Rev Up and Soar: ACE the AMP Aviation Maintenance Technician Powerplant Exam 2025!

Once starter brushes are worn down to one-half of their original length, they should be replaced. This is because as the brushes are used, they gradually wear down and become less effective. The correct amount of wear down is one-half of the original length, as replacing them too early may result in unnecessary costs and replacing them too late may result in damage to the starter. Option B is incorrect as it suggests replacing the brushes at three-quarters of their original length, which would result in replacing them too early. Option C is also incorrect, as replacing the brushes at one-quarter of their original length is too early and may also result in unnecessary costs. Option D suggests replacing the brushes at two-thirds of their original length, which is still too early and may result in unnecessary costs. It is important to replace starter brushes at the correct time to ensure efficient functioning of the starter and to avoid additional expenses.