Final answer:
In aircraft navigation, a level turn will cause the compass to lead. When turning towards the north, the compass shows a turn plus a few degrees, and when turning towards the south it shows a turn minus a few degrees. The compass needle orientation remains consistent when flying due west on the equator and making level turns.
Step-by-step explanation:
The question refers to the behavior of a compass in an airplane when making different types of turns. If you're in an airplane flying due west along the equator and looking at a compass while crossing the prime meridian you will initially see the compass needle perpendicular to the direction of motion, with the north pole of the needle pointing to your right. As you continue flying due west, the orientation of the compass needle will not change significantly as long as you remain on the equator because you are maintaining the same latitude and the direction of the Earth's magnetic field remains constant relative to your direction of flight.
In terms of the options given in the question on what kind of turn would cause the compass to lead, the correct answer is: c) Level turn. During a level turn, meaning you maintain the same altitude, the compass in an aircraft will show a lead or lag depending on the direction you are turning. Specifically, when turning to the north, the compass will temporarily show a turn in that direction plus a few degrees, which is known as a lead. When turning to the south, the compass will show a turn in that direction minus a few degrees, indicating a lag. When making a right or left turn on the equator, the needle might initially swing due to centrifugal force but would settle back to its original orientation if the level turn is maintained.