← Train

Private pilot · ACS PA.I.G · lesson pack

Operation of Systems

Why this one matters

System failures rarely cause accidents by themselves; the pilot's response does. Knowing how each system works lets you spot a failure early from the instruments, understand what it means, and handle it calmly with the checklist instead of being surprised.

1 · Know these cold

  • •The magnetos make ignition independently of the airplane's electrical system; the engine keeps running if the alternator or battery fails.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • •Carburetor ice can form in a wide range of temperatures with visible moisture or high humidity. Sign in a fixed-pitch airplane: dropping RPM. Fix: full carburetor heat.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • •Pitot-static: the airspeed indicator uses pitot and static; the altimeter and VSI use static only.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • •Vacuum failure: the attitude and heading indicators slowly become unreliable. Cross-check, cover them, and fly by the other instruments.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • •Alternator failure: the battery is all you have. Reduce electrical load and land as soon as practical.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • •Above 12,500 feet MSL for more than 30 minutes, and at all times above 14,000, the crew must use oxygen.(14 CFR 91.211)
  • •For any abnormality: fly the airplane, then the checklist, then decide and communicate.(PHAK (FAA-H-8083-25C), Aircraft Systems)

2 · The lesson

Flight controls
  • Primary controls: ailerons (roll), elevator (pitch), rudder (yaw).(PHAK (FAA-H-8083-25C), Flight Controls)
  • Secondary controls: flaps (more lift and drag, lower stall speed), trim (relieves control pressure) and, on some airplanes, spoilers.(PHAK (FAA-H-8083-25C), Flight Controls)
Engine, propeller, fuel and oil
  • Most training airplanes have a four-stroke (intake, compression, power, exhaust), horizontally opposed, air-cooled piston engine.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Dual magnetos give two independent ignition systems; the run-up checks each one.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Lean only as the POH directs: normally in cruise at 75% power or less, or at high density altitude. Don't lean aggressively for takeoff or a full-power climb, enrich before adding power or descending, and watch cylinder and oil temperatures.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Carburetor ice forms from fuel vaporization and the venturi effect, even well above freezing with humid air. It is most likely below about 70°F (21°C) with relative humidity above 80%, and can form at much warmer temperatures because the carburetor air can be up to about 70°F colder than outside. The risk is highest at low power: apply full carb heat before reducing power for a descent. Expect a further drop as the ice melts, and leave it on until RPM (fixed pitch) or manifold pressure (constant speed) recovers.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Fuel-injected engines can't get carburetor ice, but they can get induction (impact) icing that blocks the air intake or filter. Use the alternate air source per the POH.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Fixed-pitch propellers are set for one compromise. With a constant-speed propeller, the throttle sets manifold pressure (power, on the MP gauge) and the propeller control sets RPM, which the governor holds. Reducing power: manifold pressure first, then RPM. Increasing power: RPM first, then manifold pressure. Avoid high MP with low RPM beyond the POH limits.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • High-wing airplanes often feed fuel by gravity; low-wing airplanes need fuel pumps. Sump the tanks before flight to check for water and contamination; 100LL avgas is blue.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Detonation is explosive, uncontrolled burning of the mixture after normal spark ignition, from excess heat and pressure, low-grade fuel or overheating: reduce power, enrich the mixture and increase cooling. Preignition is ignition before the spark, from a hot spot such as a glowing deposit or damaged plug; it can cause detonation, roughness and severe damage.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Oil lubricates, cools, seals and cleans. Read the pressure and temperature together: low pressure with rising or high temperature means oil loss and coming engine failure, so land as soon as possible; low pressure with normal temperature is more likely a gauge or sensor fault, so monitor, follow the POH and land as soon as practical.(PHAK (FAA-H-8083-25C), Aircraft Systems)
Electrical, landing gear and the cabin
  • The alternator (or generator) powers the system and charges the battery; the master switch connects them. A center-zero ammeter shows the battery charging (+) or discharging (-): a discharge in flight means the alternator isn't carrying the load. A loadmeter shows the alternator's output: zero in flight means it has failed.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Hydraulics: pressurized fluid from a reservoir operates the wheel brakes in most trainers, and gear or flaps in some. Check brake feel and fluid per the POH; losing pressure means weak or no brakes (and gear or flap problems where fitted, with the emergency gear extension).(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Landing gear may be fixed or retractable; know your gear and brake systems and their checks.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Cabin heat usually comes from a shroud around the exhaust. An exhaust leak can put carbon monoxide in the cabin: carry a CO detector.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Anti-ice prevents ice from forming (pitot heat, carburetor heat, heated windshields and propellers, fluid systems); deice removes it after it forms (pneumatic boots, weeping-wing fluid). A typical trainer has only pitot heat, carb heat and defrost and is not approved for known icing: avoid icing, and leave it at once if you meet it.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Supplemental oxygen: crew above 12,500 to 14,000 feet MSL for more than 30 minutes, crew at all times above 14,000, and every occupant must be provided oxygen above 15,000.(14 CFR 91.211)
Flight instruments
  • Pitot-static instruments: airspeed indicator (pitot and static pressure), altimeter and vertical speed indicator (static only).(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Gyroscopic instruments: the attitude and heading indicators are usually vacuum-driven; the turn coordinator is usually electric, so one failure doesn't take all of them.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Glass cockpits replace these with an AHRS and an air data computer, with backup instruments. Know your backups.(PHAK (FAA-H-8083-25C), Flight Instruments)
Recognizing and handling failures
  • Blocked pitot tube, drain hole open: the airspeed drops to zero, while the altimeter and VSI work normally. Pitot inlet and drain both blocked (static open): the airspeed indicator acts like an altimeter, rising in a climb, falling in a descent and not responding to speed changes in level flight.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Blocked static port: the altimeter freezes, the VSI reads zero, and the airspeed reads low when you are above the altitude where it blocked and high below it. Open the alternate static source: the altimeter and airspeed usually read slightly high, the VSI shows a momentary climb before settling, and the POH may give a correction table.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Vacuum failure: the suction gauge drops and the attitude and heading indicators drift. Cross-check against the turn coordinator, airspeed and altimeter.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Alternator failure: the ammeter shows a discharge or the low-voltage light comes on. Turn off non-essential electrical equipment and land as soon as practical.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Rough engine: work the POH checklist in order (carburetor heat, throttle, mixture, fuel pump where fitted, fuel selector to the tank with the most fuel, primer locked) and pick a landing site. For the magnetos, try left, then right, then back to both; never select off in flight. If it runs smoothly on one magneto, stay on that one and land.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Scan the engine and system gauges regularly; early detection gives you time.(PHAK (FAA-H-8083-25C), Aircraft Systems)
Automation
  • Autopilots and GPS reduce workload but can fail or be set wrong. Know what mode it's in and what it will do next, and be ready to hand-fly.(PHAK (FAA-H-8083-25C), Flight Instruments; Advanced Avionics Handbook)
  • If the automation surprises you, disconnect it and fly.(Risk Management Handbook (FAA-H-8083-2A))
Avionics in your airplane
  • Know the installed avionics in the airplane you fly: communication and navigation radios, GPS, transponder and ADS-B, the audio panel and intercom, the autopilot, and on a glass panel the AHRS, air data computer and backup instruments. For each, know what it does, what powers it, and what you lose when it fails, from the POH and the avionics manuals.(PHAK (FAA-H-8083-25C), Flight Instruments; Advanced Avionics Handbook (FAA-H-8083-6))

