Will the Engine Continue to Run When the Master Switch is Turned Off in Airplane

Aircraft engines are extremely reliable when properly cared for, and can deliver years of safe flight. That being said, not all pilots know as much as they should about the proper care and maintenance of engines, or that mechanical failure accounts for 15 to 20 percent of all accidents. Knowing how to manage a power plant helps you fly more safely and can minimize the cost of flying. Whether the aircraft you fly is equipped with a sophisticated engine monitoring system or not, a basic understanding of how engines work is required to correctly diagnose potential engine problems. For all engines air is drawn into the engine, mixes with fuel, burns at a controlled rate and expands, pushing on a piston that turns the crankshaft and propeller. Most piston aircraft engines develop power with four cycles, or strokes, of each piston inside a cylinder. The four cycles are intake, compression, power, and exhaust. Cockpit engine controls, usually the throttle, prop control and mixture, allow a pilot to extract the most efficient performance from the engine and ensure safe and reliable operation.

Throttle = Air and Fuel

The throttle is an air valve, opened all the way for full power and closed almost completely at idle. In a carbureted engine, as the throttle is opened further and further, more and more fuel is automatically drawn through the carburetor. The fuel and air combine in the carburetor throat and are sucked into the cylinder via intake tubes. In a fuel-injected engine, the pilot still controls the volume of air entering the engine by moving the throttle, but the
fuel is delivered separately into each cylinder, mixing with the air inside the cylinders. Fuel-injected engines are more efficient and develop more power than the same-size carbureted
engine because of more precise fuel delivery. With fuel-injected engines, there is no worry about carb ice, because there is no carburetor in which the fuel-air mixture can vaporize and cool. The main operational difference with fuel-injected engines is that they can be harder to start, especially when hot.

Magnetos = Spark

Aircraft engines have two spark plugs in each cylinder, to improve combustion efficiency and to provide a backup in case one ignition system fails. Feeding the spark plugs are two magnetos, each of which is self-contained and creates the spark, all without an external electrical source. In your car, if the electrical charging system fails or the ignition is turned off, your engine stops running. In an airplane, the electrical system can be turned off
with the master switch and the magneto-equipped engine will continue running.
Each magneto is independent, firing its own set of spark plugs. If one magneto fails, the aircraft will still fly safely on the other magneto and its set of spark plugs.

Getting Started

Most piston engines will start with the mixture rich, throttle advanced slightly, and fuel pump On. Still, starting an airplane engine isn't automatic, as it is in a car.

Carbureted Engine
On carbureted engines, cold starts are arguably the most difficult and provide a test of the pilot's understanding of aircraft systems.
To start a cold engine, add extra fuel by priming. This puts fuel directly into one or more cylinders (via the intake manifold). Refer to the aircraft's POH (pilots operating handbook) for the correct priming technique. Do not pump the throttle, as this will simply force raw
fuel (which doesn't vaporize as easily in cold weather) into the intake system, possibly causing an engine fire.

If the outside temperature is below 20 degrees F, the engine may need a preheat, both to aid in starting and prevent engine damage. During a cold start try to avoid draining the battery unnecessarily. Leave avionics, electric flaps, and aircraft lighting, which all rely on and use battery power, off until the engine is running.

NOTE: Excess priming causes large amounts of fuel to pool in the carburetor intake. This fuel can ignite if the engine backfires. Most POHs recommend that you keep trying to start the engine after the fire is noticed. This puts the fire out by pulling the flames back into the engine. If you get the engine started let it run for a few minutes before shutting down and examining the damage. If the engine does not start turn off the master and ignition switches as well as the fuel selector and mixture, abandon the aircraft, and look for a fire extinguisher or call the fire department.

Fuel-Injected Engine
For some fuel-injected engines that are already hot, engage the starter and allow the engine to turn while keeping the mixture at idle cutoff. When the engine catches, advance the mixture. If the engine is over-primed because the mixture was advanced too soon, it
may be flooded. The starting procedure for a flooded engine is similar to the hot-engine start, but the throttle may need to be opened (advanced or pushed in) in order to add air that will help purge the excess fuel.

