Pilot Exam Coach

US Private Pilot

Switch to Canada PSTAR
Aircraft systems and instrumentsQuestion 552 of 934

Why do most aircraft have at least two sources of power for the gyroscopic instruments?

  1. To make the gyros spin faster at high altitude
  2. To keep one source of bank information if another fails
  3. To reduce the need for a magnetic compass in flight
  4. To reduce engine load during a long cruise flight
Show answer

Correct answer: To keep one source of bank information if another fails

For example, the vacuum system can power the attitude indicator while the electrical system powers the turn coordinator.

Source: Pilot's Handbook of Aeronautical Knowledge (FAA-H-8083-25C), Chapter 8: Flight Instruments — Gyroscopic Flight Instruments — Sources of Power, page 218

Practice aircraft systems and instruments

Questions last reviewed: 18 October 2026