On-Scene Coordinator:

A person designated to co-ordinate SAR operations within a specified area.

If SMC is not designated OSC performs additional duties of SMC till thetimes SMC is deputed. Normally this duty carried out by ship master unlessmore capable SRU is available. Among its duties are: Receive search &rescue action plans from SMC or make them himself if no SMC is deputed. Make SITREPS. Coordinate on scene communications and operations of all SAR facilities.

More info : https://www.imrfmro.org/mro-library-command-control-coordination-download/file/945-4-4-the-on-scene-coordinator