Welcome Guest. Sign in or Signup

1 Answers

About that Slaving Control and Compensator Unit for the HSI

Asked by: 864 views , , , , , , , , ,
General Aviation

When do I ever need to switch from slave to free mode? I can't think of any other scenario except for the flux valve being inoperative or getting interference that will cause the compass card to read incorrectly. 

Ace Any FAA Written Test!
Actual FAA Questions / Free Lifetime Updates
The best explanations in the business
Fast, efficient study.
Pass Your Checkride With Confidence!
FAA Practical Test prep that reflects actual checkrides.
Any checkride: Airplane, Helicopter, Glider, etc.
Written and maintained by actual pilot examiners and master CFIs.
The World's Most Trusted eLogbook
Be Organized, Current, Professional, and Safe.
Highly customizable - for student pilots through pros.
Free Transition Service for users of other eLogs.
Our sincere thanks to pilots such as yourself who support AskACFI while helping themselves by using the awesome PC, Mac, iPhone/iPad, and Android aviation apps of our sponsors.

1 Answers



  1. Skyfox on Jul 30, 2016

    I’m not terribly familiar with the remote indicating compass system but I’ll try to help out (I’ve flown with an HSI before but it was gyro only, not the RIC style). With that system, when it’s in slave mode, the flux gate thing is sending information to the DG, HSI, or RMI for automatic alignment with magnetic north. If there’s an error between the magnetic compass and the HSI or whatever, put it in free mode to use the clockwise and counterclockwise buttons to adjust it, then put it back in slave mode. If the thing is just plain not working right, keep it in free mode so it acts as a standard heading indicator. In that case, the clockwise/counterclockwise buttons can be used to correct for precession just as you would when using the compass card adjustment knob.

    It’s described in chapter 5 of the Instrument Flying Handbook (FAA-H-8083-15B) but it’s clear as mud and could use some revision for a better explanation of how it works.

    +1 Votes Thumb up 1 Votes Thumb down 0 Votes


The following terms have been auto-detected the question above and any answers or discussion provided. Click on a term to see its definition from the Dauntless Aviation JargonBuster Glossary.

Answer Question

Our sincere thanks to all who contribute constructively to this forum in answering flight training questions. If you are a flight instructor or represent a flight school / FBO offering flight instruction, you are welcome to include links to your site and related contact information as it pertains to offering local flight instruction in a specific geographic area. Additionally, direct links to FAA and related official government sources of information are welcome. However we thank you for your understanding that links to other sites or text that may be construed as explicit or implicit advertising of other business, sites, or goods/services are not permitted even if such links nominally are relevant to the question asked.