Definition
A gradual process in which a group or organization comes to accept practices, procedures, or conditions that depart from established standards, until those departures are no longer recognized as departures. Each small deviation that does not produce an immediate bad outcome lowers the threshold for accepting the next one, so unsafe practice slowly becomes the new normal.
Plain English
When people keep doing something a little wrong and nothing bad happens, they stop seeing it as wrong. Over time, cutting corners becomes the standard way of doing things, and no one notices anymore.
Context Anchor
Seen in aviation safety, maintenance, crew resource management, and accident-prevention discussions.
Derivation
From 'normalize' (to make standard or accepted) and 'deviation' (a departure from a rule or standard). The term was popularized by sociologist Diane Vaughan in her study of the Challenger space shuttle accident, where engineers gradually came to accept O-ring damage that originally would have stopped a launch. The phrase helps because it names the slow drift itself, not just the individual rule-breaking.
Why Pilots Care
Unchecked normalization of deviation erodes safety margins and has contributed to multiple aviation accidents.
Analogy
It is like ignoring a warning light in a car because the car still drives fine. After a while, the warning feels less serious, even though the underlying risk has not gone away.
Intuition Check
Do not read this as a harmless change in routine. In aviation, normalization of deviation means an unsafe or unapproved practice has started to feel acceptable because it has not yet led to trouble.
Example Sentence 1
The flight school recognized a normalization of deviation when instructors realized that skipping the runup at a busy airport had quietly become routine.
Example Sentence 2
The accident report cited normalization of deviation as the reason the team no longer performed the required preflight check.