Aircraft Systems

Start with the airplane you will fly

Two familiar-looking trainers can have different engines, propellers, fuel selectors, electrical systems, and instruments. Start with the airplane flight manual or pilot’s operating handbook (AFM/POH) applicable to the actual airplane, including its installed-equipment supplements and placards. A generic information manual is useful for study but cannot replace that aircraft’s operating documents.

Find the systems descriptions, limitations, normal procedures, and abnormal or emergency procedures. Be able to point to the fuel selector, electrical switches, engine controls, relevant gauges, and warning indications before departure. Knowing a component’s purpose helps explain a checklist item; it does not replace performing the item as specified.

This lesson describes common single-engine piston training airplanes. Diesel engines, electronic ignition, electric propulsion, and other installations can have different dependencies. No particular airplane’s settings, operating limits, or emergency switch sequence is supplied here.

PHAK Chapter 9, pp. 9-1–9-5: AFM/POH organization and supplements

The engine supplies power; the propeller produces thrust

A common four-stroke piston engine repeats intake, compression, power, and exhaust. A fuel-air charge enters a cylinder, the piston compresses it, ignition starts combustion, and the expanding gas drives the piston. The crankshaft converts the piston’s movement into rotation; exhaust gases then leave the cylinder. This sequence requires an adequate fuel-air supply, correctly timed ignition, and a serviceable engine.

The propeller’s rotating blades produce thrust. With a fixed-pitch propeller, blade angle cannot be changed in flight; RPM varies with throttle, airspeed, and load. A tachometer measures RPM, but the same RPM at different altitude or flight conditions does not necessarily mean the same engine power.

A constant-speed propeller uses a governor to vary blade angle and hold the selected RPM within its operating range. Throttle and propeller control have different jobs; manifold pressure and RPM are considered together when selecting power. The governor cannot maintain RPM beyond its available blade-angle range. Use the airplane’s approved combinations and limitations rather than a generic rule about lever order or gauge numbers.

PHAK Chapter 7, pp. 7-2–7-7: reciprocating engines and propellers

Trace fuel, air, and ignition separately

Trace fuel from the tanks, through the installed selector, strainers and pumps, to the engine. Some systems use gravity feed; others require pumps. Tank vents let pressure equalize as fuel is used. Selector positions, usable quantities, tank restrictions, and pump procedures belong to the actual aircraft. A position marked BOTH in one airplane does not establish that another airplane has that position or can use it for takeoff.

Verify fuel quantity by the airplane’s approved inspection method and compare it with the gauges and your fuel plan. Check fuel type and contamination using the checklist. Fuel on board and fuel reaching the engine are different questions: an incorrect selection, blocked vent, contamination, or pump problem can interrupt the supply.

A carburetor mixes fuel with incoming air before the mixture reaches the cylinders; a fuel-injection system meters fuel through its installed injection arrangement. Mixture control adjusts the fuel-air proportion. The correct adjustment method depends on the engine and operating condition.

Fuel vaporization and the pressure drop in a carburetor can cool it enough to form ice, even when outside air is above freezing. Restricted airflow can reduce power. A fixed-pitch installation may show falling RPM; a constant-speed installation may first show falling manifold pressure. Apply the applicable procedure rather than assuming all power loss is carburetor ice. Fuel injection avoids the float-carburetor icing mechanism, but intake obstruction or induction icing can still occur.

Many conventional spark-ignition aircraft engines use two independent magnetos. They generate ignition energy from engine rotation, independently of the main electrical bus. An alternator failure therefore does not automatically stop such an engine. That conclusion cannot be transferred to an installation with electrically dependent ignition or fuel equipment. Treat the propeller as capable of moving unexpectedly: switching off the master is not assurance that the ignition is safe, and a defective magneto grounding circuit can leave ignition live.

PHAK Chapter 7, pp. 7-7–7-11, 7-15–7-16, and 7-25–7-28: induction, ignition, and fuel

Oil and cooling protect the engine

Oil reduces friction, carries away heat and contaminants, and helps seal the piston-to-cylinder interface. Oil quantity, pressure, and temperature tell you different things. A correct quantity on the dipstick does not prove the engine has normal pressure after starting. Pressure indicates the condition of the circulating supply; temperature indicates how hot the oil is and generally changes more slowly.

