- An act or condition that singly, or in combination with other causes, results in the damage or injury that occurred,
- A deficiency that, if corrected or eliminated or avoided, would have likely prevented or mitigated the accident damage or significant injuries
- An act, an omission, a condition, or a circumstance that either starts or sustains an accident sequence.
Conditions that facilitate errors by frontline operators but which are outside of the direct control of frontliners.
- Almost all accidents are "multicausal", meaning that more than one cause produced the event. If we only focus on a single cause, then it will usually involve the pilot, who might be dead and cannot do anything to prevent a future accident.
- Effective investigations are those that provide recommendations to deal with the root causes, since those are the recommendations that can best prevent other accidents. Recommendations crafted around active causes actually often just deal with the crew and thus often will not prevent future accidents.
- Since accidents result from more than one cause, it is often suggested that we should not prioritize the causes. Nevertheless, people often want to know what the "primary" or "trigger" cause was for an accident.