phrase. If you say that something will happen if necessary, when necessary, or where necessary, you mean that it will happen if it is necessary, when it is necessary, or where it is necessary. If necessary, the airship can stay up there for days to keep out of danger. At the start of a sentence, use a comma after "if necessary", "if needed", "when required", "where needed", etc. Normally, we don't need a comma before "if necessary", "when needed", etc. in mid-sentence or at the end of the sentence. Vay Nhanh Fast Money.

if necessary or when necessary