What is the primary precaution of the ELT A/B?

The primary precaution of the ELT A/B is that it should not be submerged under water for extended periods. This is important because while the Emergency Locator Transmitter (ELT) is built to be durable, prolonged exposure to water can compromise its functionality. Extended submersion may lead to water damage, impairing the device's ability to transmit distress signals effectively in an emergency situation.

Considering the other options, stating that the ELT is designed for underwater operation misrepresents its intended use. It is not primarily intended for underwater deployment, but more as an aerial signaling device in emergencies. Saying it can remain underwater indefinitely contradicts the necessity of maintenance and functionality, which would degrade with long-term water exposure. Finally, while a battery check before use is an important aspect of ensuring the ELT is operational, it does not directly relate to its operational limitations concerning water exposure.