Fuel-injected engines use electric primers or the electric fuel pump to spray fuel into the cylinders for priming. In some airplanes, the amount of primer fuel is adjusted by advancing the mixture and the throttle. It's easy to flood the engine, and then the flooded-start
procedure will be needed. A typical flooded (or hot-start procedure) for a fuel-injected
engine begins with the mixture at idle cutoff. Next, move the throttle to the open position (full power). Check the POH to see if the fuel pump needs to be On or Off.
While cranking the engine, get ready to reverse the throttle and mixture controls as the engine starts (quickly retard the throttle and slowly richen the mixture). It takes some
practice to gracefully hot-start a fuel-injected engine.

How to Make Your Engine Live Longer

First and foremost – try to fly your engine at least an hour a week. Far more engines rust out than wear out. They rust because the oil drains off the cylinder walls and the moisture in the air then reacts with the iron in the engine. The rust creates roughness, which increases wear. Piston aircraft engines are made mostly of steel and aluminum, which expand and contract at different rates, depending on temperature. When flying at varying altitudes and from one climatic zone to another, temperature changes can be extreme. By keeping large engine temperature changes over a short period of time to a minimum, and within prescribed limits, the safety, reliability and longevity of the engine are significantly enhanced. For example, avoiding rapid descents at idle power near your destination airport will help avoid "shock cooling," which is the too-rapid cooling of hot engine metals. Shock cooling causes stress that can lead to cylinder head cracks. To avoid this, begin descent planning farther out and descend at a slower rate with a low-cruise power setting. Good descent planning takes a little work, but your engine and passengers will thank you. This may take some negotiation with ATC, if IFR, or you may have to increase drag such as lowering the landing gear or flaps to keep airspeed and resultant engine cooling in check. Pilots have two ways to control engine temperatures: fuel flow (throttle and mixture) and airflow (pitch attitude and cowl flaps, if your airplane is so equipped). Fuel flow is a double-edged sword. As more fuel is provided to the engine (provided the mixture is set correctly), the more power is developed, which naturally means more heat. But extra fuel is also used as a cooling agent, which is one reason why mixtures are usually set full rich for takeoff and initial climb.

Cooling airflow and fuel-air mixture affect engine temperature, as well. The pilot's job is to keep engine temperatures at settings that maximize engine life. For example, an engine with a red line oil temperature of 250 degrees F will last much longer running at 180 degrees than 240 degrees. Keeping an engine too cool in flight can also be harmful; if oil cannot get hot
enough to burn off water that has condensed in it, internal engine rust can occur. Engine experts suggest an oil temperature of around 180 degrees or a little higher as a happy medium for typical air-cooled GA engines. Oil's primary function is to lubricate engine parts, but with the help of air flowing through the cowling and the oil cooler it also transfers heat out of the engine. There are two options for controlling oil cooling: Increase airflow through the engine and oil cooler by lowering the aircraft's pitch attitude or reducing power, if possible. If the airplane has cowl flaps, which increase the amount of air flowing over the engine, leave them open even after leveling off until temperatures stabilize – then close them as appropriate. On a hot day, climb at higher airspeeds and lower pitch attitudes
to keep engine temperatures in the green arc.

Common Engine Problems (and solutions)

What do I do if the engine runs rough during run-up?
Engine roughness while checking the magnetos during run-up could indicate a fouled spark plug or other ignition system problem. Accelerate the engine to run-up rpm and lean the mixture until the engine runs rough. Let the engine run for about 30 seconds. Enrich the mixture then check the mags again. If this doesn't clear the roughness, have the ignition system checked by a mechanic before flying. What if the mag drop is more than 200 rpm?
A larger than normal mag drop is not as critical as a rough mag. A smooth drop up to 200 rpm is fine. A drop greater than 200 rpm could indicate a mag-timing problem that
should be checked. A mis-timed magneto can rob some power from the engine and also cause engine damage.

Can I fly if the carb heat drop is 300 rpm or more during runup?
No. A large carb heat drop during runup, more than the typical 50 to 100 rpm, is caused by an exhaust leak inside the shroud where hot air is diverted to the carburetor. All exhaust leaks are dangerous and must be fixed, because firewall air leaks can allow exhaust fumes and possibly carbon monoxide from the engine compartment into the cockpit. A leak can also direct hot exhaust onto vulnerable components such as fuel lines and possibly cause a
fire in the engine compartment.

