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Private pilot · ACS PA.IX.C · lesson pack

Systems and Equipment Malfunctions

Why this one matters

Malfunctions rarely kill on their own; the pilot’s reaction does. A popped door, an alternator light or an unreliable airspeed indicator have all led to accidents because the pilot stopped flying the airplane to fix it. Knowing what each failure looks like, and having a plan, keeps the airplane under control and on its way to a safe landing.

1 · Know these cold

  • •Fly the airplane first, then identify the problem, then use the checklist. Startle is normal: pause, breathe, fly.(Risk Management Handbook (FAA-H-8083-2A))
  • •Partial power loss or a rough engine: carburetor heat, fuel selector, mixture, magnetos per the POH, and plan to land soon.(Your airplane's POH/AFM)
  • •Alternator failure: the ammeter shows a discharge or a low-voltage light comes on. Check the alternator switch and breaker and reset once if the POH allows; if it won't restore, shed non-essential loads, tell ATC and land as soon as practical, planning on roughly 30 minutes of battery for essential equipment only.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • •Vacuum failure takes out the attitude and heading indicators in many airplanes: cross-check, cover them, and use the turn coordinator and standby instruments.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • •Blocked pitot (ram and drain): the airspeed indicator acts like an altimeter. Blocked static: the altimeter freezes and the VSI shows zero; use the alternate static source (it reads slightly high).(PHAK (FAA-H-8083-25C), Flight Instruments)
  • •Smoke or fire: follow the POH. For an electrical fire, typically master off, vents as directed, extinguisher if needed, then land.(Your airplane's POH/AFM)
  • •A door opening in flight is noisy but rarely dangerous: fly the airplane, and land to close it.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)

2 · The lesson

Engine, electrical and instruments
  • Rough running or partial power loss can be carburetor or induction icing, fuel starvation, a mixture problem or a magneto fault. Work it as a flow: scan the engine gauges, hold a safe airspeed and pick a landing field early (a partial loss can become a complete one), then carburetor heat if you have it and the POH checklist. With carburetor ice the engine runs briefly worse as the ice melts: leave the heat on long enough to work before ruling ice out. Land as soon as practical.(Your airplane's POH/AFM)
  • Low or zero oil pressure, especially with rising oil temperature, means the engine is about to fail: follow the POH, reduce power as directed, land as soon as possible and prepare for a forced landing. Don't keep going hoping it recovers.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Engine overheating (high cylinder head or oil temperature, from a long low-speed climb, a lean mixture, low oil or a cooling problem): enrich the mixture, reduce power and the climb angle to get more cooling air, per the POH, and land if the temperatures don't come back to the green.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Electrical: a low-voltage light or ammeter discharge means the battery is carrying the load. Shed non-essential loads, tell ATC, and land soon; plan for radios and lights to fail.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • Vacuum or pressure failure: the vacuum gauge drops and the gyro attitude and heading indicators slowly drift and fail. Cover them and use the turn coordinator, the compass and outside references.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Pitot blockages: ram inlet blocked with the drain open, the trapped pressure bleeds out and the airspeed falls to zero; ram and drain both blocked (static clear), it acts like an altimeter, higher in a climb, lower in a descent, and doesn't respond to speed changes in level flight; the drain alone blocked, no effect. Pitot heat helps if it’s ice.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Static port blocked: the altimeter freezes at the altitude where it blocked and the VSI shows zero; the airspeed reads low above that altitude and high below it, correct only at it. The alternate static source uses cabin air, at lower pressure than outside, so the altimeter reads high, the airspeed reads fast, and the VSI shows a momentary climb.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Glass cockpit failures: one display failing puts its information on the other in reversionary mode. An AHRS or air data computer failure flags or corrupts the attitude or air data: cross-check and fly the standby instruments, which may be only partial. Know where they are before you need them.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Flap problems: if the flaps stop or extend unevenly (one side), stop moving them, return them to the last symmetric setting if you can, and plan a no-flap landing. Split flaps roll the airplane hard toward the retracted side: counter promptly with aileron and rudder, keep the airspeed up, and fly the no-flap or partial-flap approach at the POH speed, expecting a faster approach and a longer landing roll. Inoperative trim means higher control forces: hold or re-trim with what works and land.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
  • Runaway trim is different: keep control against the trim force first, then stop it per the POH (hold the trim wheel, pull the trim breaker, disconnect the autopilot or electric trim), re-trim by hand if you can, and land, expecting very heavy forces.(Your airplane's POH/AFM)
  • Landing gear that won't extend (retractable): recycle and troubleshoot per the POH, use the emergency extension, confirm down-and-locked by every indication (a tower fly-by if available), and prepare for a gear-up or partial-gear landing if it won't come down.(Your airplane's POH/AFM)
Fire, smoke, systems and doors
  • Electrical fire: master off and all other electrical switches off, vents, cabin air and heat closed while it burns, extinguisher if available. Ventilate only once the fire is confirmed out, to clear the smoke, and restore electrics one item at a time only if essential, per the POH. Land as soon as possible.(Your airplane's POH/AFM)
  • Engine fire during start on the ground: keep cranking to draw the flames in, mixture idle cutoff, fuel selector off, throttle open per the POH; then master and magnetos off, extinguisher, get out, and have it inspected before any restart.(Your airplane's POH/AFM)
  • Engine fire in flight: throttle closed, fuel off, mixture idle cutoff, fuel pump off, cabin heat off, master off once you no longer need the radio; fly the POH airspeed or an emergency descent to find a mixture that won't burn; don't restart; and complete a power-off forced landing.(Your airplane's POH/AFM)
  • Other systems: if the oxygen fails, descend promptly to an altitude that doesn't need it (below about 10,000 feet) and watch for hypoxia. If anti-ice or deice fails in icing, leave the icing at once (change altitude or course, tell ATC, declare if needed), and expect higher stall speeds and longer landings.(PHAK (FAA-H-8083-25C), Aircraft Systems)
  • A door or window opening in flight is loud and startling, but most airplanes fly normally. Fly the airplane, don’t try to close it in flight unless the POH allows, and land.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
Startle, checklists and staying in control
  • Startle is the instant shock of something unexpected: it can freeze you or cause a sudden wrong input. Pause, keep flying, then assess.(Risk Management Handbook (FAA-H-8083-2A))
  • Use the checklist: memory items for the urgent steps, then the written list to confirm. Don’t let it take your attention off flying.(Risk Management Handbook (FAA-H-8083-2A))
  • An undesired aircraft state, such as unusual attitude, low speed or high descent rate, often follows a malfunction. Recover the airplane first, then the system.(Airplane Flying Handbook (FAA-H-8083-3C), Maintaining Aircraft Control: Upset Prevention and Recovery (stalls and spins))

