CAA NZ AME Instruments cheat sheet

Aircraft Instruments - Core Knowledge

• Pitot-static system: total pressure (pitot) feeds the airspeed indicator; static pressure feeds ASI, altimeter and VSI. A blocked static port causes ASI to over-read in climb and under-read in descent, altimeter to freeze, VSI to read zero after transient.

• Altimeter is a calibrated aneroid barometer: subscale set to QNH gives elevation above mean sea level; set to QFE gives height above the reference datum; set to 1013.25 hPa (29.92 inHg) gives pressure altitude for flight levels.

• VSI is a rate instrument: a calibrated capillary (leak) delays static pressure change so the capsule deflection is proportional to rate of climb/descent; inherent lag of several seconds means it indicates trend, not instantaneous rate.

• Airspeed colour arcs: white arc = flap operating range (VSO to VFE); green arc = normal operating range (VS1 to VNO); yellow arc = caution range (VNO to VNE); red radial = VNE.

• Magnetic compass: deviation is aircraft-borne error (compass swing corrects via deviation card); variation is angular difference between true and magnetic north at the location. UNOS: undershoot north, overshoot south when turning through north/south.

• Heading relationships: TRUE + Variation = MAGNETIC; MAGNETIC + Deviation = COMPASS. Apply variation east subtract, west add when converting true to magnetic.

• Gyroscopic principles: rigidity in space (rotor maintains its plane) and precession (applied force produces apparent motion 90 degrees later in direction of rotation).

• Pitot heat and static drain checks: pitot heat must be checked for current draw and function before flight in IMC; blocked pitot with drain open causes ASI to read as an altimeter (increases in climb, decreases in descent).

• Instrument range marking rules: ASI markings relate to approved flight envelope; altimeter requires adjustable subscale readable to 0.01 inHg or 1 hPa and barometric range covering expected operation.