How can an operator switch the ELT between the ON and ARM positions?

The correct way for an operator to switch the Emergency Locator Transmitter (ELT) between the ON and ARM positions is by using the ELT control switch. This switch is specifically designed for that purpose, allowing the operator to activate or deactivate the ELT as needed. In an emergency situation, being able to quickly switch the ELT to the appropriate setting is crucial for ensuring it transmits a distress signal, which can aid in search and rescue operations.

The other methods mentioned would not allow for a direct or effective means of switching the ELT’s operational mode. For example, using the backup UHF panel might not be related to the ELT function and thus would not accomplish the task. Similarly, turning off the AUX BAT or adjusting the main power switch does not directly change the ELT's operational status and could potentially disrupt other systems or power sources without effectively activating the ELT. Thus, the ELT control switch is specifically designated for the function in question, making it the correct answer.