Doomsday Icarus
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"Never regret thy fall, O Icarus of the fearless flight, For the greatest tragedy of them all, Is never to feel the burning light."
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In the Northern Hemisphere, a magnetic compass will normally indicate initially a turn toward the west if...
In the Northern Hemisphere, if an aircraft is accelerated or decelerated, the magnetic compass will normally indicate...
In the Northern Hemisphere, a magnetic compass will normally indicate initially a turn toward the east if...
FAA Knowledge Test Prep
Summary
*Variation is caused by the change in Earth magnetic field around the Earth
*Deviation is caused by equipment in the aircraft affecting the compass reading
*In the northern hemisphere, turning away from a Northerly heading will momentarily indicate a turn in the opposite direction (North Opposite = NO)
*In the northern hemisphere, turning away from a Southerly heading will momentarily indicate a faster turn in the same direction (South Same = SS)
*In the northern hemisphere, a turn to a heading with a Northerly component will need to be undershot because the compass will lag (Undershoot North =UN of UNOS)
*In the northern hemisphere, turn to a heading with a Southerly component will need to be overshot because the compass will lead (Overshoot South =OS of UNOS)
*In the northern hemisphere, the compass will indicate a turn towards the north if the airplane is accelerated on a east or west heading
*There are no acceleration errors if flying on a north or south heading
*The compass is most accurate during straight and level flight
*TO VISUALIZE THIS: Think of what your head does on a rollercoaster. When the roller coaster shoots off your head is crammed back into the headrest of your seat. This is what happens to the needle of your compass except for your compass the headrest of your seat is the closest magnetic pole on Earth. So when you accelerate the needle gets pushed towards the closest pole. On the other side of things, when the roller coaster comes to an abrupt stop at the end of the ride your head lurches forward away from your seat. In your compass, this is your needle lurching away from the closest pole during a deceleration.
Pilots in the Northern Hemisphere remember this by the acronym A.N.D.S.;
Accelerate North, Decelerate South. Pilots in the Southern Hemisphere can use S.A.N.D.;
South Accelerate, North Decelerate.
• There is no effect when accelerating/decelerating on a heading of North or South
• If decelerating the compass will dip towards the farthest pole (to the South in northern hemisphere, to the North in southern)
Acceleration
While in unaccelerated straight-and-level flight there is no effect of magnetic dip or errors trom inertia. When the aircraft is accelerating or decelerating on an easterly or westerly heading there is an effect of both:
• If accelerating the compass will dip towards the closest pole (to the North in northern hemisphere, to the South in southern)
How much should you overshoot or undershoot?
The amount you should overshoot or undershoot actually changes depending on your final targeted heading.
When your final heading is directly North or South, the dip error is at its greatest. This maximum amount of overshoot or undershoot can be estimated by the latitude at which you are flying. For example, the image below depicts the undershoot and overshoot values someone can use when flying at a latitude of 30 degrees. The image shows that when the final heading is direct North, the pilot should undershoot the heading the maximum amount of 30 degrees.
If your heading is NOT direct North or direct South then you can estimate the amount of undershoot or overshoot using a fraction of your latitude. For example, if your final heading is 330 degrees at a latitude of 30 degrees than you can estimate your undershoot by 20 degrees. We use 20 degrees for a heading of 330 because 330 is 2/3 of the way between direct West and direct North so we are going to undershoot it by 2/3 of our maximum undershoot (which is our latitude of 30 degrees).
