Idiom
On the fly
If you do something on the fly, you do it quickly while something else is happening, without stopping to plan or prepare.
How people use it
People use it at work, in tech and in daily life: "We had to change the plan on the fly when the speaker got stuck in traffic." It suggests quick thinking and adjusting in the moment. In computing, data processed "on the fly" is handled as it arrives, while a program keeps running. It is close to "off the cuff," but "off the cuff" is mostly about speaking, while "on the fly" covers any action. The tone is informal to neutral, fine for most workplaces.
Examples
- The band forgot the set list, so they picked songs on the fly.
- Our teacher adjusted the lesson on the fly when the projector stopped working.
- This app translates speech on the fly, so travelers can chat with locals.
Where it comes from
The phrase probably comes from sports. In baseball, catching a ball "on the fly" means catching it while it is still in the air, before it bounces, a use recorded in American English in the 1800s. Older hunting language also spoke of shooting birds on the wing. The general sense of doing something while in motion, without stopping, grew from these pictures, and the computer sense arrived in the late 1900s.
Check yourself
1. What does it mean to make decisions on the fly?
Answer: To decide quickly as things happen. On the fly means in the moment, without stopping to plan first.
2. Which sentence uses the idiom correctly?
Answer: When the oven broke, Sam changed the dinner menu on the fly.. On the fly describes quick changes made while things are happening, not careful planning far ahead.
Similar idioms
Word game fan? See every word hiding in FLY.