FAA Instrument Rating Airplane (IRA)Flight Instruments and SystemsHard
A technician explains that a glass cockpit aircraft's Attitude and Heading Reference System (AHRS) uses solid-state sensors, such as ring laser or MEMS gyros and accelerometers, instead of traditional spinning-mass gyros. What is the primary operational advantage of this design?
- AAHRS has no moving parts subject to mechanical wear, erects faster after power-up, and is generally more reliable than vacuum-driven gyros
- BAHRS requires a vacuum pump for accuracy, providing built-in redundancy with mechanical gyros
- CAHRS eliminates the need for a magnetic compass correction card entirely
- DAHRS instruments are completely immune to all forms of precession error
Show answer & explanationAnswer & explanation
Correct answer: A. AHRS has no moving parts subject to mechanical wear, erects faster after power-up, and is generally more reliable than vacuum-driven gyros
Solid-state AHRS units use laser or MEMS-based sensing rather than spinning rotors, eliminating mechanical wear points such as bearings and gimbals, allowing faster alignment after startup and improving long-term reliability compared to vacuum-driven mechanical gyros.
Why the other options are wrong
- B. AHRS is electrically powered and does not use a vacuum pump.
- C. A compass correction card is still needed because magnetic deviation still affects heading references.
- D. AHRS still requires algorithms to correct for drift and errors; it is not immune to all error sources.
AHRS (Attitude and Heading Reference System)
A solid-state replacement for vacuum-driven gyros that uses laser or MEMS sensors and accelerometers to compute attitude and heading, offering greater reliability and faster alignment.
- No spinning mass or vacuum pump required
- Faster erection/alignment after power-up
- Feeds attitude/heading data to the PFD in glass cockpits
Memory trick: No spin, no wear, no vacuum — solid-state wins the reliability race.