The answer to the question above would be that the function of the underlined phrase is that it is a prepositional phrase acting as an adverbial phrase. That is, the correct option would be C.
An adverbial phrase is the term to refer to two or more words that play the role of an adverb. In this case, "during" introduces an adverbial phrase of time indicating the amount of time the pilot maneuvered successfully. Answer: during the (whole) training mission.
