on the fly

John Grishamの小説 "Camino Island" を読み始めました。

Getting out of the country was imperative. That was not what he had planned, but things could not be lining up more perfectly. Plans--nothing ever goes as planned, and the survivors are the ones who can adapt on the fly.

"on the fly" を辞書で確認します。

・Oxford English Dictionary: if you do something on the fly, you do it quickly while something else is happening, and without thinking about it very much
・Merriam-Webster's Online Dictionary: in a hurry and often without preparation : HASTILY, SPONTANEOUSLY: making decisions on the fly
・Collins Dictionary:　If you do something on the fly, you do it quickly without thinking about it or planning it in advance, especially while something else is happening.： It was all pretty much done on the fly.
・Wiktionary: Spontaneously or extemporaneously; done as one goes, or during another activity.: The software program has a table of values for some results, but calculates others on the fly.