What must be replaced every 12 months according to inspection requirements?

The correct answer pertains to the requirement for the emergency locator transmitter (ELT) battery. According to regulatory standards, specifically those established by the Federal Aviation Administration (FAA), the battery in an ELT must be replaced or recharged every 12 months to ensure that the device will function properly in case of an emergency. This regular maintenance is crucial for the overall safety of flight operations, as an operative ELT is critical for search and rescue operations.

In contrast, a magnetic compass, fuel gauge, and oil temperature gauge do not have such stringent replacement requirements at set intervals. While these instruments must be inspected and maintained to ensure proper functionality, they are not mandated to be replaced every year under inspection protocols. Instead, components like the magnetic compass may require calibration or checks during regular maintenance, and gauges are typically serviceable as needed, not on a fixed annual schedule.