Private pilot · ACS PA.IX.C
Systems and Equipment Malfunctions
This task covers the failures you’re most likely to meet in a light airplane: engine roughness or power loss, electrical, vacuum, pitot-static, displays, flaps and trim, fire and smoke, and doors.
For each: what it looks like, why it matters, and the first things you do, always backed by your POH.
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.
Can’t miss
- •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)
What you should know
Engine, electrical and instruments K1 · K2
- 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 K3 · K4 · K5
- 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 R1 · R2 · R3 · R4
- 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))
Scenarios
Decide what you would do first, then see the worked answer.
Climbing out, the airspeed indicator keeps increasing as you climb, past numbers that make no sense for the attitude.
What’s likely, and what do you do? See the worked answer
A blocked pitot tube and drain: the indicator is acting like an altimeter. Use pitch and power settings you know, turn on pitot heat, and cross-check with GPS groundspeed.
PHAK (FAA-H-8083-25C), Flight Instruments
At night you notice the low-voltage light and dimming panel lights.
What do you do? See the worked answer
Check the alternator breaker and switch, shed non-essential loads, tell ATC you have an electrical problem, and land at the nearest suitable airport. Have a flashlight ready.
PHAK (FAA-H-8083-25C), Aircraft Systems
You smell burning insulation and see light smoke from behind the panel.
What do you do? See the worked answer
Fly the airplane, then run the POH electrical fire checklist, typically master off, then deal with the smoke and land as soon as possible.
Your airplane's POH/AFM
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.
Now train it
Say it out loud, hear it asked, and take the quick check in this lesson’s practice pack. It tracks your shaky spots.
Got it?
When it feels solid, practice systems and equipment malfunctions out loud with our examiner.
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Sources
- Airplane Flying Handbook (FAA-H-8083-3C): Emergency Procedures; Upset Prevention and Recovery
- Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C): Aerodynamics of Flight; Flight Instruments; Aircraft Systems
- Aeronautical Information Manual (AIM): Chapter 6, Emergency Procedures
- 14 CFR Part 91: 91.3, 91.205, 91.207
- Private Pilot ACS (FAA-S-ACS-6C): Areas VII and IX
- Your airplane's POH/AFM: Section 3, Emergency Procedures
Study aid, not FAA guidance. Regulations change; check the current text at eCFR and the ACS. Checked against current sources 2026-11-12.