General Aircraft Knowledge and IFR Systems
Systems that support IFR flight
Candidates must understand the aircraft systems that make IFR flight safe: pitot-static, gyroscopic instruments, magnetic compass, electrical power, autopilot/flight director, and the navigation and communication radios. For each, know the power source, failure indications, and the partial-panel consequences.
Pitot-static and gyroscopic instruments
The altimeter, airspeed indicator, and vertical speed indicator all use static pressure; the airspeed indicator also uses pitot pressure. A blocked pitot tube with an open drain produces airspeed that behaves like an altimeter; a blocked static port affects all three. Gyroscopic instruments are either vacuum-driven or electrically driven; know which is which in the aircraft type and what happens when the vacuum pump fails. The attitude indicator and heading indicator are usually vacuum or electrically driven; the turn coordinator is electrically driven.
Traps in questions
- Assuming a failed attitude indicator is the only consequence of vacuum failure - the heading indicator also fails.
- Confusing the magnetic compass errors: variation, deviation, dip errors (acceleration and turning).
- Forgetting that an autopilot disconnect can be caused by an electrical or pitot-static fault, not just a servo fault.
Worked rule of thumb
When a question describes a static port blockage, ask: which instruments use static pressure? All three of altimeter, ASI, and VSI. Then decide the direction of error: in a climb with a blocked static port, the altimeter freezes, the VSI reads zero, and the ASI over-reads.
Study approach
Draw a block diagram of pitot-static and gyroscopic systems and label the failure modes.