likely to rely on engine-driven fuel pumps and/or auxiliary pumps to get fuel where it needs to go.

Regardless of fuel system, pilots have a responsibility to sump fuel ahead of every flight. This process involves draining samples from each tank, using a fuel strainer to check for signs of water contamination and to ensure that the proper type of fuel has been used.

Often, fuel type can be identified by color alone. Blue, for example, indicates the presence of 100LL Avgas, where jet fuel is typically clear or straw-colored. Confirming that the right fuel has been used is critical because the wrong type can quickly destroy an aircraft engine.

Carburetor vs. Fuel Injection: What Is the Real Difference?

Modern aircraft engines can be carbureted or fuel-injected, with the primary difference lying in how fuel and air are delivered. Specifically, a carburetor uses a venturi to mix fuel and air before distributing the mixture to all cylinders, while fuel-injected engines deliver fuel directly to each cylinder through a dedicated intake port.

There are potential pros and cons to each setup. A carburetor, for instance, offers simple and reliable delivery of fuel and air. However, these types of engines can also be susceptible to carburetor ice. Even on warm, humid days, a gradual drop in RPM could be indicative of this problem, so pilots need to be prepared to apply carburetor heat to melt ice if the issue arises.

Fuel-injected systems, on the other hand, provide a more precise delivery of fuel and air that can reduce the likelihood of ice problems. On the other hand, these engines may be more difficult to restart after a hot shutdown if fuel vaporizes inside the fuel lines. When this happens, pilots must be prepared to follow manufacturer-specific hot-start procedures for a safe restart.

The Oil System: Your Engine’s Lifeline

Beyond lubricating the many moving parts of an aircraft’s engine, an airplane’s oil system also plays a critical role in cooling internal components, carrying contaminants to the oil filter, and even providing hydraulic pressure to change blade pitch in planes with constant-speed propellers.

Many trainer aircraft feature a wet-sump system, where oil is stored in a sump below the engine and is circulated through the filter and cooler using a pump.

Before flight, it is essential to ensure that the quantity of oil meets minimum requirements specified in the Pilot’s Operating Handbook (POH). The oil should always be aviation-specific (follow manufacturer’s guidance), never automotive motor oil.

Upon starting the aircraft’s engine, pilots should also ensure that the oil pressure rises steadily within the first 30 seconds (otherwise, engines should be shut down and the issue investigated). Throughout flight, oil pressure and temperature should be continuously monitored, as discrepancies could indicate engine damage or other potential issues that require immediate action.

What Your Engine Instruments Are Telling You

Getting into the habit of performing consistent engine scans during flight can help pilots detect and address problems sooner rather than later. Here are some of the most important instruments to include in your scan and what each can tell you:

Tachometer – Provides a real-time RPM reading.
Oil pressure – Should remain steady in the green range, with a sudden drop requiring immediate attention.
Oil temperature – Normally rises gradually before stabilizing during cruise. Watch for rapid increases or decreases.
Fuel pressure – Indicates whether fuel is being delivered under proper pressure to the engine.
Exhaust gas temperature (EGT), if equipped – Displays temperature of the gases as they exit the engine.

Learn More in MzeroA’s Private Pilot Course

A solid understanding of how aircraft engine systems work is essential for passing your FAA knowledge exam, and even more so for flying safely.

In MzeroA’s Private Pilot Course, students explore a combination of systems instruction and real-world flight training to build confidence and practical skills. Reach out to learn more or get started today!

Know your airplane. It will take better care of you.