IR.II.B.K1bFAA-S-ACS-8C · Nov 2023Knowledge
b. Gyroscopic/electric/vacuum instrument system and associated instruments
Operation of the aircraft’s applicable flight instrument system(s), including: b. Gyroscopic/electric/vacuum instrument system and associated instruments
Bottom line
It is important to monitor vacuum pressure during flight, because the attitude and heading indicators may not provide reliable information when suction pressure is low. It is important to ensure that mechanical gyroscopic instruments have adequate time to spool up to acceptable rpm in order for them to indicate properly. It is extremely important that pilots consult the POH/AFM to determine the power source of all instruments, so they know what action to take in the event of an instrument failure.
Key numbers
| Number | What it means |
|---|---|
| typically 4.8 to 5.2 in. Hg at 2,000 rpm (check AFM/POH) | Vacuum level |
| three-phase 115-volt, 400-Hz A.C. from 14 or 28 volts D.C. | Inverter output |
FAA references
- 14 CFR 91.205 (Powered civil aircraft with standard U.S. airworthiness certificates: Instrument and equipment requirements.) — eCFR current as of 2026-03-05
- PHAK ch. 8 (p. 8-16) — FAA-H-8083-25C (2023)
- AFH ch. 2 (pp. 2-21–2-22) — FAA-H-8083-3C
- IFH ch. 5 (pp. 5-17–5-19) — FAA-H-8083-15B
- RMH ch. 1 (p. 1-2) — FAA-H-8083-2A
Build understanding you can use
Unlock the full lesson and continue studying this element.
- Full teaching sections: What it is; Key points; Rules and numbers; How it is done
- Check your understanding with answers you can reveal
- Common mistakes paired with the FAA facts that correct them