When must the ELT battery be replaced?

The replacement of the Emergency Locator Transmitter (ELT) battery must occur when it has been used for 1 cumulative hour or has reached 50% of its useful life. This requirement ensures that the ELT remains functional and reliable in the event of an emergency. These standards are outlined in regulations to guarantee that the ELT will operate correctly when needed.

The rationale behind this timing is based on the operational limitations of battery performance. As batteries age or are used, their efficiency can diminish, which could impair the ELT's ability to transmit distress signals. By establishing these specific criteria for battery replacement, manufacturers and regulatory bodies aim to maintain a high level of safety in aviation.

Other choices do not align with regulatory requirements. For example, replacing the battery only when the ELT malfunctions could lead to situations where a battery that may still be within its useful life is actually no longer reliable. Similarly, requiring replacement after installation or on a fixed schedule of every 12 months doesn't consider actual usage, which is crucial to ensuring the ELT is functional when it is absolutely needed.