Is this relative clause correct? [closed]

I came across the following weird restrictive relative clause in which 'of which' is used in place of 'whose'. Actually, l am not quite sure whether it is correct or not.

The plane (the right engine of which broke down) has been repaired in Cairo Airport.

I don't know of any reason why that sentence should be considered syntactically incorrect in formal written English. "Of which" is not a very natural start to a relative clause, but it is an acceptable one in this kind of English: it uses the relative pronoun which, which can stand for an inanimate noun phrase like "the plane", and the preposition "of". The preposition comes before the relative pronoun because of what linguists call "pied-piping". There are some restrictions on pied-piping, but I don't think this sentence violates any of them. Maybe some speakers/writer have stricter restrictions on pied-piping in this context than I do.

If you convert it to separate sentences, it makes sense and is clearly grammatical:

(The right engine of the plane broke down.) The plane has been repaired in Cairo Airport.

The phrase "of which" is usually used in non-defining or non-essential relative clauses, which are offset by commas, and which are not essential to identifying the particular antecedent.

If the context of the sentence makes it clear what particular plane is being referred to, the sentence is correct if you add the commas:

The plane, the right engine of which broke down, has been repaired in Cairo Airport.

However, if knowing that the right engine broke down is in fact essential to identifying the plane in question, the relative clause is essential, and must use a relative pronoun (which will require some rewording):

The plane whose right engine broke down has been repaired in Cairo Airport.

The plane which had a broken-down right engine has been repaired in Cairo Airport.