FAA Ground School Practice Test

Under what conditions does the magnetic compass indicate correctly in the northern hemisphere when an aircraft is accelerated or decelerated?

1. On an east or west heading

2. On a north or south heading

3. At low altitude

4. During rapid climbs

The correct answer is: On a north or south heading

In the northern hemisphere, a magnetic compass indicates correctly primarily when the aircraft is on a north or south heading. This accuracy arises from how the magnetic compass functions relative to the Earth's magnetic field. When aligned with a north or south heading, the compass needle is directly oriented with the magnetic field lines, allowing for a straightforward reading. At these headings, acceleration or deceleration has less impact on the compass’s performance. Specifically, if an aircraft is accelerating while on a north heading, the compass may show a slight turn to the east. Conversely, if it is decelerating, the compass may show a turn to the west. However, when the aircraft is on an actual north or south heading, these effects are minimized, leading to greater accuracy. On east or west headings, however, the compass can be subject to significant errors during acceleration or deceleration, causing it to indicate in a direction that does not correspond to the aircraft’s actual heading. This discrepancy tends to increase the further away the aircraft is from the true north or south orientation. Conditions like low altitude or rapid climbs do not inherently affect the basic function of the magnetic compass as closely as the orientation related to the Earth's magnetic field. Thus, while some factors might influence compass behavior under certain conditions