Aircraft compasses are arguably one of the most important features of an aircraft. Proper navigation is needed to provide safe and smooth flight. Due to a handful of factors that cause a compass to drift over time, calibration of a sight compass is necessary. By calibrating a sight compass, many compass errors can either be avoid or fixed.
WHEN TO CALIBRATE
Sight compasses should undergo calibration on the following occasions:
- Before and after a new part is installed, removed or repaired.
- After a compass has experienced shock from a difficult landing or rough turbulence.
- If the aircraft has flown through an electrical storm or has been struck by lightning.
- Whenever flux valves have been replaced.
- When aircraft operation has to change due to a new location with a large change in magnetic deviation.
- If the compass accuracy is being questioned.
Notably, a sight compass should be calibrated whenever an inaccuracy is detected. Inaccuracies can occur from the following:
IMPROPER INSTALLATION & VIBRATION
Compass installation errors can be avoid if the sight compass is properly calibrated before and after installation. Many manufacturer manuals instruct individuals to calibration a sight compass after installation to ensure accuracy of compass deviation and variation.
This inaccuracy mainly results from magnetism from unexpected sources. These sources are considered either hard magnetic parts or soft magnetic parts.
Hard magnetic parts, also known as hard iron, refer to aircraft parts that have constant magnetism. To fix this error, the sight compass has to either be recalibrated or go through a compass swing procedure. During either procedure, a compensating magnet may be used. This method will restore the sight compass to its original and accurate state as long as the magnetism does not change again.
When dealing with soft magnetic parts, also known as soft iron, a variable magnetism is present. This type of magnetism will cause sight compass deviation. Due to the compass deviation, use of a compensating magnet is not possible.
To ensure your sight compass is operating to its fullest, be sure to calibrate the instrument regularly. Frequent calibration of any instrument can administer a sense of confidence by ensuring accuracy and safety.