Aircraft General Knowledge - Instrumentation
What the exam tests
Instrumentation covers pitot-static, gyroscopic, magnetic, EFIS and warning systems. Questions test interpretation and failure modes.
Core rules
- Pitot blocked: ASI behaves like an altimeter in climb/descent; static blocked: ASI overreads in climb, underreads in descent; altimeter freezes.
- Altimeter: 1 hPa ≈ 27 ft; QNH/QFE/1013 selection.
- Gyro: rigidity and precession; attitude indicator erection; turn coordinator shows rate, not bank angle.
- Magnetic compass: turning and acceleration errors; UNOS (undershoot north, overshoot south).
- EFIS: compare standby instruments; do not chase a single unreliable display.
Worked example
Climbing through FL200 with the static port blocked, the ASI indicates an increasing speed even though IAS is constant. The altimeter remains fixed at the altitude where the blockage occurred. The correct action is to use the standby/alternate static source, cross-check GPS ground speed and pitch/power, and declare the failure if needed. Reasoning: the ASI uses static pressure; trapped static pressure makes the instrument read altitude change as speed change.
Traps
Treating the turn coordinator as an attitude indicator; forgetting compass acceleration error; using QFE for flight levels; chasing an EFIS anomaly without cross-checking standby instruments; ignoring pitot heat in icing.