An emergency locator transmitter is normally activated by an inertial switch or equivalent mechanism when subjected to a force of prescribed intensity and duration. Which of the following is a valid activation mechanism?

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Automatic activation of an emergency beacon in a crash relies on sensing a sudden, large deceleration. An inertial switch does exactly that: it contains a mass or mechanism that responds when the g-forces exceed a preset threshold for a short time, closing the circuit and turning on the transmitter. This ensures the ELT activates even if the crew can’t reach a switch after impact.

A manual switch would require someone to act, which isn’t reliable in a crash scenario. A proximity sensor isn’t appropriate because there’s nothing to sense nearby to trigger the beacon. A temperature switch would respond to heat, not the crash-induced forces you want to detect. So the inertial switch is the correct activation mechanism.