Emergency Locator Transmitters (ELT) must be inspected once every 12 calendar months for:
- Proper installation;
- Battery corrosion;
- Operation of the controls and crash sensor; and
- The presence of a sufficient signal radiated from its antenna.
The batteries must be replaced or recharged:
- When the transmitter has been in use for more than 1 cumulative hour; or
- When 50 percent of their useful life (or for rechargeable batteries, 50 percent of their useful life or charge) has expired, as established by the transmitter manufacturer under its approval.
A 1994 regulation change, 91.207(d), requires a separate sign-off or annual inspection for the ELT. The mechanic actually makes a separate log entry about the ELT. This usually will occur at the same time of the aircraft's annual inspection, but it doesn't have to. The unwary pilot in command could miss the timing on this inspection and find himself in the same trouble as if he had flown with an airworthiness directive compliance time missed. As we know, the mechanic's signature at an annual is a statement of condition at that time and does not guarantee that everything will remain airworthy until the next annual.