Is it possible for the carburetor to ice up during ground operations?
Yes. Under certain conditions carb icing can occur while taxiing. If you don't leave the carb heat on for at least 10 seconds during the runup check, the ice might not melt and could cause lower power output during takeoff and possibly engine failure. If the carburetor is iced up during runup, carb heat application will result in an initial small rpm drop, then a rise higher than the runup rpm.

How do I know if the engine is developing full power during takeoff?
The engine must reach the specified static rpm range (before releasing the brakes) at full rpm. Check the POH for these numbers. If the aircraft can't reach this rpm range on the ground there may be a problem with the tachometer indication or something wrong with the
engine. Possible problems include a worn propeller (fixed-pitch), improperly set propeller governor (constant- speed), mis-timed magnetos, fouled spark plugs, clogged fuel injector nozzle, or a blocked muffler.

What is a hot magneto and how can I troubleshoot this?
A "hot" magneto is a magneto that can't be turned off. If someone manually turns the prop with a hot mag, it could begin turning even though the magneto switch is in the Off position. There are two times you can easily check for a hot mag: during runup and at engine shutdown. If an rpm drop is not noticed during the mag check on runup, you may have a hot mag. During engine shutdown, check for a hot mag by running the engine at idle and turning
the ignition to Off. If the engine continues running with the ignition in the Off position, the mag is hot.

Why is my engine so hard to start, especially when hot, and what can I do about it?
There are many causes of hard starting, including a weak battery, fouled spark plugs, worn magnetos, worn impulse couplings, fuel vapor lock, and improper technique. Fuel-injected engines can be difficult to startwhen the engine is hot because fuel can turn into vapor in fuel lines near the hot engine. With air bubbles/vapor in the fuel lines the engine will not start or will not run after starting. One hot-start technique includes a method of purging the fuel lines to eliminate fuel vapor. Follow POH instructions for hot starting, but be sure that the mechanical items mentioned above aren't making the problem worse. If all else fails, ask your mechanic for his favorite hot starat technique.

My engine runs very rough while it's starting then smooths out as it warms up. Is there something wrong?
Yes, there is a strong likelihood that you have a stuck valve. The valve sticks inside the cylinder head when the engine is cold and the metal parts are contracted. As the engine warms up, the valve eventually loosens and the engine runs smoother. A stuck valve is dangerous because the sticking can occur during normal operations and it can cause catastrophic engine failure. Have this symptom checked thoroughly before flying.

Can I hurt my engine by leaning too much?
Yes, at higher power settings you can hurt the engine by over leaning. Follow the POH leaning instructions to avoid damage. There is one time that over leaning isn't a problem and that is when running at just above idle power during ground operations. During a long taxi or a lengthy wait for takeoff clearance, you can lean the engine aggressively without the risk of damage. Leaning on the ground helps prevent spark plug fouling. Just don't forget to enrich the mixture before takeoff.

Is it okay to lean below 3,000 feet?
Yes, you can lean the engine at any altitude. There is no reason not to lean during cruise; it saves gas and is better for the engine. While you will still see recommendations not to lean until reaching 3,000 or 5,000 feet, this advice is to keep pilots from forgetting to enrich the mixture before descending, and it is not related to any potential engine problems.

I learned what to do if the engine fails, but what do I do if there is just a partial power loss?
This is an important question. Instructors rarely teach partial power loss, but it is more likely to occur than a complete engine failure. Circumstances that can cause a partial
power loss vary, but the key is to determine if there is enough power to remain aloft to troubleshoot the problem. If the engine is losing power steadily, you'll need to find a
place to land quickly. An example might be a gradual loss of oil pressure; the end result is still total engine failure. A forced landing is in the very near future. A fuel line or muffler
blockage could cause a partial power failure but leave enough power to stay level. In this case, you may be able to nurse the airplane to a nearby airport, but this will depend on terrain and weather. The bottom line for partial power is to treat it like a full engine failure. Troubleshoot as needed but plan to land at the nearest suitable airport.

via AOPA SA25-10/05

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Source: https://sideslip.co.za/the-engine-is-the-beating-heart-of-the-airplane/

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