Threat and Error Management is based on work done at the University of Texas. Unlike previous approaches it is based on observations by researchers riding along with crew is aircraft cockpits. As a result it takes into account threats and errors that were handled successfully, not just the ones that led to incidents as with traditional research methods.
Errors in flight were found to be common:
One common false assumption is that errors and violations are limited to incidents and accidents. Recent data from Flight Operations Monitoring (e.g. LOSA) indicate that errors and violations are quite common in flight operations. According to the University of Texas LOSA database, in around 60% of the flights at least one error or violation was observed, the average per flight being 1.5.
It uses a system approach rather than seeking a person or persons to blame. The problem with the blame approach is that it stops short of understanding deeper causes.
Here’s an explanation of the system approach and the person approach:
Two approaches to the problem of human fallibility exist: the person and the system approaches
The person approach focuses on the errors of individuals, blaming them for forgetfulness, inattention, or moral weakness
The system approach concentrates on the conditions under which individuals work and tries to build defences to avert errors or mitigate their effects
High reliability organisations—which have less than their fair share of accidents—recognise that human variability is a force to harness in averting errors, but they work hard to focus that variability and are constantly preoccupied with the possibility of failure
In this system Threats are external factors such as adverse weather and Errors are caused by human actions or inactions.
Examples of undesired aircraft states include: off altitude, off airspeed, off course, and the wrong place at the wrong time. Managed effectively, pilots can restore margins of safety or if mismanaged could likely create additional error, an incident, or accident.
More terms are defined here;Flight Operations Briefing Notes Human Performance Error Management(pdf)