Abnormal Systems: Partial Power and Pitot-Static Failures

A partial power loss or rough-running engine is a serious warning even when some power remains. The usual suspects are carburetor ice, a fouled spark plug, a failing magneto, or a fuel-system problem, and the pilot works through them methodically: carburetor heat for suspected ice, mixture and throttle adjustments, magneto checks, and switching fuel tanks — all while continuously planning for a possible forced landing in case the engine quits entirely. Pitot-static failures attack the instruments rather than the engine. If the pitot ram inlet is blocked but its drain hole stays open, the airspeed indicator drops toward zero; when BOTH the pitot opening and the drain hole are blocked, the trapped pressure makes the airspeed indicator behave like an altimeter, reading higher as you climb and lower as you descend. A blocked static port throws off the airspeed indicator, altimeter, and vertical speed indicator together. The fix is the alternate static source — and if the airplane has none, the traditional last resort, where the POH permits and teaches it, is to break the glass of the VERTICAL SPEED INDICATOR, the static instrument you can best do without, which opens the case to cabin static pressure (expect the VSI to then read reversed). Fly known pitch-and-power settings as a reliable backup while you sort out which instruments you can still trust — and remember the companion cue from the engine side: with a fixed-pitch propeller, carburetor ice first shows as a decrease in RPM.