What are helping verbs in a verb phrase she had heard the figure skaters were arriving?

In the verb phrase "had heard," "had" is the helping verb, while "heard" is the main verb. Helping verbs, also known as auxiliary verbs, assist the main verb in expressing tense, mood, or voice. In this case, "had" indicates that the action of hearing occurred in the past before another action. The phrase as a whole conveys that she received information about the arrival of the figure skaters.