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

    “What does a blocked static port do to the altimeter and VSI?”

  2. Understand Explain why

    “Why land soon after an alternator failure, even in good weather?”

  3. Apply Use it on a flight

    “The passenger door pops open just after takeoff. What do you do?”

4 · Common mistakes

  • Fixing before flying.

    Attention on the problem lets the airplane wander into a stall or descent.

    Instead: Aviate first; troubleshoot after the airplane is under control.

  • Trusting a failed instrument.

    A gyro failure or blocked pitot gives convincing wrong information.

    Instead: Cross-check instruments against each other and outside references.

  • Skipping the checklist.

    Under stress, steps get missed.

    Instead: Do memory items, then confirm with the written checklist.

5 · Quick check

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

  1. 1. What instruments fail with a vacuum failure in many light airplanes?

  2. 2. With the pitot tube and drain blocked, what does the airspeed indicator do in a climb?

  3. 3. What does the alternate static source do?

  4. 4. Alternator failure: what are your first actions?

  5. 5. What is the startle response, and how do you handle it?

  6. Scenario6. Your engine runs rough in moist, cool air with the throttle back. What’s a likely cause?

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Connect it

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

Connect it · Emergency Operations

At 4,500 feet AGL over rough country, oil pressure is dropping and oil temperature rising. The engine still runs.

How do the malfunction, the landing decision and your survival gear connect? Decide, then see the worked answer

Know the split. Low oil pressure alone, with normal temperature, can be a gauge problem: watch the temperature and land at the nearest airport to have it checked. Falling pressure with rising temperature means the engine may be losing its oil and could fail soon: land as soon as possible, while you still have power and height. Reduce power to the minimum you need to reach your chosen spot, to ease the load on the engine. Pick the nearest suitable airport or the best field within glide, and prepare for a power-off landing. Aviate and navigate first, then run the POH checklist and communicate: squawk 7700 and declare the emergency on the frequency you're using, with your position; use 121.5 only if you aren't talking to anyone. If the engine fails, fly best glide to the field you already picked. Know where the survival gear is and that the ELT is armed, because rough country means help can take time.

AFH (FAA-H-8083-3C), Emergency Procedures; PHAK (FAA-H-8083-25C), Aircraft Systems; AIM 6-3-1

Brings together: Emergency Approach and Landing (Simulated) · Systems and Equipment Malfunctions · Emergency Equipment and Survival Gear

Teaching this? The instructor lesson plan →

Study aid, not FAA guidance. Sources: Airplane Flying Handbook (FAA-H-8083-3C); Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C); Aeronautical Information Manual (AIM); 14 CFR Part 91; Private Pilot ACS (FAA-S-ACS-6C); Your airplane's POH/AFM. Checked against current sources 2026-11-12.