What is the minimum operator license required to perform or supervise the performance of at-sea adjustments, servicing or maintenance which may affect the proper operation of the GMDSS station?

Correct Answer: Option D — GMDSS Radio Maintainer's license.

FCC rules mandate that at-sea maintenance or adjustments affecting GMDSS equipment performance must be performed by or under the direct supervision of a GMDSS Radio Maintainer. This license ensures the technician possesses the technical expertise required to maintain the integrity of critical distress and safety communication systems.