(Not a teacher)
I would say it is an adverbial of place.
I can see why it has caused you confusion, however - the verb 'be' makes it seem like a complment rather than an adverbial, that is, describing 'the plane'.
It's best to see what someone with a better knowledge of grammar says, but I think its an adverbial phrase:
'Where is the plane?'
'The plane/It is near the other plane'
EDIT - I don't know if the term 'complement' is used in US terminology. I know that 'copula' isn't really used, and 'linking verb' is preferred, so perhaps there is another word for 'complement', which is closely linked to copular (linking) verbs.