Engine, electrical, pitot-static

A malfunction you understand is one you can fix; a malfunction you've only memorized is one that owns you. The point of this element isn't a list of failures — it's knowing the systems well enough that an abnormal indication tells you a story instead of just scaring you.

Engine: partial versus total power loss

Most engine trouble is a fuel, air, or ignition problem, and the cockpit responses target exactly those three. The instant the engine runs rough or quits, the first move is always the same: pitch for best glide (68 KIAS in the C172S at maximum gross weight) so the airplane is buying you time while your hands work the problem.

Then run the cause down in order:

• Fuel — fuel selector to BOTH, mixture rich, fuel quantity and the tank you're actually drawing from. The single most common "engine failure" in training airplanes is fuel mismanagement — a selector on a dry tank, not a broken engine.
• Air / induction — carburetor heat ON. In a carbureted C172, carburetor icing is the classic partial-power culprit, and it loves exactly the cool, moist, low-power conditions of a descent. The heat melts the ice; expect a brief further roughness as the melt-water passes, then smoothing.
• Ignition — magneto check (try L and R), primer in and locked. A rough mag or an unlocked primer leaning the mixture both show up here.

Partial power loss is the more insidious of the two: the engine is still making some thrust, which tempts a pilot to nurse it toward a far airport instead of landing while options are good. Treat a degrading engine as a landing decision (R2), not a "see if it clears up" decision.

Electrical: the battery becomes your clock

An alternator failure is the common electrical malfunction — you'll see the ammeter showing discharge or a low-voltage light. The key fact, and the one DPEs probe: the engine keeps running. Spark in a piston engine comes from engine-driven magnetos, which are completely independent of the ship's electrical system. So an electrical failure is an urgency, not an immediate emergency — you have a flying airplane, just a draining battery.

That battery is now a countdown. Shed nonessential electrical load — landing/taxi lights, extra avionics, pitot heat if not needed — to stretch the radios and transponder you'll want for the approach and for talking to ATC. Plan to land before the battery is exhausted rather than discovering it's dead on short final.

Pitot-static: when the instruments lie

The pitot-static instruments (airspeed, altimeter, VSI) read pressure, so a blockage makes them tell a confident lie. Knowing the signature tells you which instrument to stop trusting (PHAK Ch. 8):

• Pitot ram inlet blocked, drain hole open — airspeed falls toward zero, because the dynamic pressure bleeds out the drain.
• Pitot inlet and drain blocked (e.g., ice) — the trapped pressure makes the ASI behave like an altimeter: it reads high in a climb and low in a descent. This is the dangerous one, because the number still moves and looks plausible. Pitot heat is both the cure and the preventer.
• Static port blocked — the altimeter freezes at the blockage altitude, the VSI sticks near zero, and the ASI reads off the stale static reference. The fix is the alternate static source; selecting it (cabin pressure) typically makes the altimeter jump slightly and reads a touch high — a known, harmless quirk.

The unifying lesson: a single odd instrument is a cross-check problem, not a control problem. Confirm against the others, identify the failure, fly pitch-and-power, and don't chase a needle that's lying to you.

<CFR id="91.7" /> sits under all of this — the PIC is responsible for determining the airplane is fit for flight and must discontinue when an unairworthy condition appears in flight. Recognizing which malfunction you have is the first half of that judgment; the response (S1) and the land-or-continue decision (R2) are the second.