Definition
A human-factors phenomenon in which individuals in a group feel less personal accountability for taking action because they assume someone else will. In aviation, it most commonly appears in multi-crew operations or shared-responsibility situations, where each person believes another pilot, controller, or crewmember is handling a task, and as a result the task is not done.
Plain English
When more than one person could act, each person is more likely to assume someone else will do it, so no one does. The bigger the group, the stronger this effect tends to be.
Context Anchor
Seen in crew coordination, flight training, maintenance, ramp operations, and emergency situations where more than one person could speak up or take action.
Derivation
From Latin diffundere, meaning 'to spread out or pour out.' The idea is that responsibility, instead of resting on one person, gets spread thinly across the group until no single person feels enough of it to act.
Why Pilots Care
It can cause critical delays or inaction during emergencies or abnormal situations when crew members or ground personnel each expect someone else to act.
Analogy
If several people see a spill on the floor, each may think someone else will clean it up. The more people present, the easier it is for each one to feel less personally responsible.
Intuition Check
Diffusion of responsibility does not mean people do not care. It means the duty to act feels less clear because responsibility seems shared by the group.
Example Sentence 1
During the incident review, the instructor pointed out that diffusion of responsibility caused both pilots to miss the descending altitude, since each assumed the other was monitoring it.
Example Sentence 2
On the ramp the line crew left a chock in place expecting the pilot to notice it, illustrating diffusion of responsibility on the ground.