Many small piston engines are air cooled. Cowling openings, baffles, and cylinder fins direct airflow through the engine compartment. Oil also contributes to cooling. High power with low airflow can make heat management more demanding. Some airplanes have cowl flaps, liquid cooling, or other arrangements; identify yours instead of assuming a control exists.

Monitor the applicable oil and cylinder-temperature indications against the published limits and expected trends. Unexpected low oil pressure, rising temperature, roughness, or loss of power requires prompt attention under the airplane’s procedure. One gauge does not prove the cause. During a ground check, resolve abnormal indications before takeoff; aloft, maintain control and use the appropriate checklist and landing decision.

PHAK Chapter 7, pp. 7-16–7-18: oil and engine cooling

Electrical power has a source, a path, and a load

The battery stores electrical energy. An engine-driven alternator or generator normally supplies the operating electrical system and replenishes the battery. A bus distributes power to connected equipment through protected circuits. Radios, displays, lights, pumps, and other equipment consume that power according to the installation.

If charging fails, equipment can continue operating on the battery until the remaining supply is insufficient. A working radio or illuminated display therefore does not prove the charging system is healthy. Warning lights, voltage, and an ammeter or loadmeter help identify the situation; learn what the installed meter actually measures. No battery endurance is assumed in this lesson.

Circuit protection opening is evidence of a problem, not an instruction to repeatedly reset it. Follow the aircraft procedure. Any smoke, burning smell, or heat changes the urgency and calls for the applicable emergency response. Electrical faults can remove capabilities needed for the planned route even while the engine continues running.

PHAK Chapter 7, pp. 7-15–7-16 and 7-30–7-33: magnetos and electrical systems

Controls, landing gear, and brakes vary by installation

On many trainers, cables or pushrods connect the pilot’s controls to the primary control surfaces. Other designs use powered or electronic controls. Flaps and trim may be manual or electric. The Control Surfaces lesson explains the aerodynamic job of each surface; here, identify how the installed system moves it and how its operation is checked.

Fixed landing gear remains extended. Retractable gear adds an extension system, indications, limitations, and an aircraft-specific abnormal-extension procedure. Nosewheel and tailwheel arrangements also have different ground-handling characteristics. Recognize the arrangement you will operate and obtain instruction for it.

Main-wheel brakes slow the airplane on the ground. Differential braking can assist steering, and many small-airplane brakes use hydraulic pressure. The hydraulic arrangement, pedals, parking brake, and steering connections vary. A fluid leak, abnormal brake response, unexpected control resistance, or an unsatisfactory gear indication needs investigation. Knowing how another trainer behaves is insufficient evidence that this airplane is ready.

PHAK Chapter 6, pp. 6-1–6-3 and 6-8–6-11: control arrangements, flaps, and trim · PHAK Chapter 7, pp. 7-31–7-34: hydraulics, landing gear, and brakes

Use checks to establish that the system works

A useful check has an expected result. Before the flight, find the permitted engine indications, ignition-check criteria, electrical indications, and control checks in the applicable checklist and manual. Then compare the observed result with that requirement. An unresolved result is not acceptable merely because the engine sounds normal or the last pilot completed a flight.

When something changes aloft, keep aircraft control and safe flight conditions first. Identify the indication, cross-check related evidence, and use the applicable abnormal or emergency procedure. Consider what else depends on the affected system and whether the planned flight remains practical. Use ATC, another qualified pilot, and a suitable landing option as available; avoid spending the remaining margin on open-ended troubleshooting.

For your own training airplane, explain three links to your instructor: how fuel reaches the engine, what continues after a charging-system failure, and what evidence would stop the before-takeoff check. These explanations prepare you to use that airplane’s checklist; they are not a substitute for its procedures or flight instruction.

PHAK Chapter 9, pp. 9-2–9-5: limitations, normal/emergency procedures, and supplements

FLIGHT SCENARIO

What would change your plan?

Continue studying

Connect this lesson with related concepts:

• Read the airplane’s instruments
• Evaluate an inoperative item before departure