What might have been a catastrophe in New York — one that evoked the feel if not the scale of the Sept. 11 attack — was averted by a pilot’s quick thinking and deft maneuvers, and by the nearness of rescue boats, a combination that witnesses and officials called miraculous.
请问句中的if not该怎么理解呢（结合整个句子，破折号中间这部分怎么翻译）？ 根据字典if not意思有：要不, 不然；如果不；除非，如果不；否则。但是好像直接带到句子里都不太合适。
请教英语高手~~~万分感谢~~