Instrument Flight: Aircraft General Knowledge (systems relevant to IFR flight)
What the exam tests
Aircraft General Knowledge for IFR concentrates on systems that affect instrument flight: pitot-static, gyroscopic and ADC sources, electrical power, ice protection, pressurisation and oxygen, autopilot and flight director, and warning systems. Expect system-failure effects, not maintenance detail.
Core rules
- The altimeter is a pressure instrument; it needs a correct QNH or QFE and an unobstructed static source.
- Airspeed depends on pitot pressure and static pressure; blockage effects differ between the two sources.
- Attitude and heading references may be gyroscopic, AHRS or ADC-derived; know what remains after a vacuum or power loss.
- Autopilot modes include altitude hold, vertical speed, IAS/Mach and glideslope; know what disconnects and what remains usable.
- Ice protection: pitot heat, static heat, airframe de-icing or anti-icing, and windshield heat are IFR-critical.
- Emergency power may feed a standby attitude indicator, battery bus and essential instruments.
Worked example
A blocked static port in level flight leaves the ASI reading like an altimeter, the VSI frozen at zero and the altimeter frozen. Pitot heat does not fix a static blockage. Select the alternate static source, expect ASI and altimeter errors, then use GPS, radio altitude and pitch attitude.
Traps
- Pitot blockage makes the ASI act as an altimeter; static blockage makes the ASI over-read in climb and under-read in descent.
- A vacuum failure affects gyros, not the ADC.
- Alternate static can introduce a small altitude error.
- Autopilot does not remove the need to monitor raw data.