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Commercial pilot · ACS CA.IX.C · lesson pack

Systems and Equipment Malfunctions

Why this one matters

Systems failures rarely bring an airplane down by themselves; the pilot's reaction does. Startle, fixation and skipping the checklist turn a manageable failure into an undesired airplane state. A commercial pilot in a complex airplane has more systems and must know each one's failure and fix.

1 · Know these cold

  • •Every malfunction starts the same way: fly the airplane, identify the problem, then run the checklist.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
  • •Power loss or a rough engine: best glide or the right airspeed first; carb heat on (carbureted); fuel selector to a tank with fuel or BOTH; mixture rich; fuel pump on if equipped; magnetos checked, then BOTH; then the checklist. With carb ice it may run rougher briefly as the ice melts; don't turn the heat off.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
  • •Alternator failure: shed electrical load, land before the battery runs out. Vacuum failure: cover the failed attitude and heading indicators, use the backups.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • •Blocked static source: altimeter frozen, VSI at zero, airspeed low above the blockage altitude and high below it; use the alternate static. Blocked pitot: with the drain blocked too, the airspeed acts like an altimeter; with the drain open, it falls to zero.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • •Landing gear won't extend: check the circuit breaker and position, then the manual (emergency) extension per the POH.(Airplane Flying Handbook (FAA-H-8083-3C), Transition to Complex and High-Performance Airplanes)
  • •Electrical fire or smoke: master and alternator off, other electrical switches off except ignition, vents and cabin heat closed, extinguisher, land as soon as possible; ventilate only after the fire is out. Restore power one switch at a time only if the fire is out and you need it to keep flying, pausing after each.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
  • •An open door in flight is usually a noise problem, not a flying one: fly the airplane and land to close it.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)

2 · The lesson

Power loss
  • Common causes: fuel mismanagement (an empty tank selected, exhaustion), carburetor or induction icing, a magneto or ignition fault, an incorrect mixture, a turbocharger or fuel injection fault, roughness or overheating. Low or fluctuating oil pressure with rising oil temperature: land at the nearest suitable airport, since a complete failure may be close.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
  • A partial power loss can be more dangerous than a complete one, because it tempts you to press on. Treat it as an emergency and head for the nearest suitable airport.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
Electrical, vacuum, pitot-static and displays
  • Electrical: an ammeter discharge or low-voltage light means the alternator is off-line; reset per the POH, shed load, and land. Know which items are on which bus.(PHAK (FAA-H-8083-25C), Aircraft Systems (oxygen and pressurization))
  • Vacuum: a low suction reading means the attitude and heading indicators will fail slowly; cross-check, cover them, and use the electric backups or partial panel.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Pitot inlet and drain both blocked: the airspeed acts like an altimeter (rising in a climb, falling in a descent, no response to speed changes level). Inlet blocked, drain open: it falls to zero. Altimeter and VSI stay normal. Pitot heat treats pitot icing only.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Static blocked: altimeter frozen, VSI at zero, airspeed low above the blockage altitude and high below it. The fix is the alternate static source; in most unpressurized airplanes the cabin pressure is a little lower, so the altimeter reads a little high, the airspeed fast, and the VSI shows a brief climb before settling; use the POH correction table. With no alternate source, breaking the VSI glass is the last resort.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Electronic display failure: the other display usually shows reversionary mode; use the standby instruments and know how to select reversion.(PHAK (FAA-H-8083-25C), Flight Instruments)
  • Gear or flap failure: check breakers and indications, then the POH emergency procedures (manual gear extension; a no-flap landing needs more runway). Inoperative or runaway trim: hold pressure, disconnect or pull the breaker, land.(Airplane Flying Handbook (FAA-H-8083-3C), Transition to Complex and High-Performance Airplanes; Your airplane's POH/AFM)
Smoke, fire, other systems and doors
  • Electrical fire: master and alternator off, switches off except ignition, vents closed, extinguisher, then ventilate once it's out; restore only essential items, one at a time, only if needed to keep flying. Engine fire: fuel off and the POH procedure.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
  • Other systems, first action, then the POH: oxygen or pressurization failure, oxygen on and descend (below 10,000 feet cabin altitude for an oxygen failure); deice or anti-ice failure in icing, exit the icing; autopilot malfunction or runaway, disconnect and hand-fly; inoperative trim, hold the pressure and land.(Your airplane's POH/AFM)
  • An inadvertently opened door or window: fly the airplane, don't try to close it in flight unless the POH says, and land.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
The pilot's side
  • Use the checklist, by memory for the immediate items, then by reading it, so you don't miss a step under stress.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)
  • Startle is real: a sudden failure can freeze you for seconds. Pause, breathe, fly the airplane, then work the problem by the checklist.(Risk Management Handbook (FAA-H-8083-2A))
  • An undesired airplane state (unusual attitude, low speed) often follows a malfunction you fixated on: keep the scan going.(Airplane Flying Handbook (FAA-H-8083-3C), Emergency Procedures)

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 are the first three things you do with any malfunction?”

  2. Understand Explain why

    “Why is a partial power loss dangerous?”

  3. Apply Use it on a flight

    “Climbing through clouds, the airspeed rises as you climb and drops as you descend. What's happening?”

4 · Common mistakes

  • Fixating on the failure.

    The airplane drifts into an undesired state.

    Instead: Keep flying; scan.

  • Skipping the checklist.

    Steps get missed under stress.

    Instead: Memory items, then read the checklist.

  • Pressing on with a partial failure.

    It may get worse far from an airport.

    Instead: Land at the nearest suitable airport.

5 · Quick check

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

  1. 1. In most unpressurized airplanes, what does the alternate static source do to indications?

  2. 2. What does a blocked pitot (with the drain blocked) do?

  3. 3. What instruments does a vacuum failure affect?

  4. 4. What's the first action when a door pops open after takeoff?

  5. Scenario5. The engine runs rough at cruise in humid air with a carburetor. What do you suspect and do?

Trained it? Now prove it: practice systems and equipment malfunctions out loud with our examiner.

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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

Over forest, you smell burning insulation and see smoke from behind the panel.

How do the malfunction, the descent and the landing tie together? Decide, then see the worked answer

Treat it as an electrical fire and follow your airplane's POH, which governs; the general pattern is this. Isolate the affected circuit first if you can identify it. If you can't, master switch OFF, alternator or generator OFF, and all other electrical switches OFF except the ignition. Never reset a circuit breaker that tripped. While the fire is active, close the vents, cabin air and heat, and use the fire extinguisher if you have one; ventilate only after you've confirmed the fire is out. With the master off, the engine keeps running on its magnetos, but you lose the radios and transponder, and often electric flaps and gear. So declare the emergency before the master goes off if you can, plan on the emergency gear extension, and be ready for a no-flap approach. Fire in flight is time critical: start an emergency descent and land as soon as possible at the best suitable site you can reach. Pick it early and judge it: over forest, an open field, or a road only if it's clear of wires and traffic and long enough. After landing, the ELT and survival gear matter, so know where they are.

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

Brings together: Emergency Descent · 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; Commercial Pilot ACS (FAA-S-ACS-7B); Your airplane's POH/AFM. Checked against current sources 2026-11-13.