For "On-scene" communications, vessels in distress and SAR aircraft should use?

The correct choice for "On-scene" communications during emergencies involving vessels in distress and search and rescue (SAR) aircraft is centered around the use of designated frequencies. VHF Channel 16 is widely recognized as the international distress and calling frequency, making it an essential choice for initial communications concerning emergencies.

The inclusion of 4125 kHz is also significant as it is used for vessel-to-vessel and vessel-to-shore communications in the medium-frequency band, and J3E indicates single sideband (SSB) voice. This is especially useful for long-range communication beyond the line of sight that VHF may have limitations on. The use of the 3023 kHz frequency indicates another communication method, ensuring robust options for maintaining contact.

In summary, selecting VHF Channel 16 provides immediate access for calling and distress situations, while the other frequencies allow for continued communication as necessary. This combination maximizes the chances of effective communication during critical SAR operations.