# Heading Indicator (HSI) - Uses a magnetometer (GMU 44) to measure the local magnetic field and display it on the PFD - Magnetometer is located on the left wing to avoid interference with other electrical components (right wing has the flap motor) # GMU 44 - from the G1000 Pilot's Guide ![[Pasted image 20240121115337.png]] ![[Pasted image 20240121115404.png]] # Magnetic Compass - One of the oldest and simplest instruments for indicating direction - Contains magnetic metal (typically iron) which align with the lines of magnetic flux from the earth - Subject to errors due to interference with the location of installation and dip caused by magnetic flux lines # Lines of Magnetic Flux ![[Pasted image 20240121115836.png]] # Inside of a Magnetic Compass ![[Pasted image 20240121120542.png]] # Magnetic Deviation - Interference caused by other cockpit instruments and electronics - Typically corrected for using a compensating magnet - Compass deviation cards can be used to correct for this error # Magnetic Dip - Magnetic flux lines point downwards when approaching the poles - This will cause the magnetic compass to dip towards the low side of a turn # Acceleration and Deceleration Errors - Acronym *ANDS* - Accelerate-North, Decelerate-South - This will be opposite in the southern hemisphere - Accelerate $\rightarrow$ Compass shows turn to the north - Decelerate $\rightarrow$ Compass shows a turn to the south # Turning Errors - Turn from a northerly heading $\rightarrow$ Compass initially indicates a turn in the opposite direction - *ONES*: Opposite North, Exaggerated South - When rolling out of a turn, you need to properly overshoot or undershoot based on your latitude - can use the acronym OSUN (overshoot south, undershoot north) ![[Pasted image 20240121115656.png]] # Calculating Overshoot or Undershoot $ H_C = atan2(sin(H_M)cos(\theta) - tan(\mu)sin(\theta), cos(H_M)) $ $\theta =$ bank angle $\mu =$ dip # Making Small Turns - Utilize timed turns when making small adjustments to heading solely by reference the the magnetic compass - This is especially useful when turning on a northerly or southerly heading