FAA Aviation Mechanic Airframe (AMA)Airframe Electrical and InstrumentsHard
A light twin-engine airplane is equipped with a vacuum-driven attitude indicator and heading indicator, along with an electrically driven turn coordinator. What is the primary reason manufacturers commonly design gyroscopic instrument panels using two different power sources in this manner?
- AIt reduces the overall weight of the instrument panel
- BVacuum-driven instruments cannot be certified for IFR flight
- CIt provides redundancy so a single power source failure does not disable all gyro instruments
- DElectric gyros are always more accurate than vacuum gyros
Show answer & explanationAnswer & explanation
Correct answer: C. It provides redundancy so a single power source failure does not disable all gyro instruments
Using both vacuum and electrical power sources for gyroscopic instruments provides system redundancy: if the vacuum pump fails, the electrically driven turn coordinator remains available, and if the electrical system fails, the vacuum-driven attitude and heading indicators continue operating, preserving some attitude/heading reference for the pilot.
Why the other options are wrong
- A. Weight reduction is not the design driver; redundancy and safety are.
- B. Vacuum-driven instruments are commonly certified and used for IFR flight; this statement is false.
- D. Accuracy is not inherently different between vacuum and electric gyros of similar design; this is not the reasoning.
Gyro Instrument Power Redundancy
A design practice of powering gyroscopic flight instruments from two independent sources (vacuum and electrical) so that failure of one source does not eliminate all attitude/heading references.
- Typical setup: vacuum-driven attitude/heading indicators, electric turn coordinator
- Protects against single-point failure of vacuum pump or electrical system
- Important for maintaining instrument reference during IFR flight
Memory trick: Don't put all your gyros in one power basket.