Magnetic compass Flashcards
Magnetic compass
- North Seeking Compass, which points to the MAGNETIC NORTH.
- Parts
– Pointer
– Compass
– Magnetic Deviation Card
True north
True North is the geographic north, drawing a line 90 degrees perpendicular from the equator towards the North.
Magnetic north
Magnetic North is which the compass references to.
Magnetic variation
The difference of true north and magnetic north
- Maps are drawn oriented to the True North
Compasses are oriented to the Magnetic North
The “difference” in degrees between the two is known as Magnetic Variation
Magnetic Variation is shown on maps
Two types of magnetic variation
Variation to the East
* If a map indicates an “E” variation, subtract the variation from the TRUE HEADING.
Variation to the West
* If a map indicates a W variation, add the variation to the TRUE HEADING.
- “East is Least; West is Best”
Magnetic deviation
- Interference caused by metallic objects in the aircraft panel.
- Cause a certain amount of inaccuracy in the magnetic compass
- A Compass Card is provided to show correction for errors
ACCELERATION AND DECELERATION ERRORS
- LOCATION: Northern or Southern Hemisphere
- HEADING: Easterly or Westerly (Directions other than North or South)
- CONDITION: Changing speed
- EFFECT: False indication of a turn
Remember the mnemonic:
* Northern Hemisphere: “ANDS” – Accelerate North Decelerate South
- Southern Hemisphere: “SAND” – South Accelerate North Decelerate
Turning errors
- LOCATION: Northern or Southern Hemisphere
- INITIAL HEADING: Northerly or Southerly
- CONDITION: Changing direction
- EFFECT: Indication lags/leads
Remember the mnemonics:
* Northern Hemisphere “UNOS” – Undershoot North, Overshoot South
- Southern Hemisphere “NOSE” – North Overshoot, South Early(Undershoot)
Important notes on operation
- Compass moves in the opposite direction of the turn.
- Always calculate for magnetic variation
- Check the compass card for magnetic deviation
- Compass is only 100% accurate in straight and level, un-accelerated flight.
- Keep metallic objects or magnets away from the MC.
Detecting failures
- Bubbles inside the Magnetic Compass
- Liquid level in the compass is below standard
- There is a leak in the compass housing
- There is no movement on the compass face when turning.
Turning error correction
- The amount of correction depends on LATITUDE and ANGLE OF BANK
- With 15 – 18 degree bank – the amount of lag and lead approximately matches your latitude plus one half of angle of bank you lead the roll out
– EXAMPLE: AT 25 DEGREE NORTH LATITUDE AND 16 DEGREE BANK:– A RIGHT TURN TO THE NORTH requires a ROLL Out of 327 degree– A RIGHT TURN TO THE SOUTH requires ROLL Out of 197 degre
