Definition
A deviation from the originally planned or cleared route of flight, typically requested or directed to avoid hazardous weather, traffic, terrain, or restricted airspace, after which the aircraft rejoins its intended route.
Plain English
Going around something instead of straight through it, then getting back on your planned path. In flying, this usually means flying around a thunderstorm or area of bad weather rather than through it.
Context Anchor
Seen during weather avoidance, especially when a pilot asks air traffic control for help routing around thunderstorms or other unsafe areas.
Derivation
From the French détour, meaning 'a turning aside.' The Old French tourner means 'to turn,' with the prefix de- meaning 'away.' So a detour is literally 'a turning away' from the direct path -- which fits exactly how pilots use it: turning aside from the cleared route to avoid a hazard, then turning back.
Why Pilots Care
Enables safe flight continuation by keeping the aircraft clear of turbulence, icing, or convective activity that could lead to loss of control or structural damage.
Intuition Check
A detour is not the same as getting lost or wandering off course. In this context, it is a deliberate route change made to avoid something unsafe or unsuitable.
Example Sentence 1
The pilot requested a detour 20 miles south of course to avoid a line of thunderstorms.
Example Sentence 2
ATC cleared the aircraft for a short detour west of the weather cell before resuming the original route.