What is meant by an accident error chain and how does this affect the accident investigator's efforts?

Answer 1

The accident error chain is usually a series of small events that led up the mishap. And, "but for" one of those events then the accident might not have occurred. Because of so many daily actions and fast paced events, error chains are sometimes tough to see before the accident. This is why a proactive safety program is so important. That way we don't rely on blood priority to change out an error routine. After a complete and detailed mishap investigation the error chain events become painfully clear. Your job as an investigator is to look beyond the words "pilot error" and discover all factors that might have created the mishap. We must always ask, "why did a supposedly qualified and trained crew make an error?" The words "pilot or maintenance" error tell us nothing! Always find OUT WHY!!

A comprehensive investigation may find other issues not related to the mishap, but could be a factor for another type of mishap. We may discover training issues, non-mishap related fatigue issues, maintenance issues, or ATC problems.

We say "Probable Cause", as we were not there at the instant the event became a mishap. So, we can't say with 100% proof that the probable cause was "THE" cause. (Now, that's a PEARL for a test!)

We do use "probable cause" as the event that created the mishap. Example: Say an airliner executed a landing with excessive speed and the pilot lost control and ran off the runway. The accident is within that sequence of events where, by NTSB definition of an accident, it became a reality. In this case, it's where damage or injury equated to NTSB 830 Accident definition.

OK, in the above scenario we find nothing wrong with the plane, etc. but we discover the pilot was very fatigued and tired. Well, the probable cause was an excessive airspeed and a failure to properly maintain control of the aircraft. NOW, at that point we would investigate further and try to discover why the pilot was fatigued. Maybe, the PIC was rushed, sick, a CRM issue, weather or ATC issues etc. Or, all of these little things became the error chain that lead to an irreversible error. Anybody recall the

American 1491(?) flight where the aircraft ran off the runway and crashed. Read that report. Anyway, in our original scenario those contributing factors notwithstanding, the "probable cause" was the failure to maintain positive control. Alas, if the PIC had not lost control and had gotten the

plane stopped, then there would have only been smoking tires and no accident, maybe. As you might suspect probable cause and contributing causes can be a little confusing and overlapping. So, there's some basic concepts good for either aircraft accident or homicide investigations.