Want it all on one page, with scenarios? Read the full lesson.

3 · Say it out loud

Answer each one out loud, then check yourself and mark how it went.

  1. Remember Recall it

    “Which instruments use the static system?”

  2. Understand Explain why

    “Why does the engine keep running if the alternator fails?”

  3. Apply Use it on a flight

    “In cruise, the RPM slowly drops in your fixed-pitch airplane on a humid day. What do you do?”

4 · Common mistakes

  • Saying the engine stops if the electrical system fails.

    Magnetos are self-contained.

    Instead: Know which systems depend on electrical power and which don't.

  • Removing carb heat when the RPM first drops further.

    The drop means ice is melting through the engine.

    Instead: Leave full carb heat on until the RPM recovers and stays steady.

  • Trusting a failed attitude indicator.

    A vacuum failure fails slowly and silently.

    Instead: Cross-check the instruments and check the suction gauge in your scan.

5 · Quick check

Answer, then reveal. Flag anything you want to see again.

  1. 1. What are the four strokes of a piston engine?

  2. 2. Which instruments does a vacuum failure affect in a typical training airplane?

  3. 3. Using the alternate static source, how do the altimeter and airspeed usually read?

  4. 4. When must the crew use supplemental oxygen?

  5. Scenario5. Your oil pressure is dropping and oil temperature rising in cruise. What do you do?

Trained it? Now prove it: practice operation of systems out loud with our examiner.

Start a practice oral on this task

Your progress is saved in this browser. Create a free account to keep it on every device, with your shaky spots and mock oral results in one place.

Connect it

One situation that runs across this lesson and its neighbors in the same ACS area. Decide first, then check.

Connect it · Preflight Preparation

A July afternoon. You plan a 90 NM trip from a 2,800-foot runway at 1,500 feet elevation; it's 33 °C. The destination TAF has a TEMPO for thunderstorms starting about when you'd arrive.

How do the weather, the airplane's performance and your fuel plan change one another, and what do you decide? Decide, then see the worked answer

Work the density altitude first. Standard temperature at 1,500 feet is about 12 °C, so 33 °C is about ISA +21 °C and the density altitude is roughly 4,000 feet (more if the pressure is low). Enter the POH takeoff and climb charts at the actual pressure altitude and temperature, never the field elevation, and compare the ground roll, the distance over a 50-foot obstacle and the climb with the 2,800 feet and the obstacles, with a margin. If it's tight, cut payload and baggage first. Never cut fuel below trip fuel plus fuel to divert to an alternate plus the 91.151(a)(1) day VFR reserve of 30 minutes at normal cruise. After any load change, recompute the weight and balance and the CG, and check the landing distance at the destination too. The TEMPO puts thunderstorms over the destination at your arrival. Don't plan to beat the TEMPO window or to divert closely around cells: avoid thunderstorms with severe or intense radar echoes by at least 20 miles, never take off or land in the face of an approaching thunderstorm, and wait storms out on the ground. With thin performance margins and storms at the far end, the better answer is the cooler, calmer morning.

PHAK (FAA-H-8083-25C), Aircraft Performance and Weather Theory; AC 00-24C, Thunderstorms; 14 CFR 91.103, 91.151

Brings together: Weather Information · Cross-Country Flight Planning · Performance and Limitations

Teaching this? The instructor lesson plan →

Study aid, not FAA guidance. Sources: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); Advanced Avionics Handbook (FAA-H-8083-6); 14 CFR 91.211; Your airplane's POH/AFM. Checked against current sources 2026-11-12.