Information gathered from SKYbrary
Threat and error management (TEM) is an overarching safety concept regarding aviation operations and human performance. TEM is not a revolutionary concept, but one that has evolved gradually as a consequence of the constant drive to improve the margins of safety in aviation operations through the practical integration of human factors knowledge.
TEM was developed as a product of collective aviation industry experience. Such experience fostered the recognition that past studies and, most importantly, operational consideration of human performance in aviation had largely overlooked the most important factor influencing human performance in dynamic work environments: the interaction between people and the operational context (i.e., organizational, regulatory and environmental factors) within which people discharged their operational duties.
The recognition of the influence of the operational context in human performance further led to the conclusion that study and consideration of human performance in aviation operations must not be an end in itself. In regard to the improvement of margins of safety in aviation operations, the study and consideration of human performance without context address only part of a larger issue. TEM therefore aims to provide a principled approach to the broad examination of the dynamic and challenging complexities of the operational context in human performance, for it is the influence of these complexities that generates consequences directly affecting safety.
TEM in Flight Operations
There are three basic components in the TEM model, from the perspective of flight crews: threats, errors and undesired aircraft states (UAS). The model proposes that threats and errors are part of everyday aviation operations that must be managed by flight crews, since both threats and errors carry the potential to generate undesired aircraft states. Flight crews must also manage undesired aircraft states, since they carry the potential for unsafe outcomes. Undesired state management is an essential component of the TEM model, as important as threat and error management. Undesired aircraft state management largely represents the last opportunity to avoid an unsafe outcome and thus maintain safety margins in flight operations.
- Threats—generally defined as events or errors that occur beyond the influence of the line personnel, increase operational complexity and which must be managed to maintain the margins of safety. During typical flight operations, flight crews have to manage various contextual complexities. Such complexities would include, for example, dealing with adverse meteorological conditions, airports surrounded by high mountains, congested airspace, aircraft malfunctions, errors committed by other people outside of the cockpit, such as air traffic controllers, flight attendants or maintenance workers, and so forth. The TEM model considers these complexities as threats because they all have the potential to negatively affect flight operations by reducing margins of safety.
Anticipated Threats
Some threats can be anticipated since they are expected or known to the flight crew. For example, flight crews can anticipate the consequences of a thunderstorm by briefing their response in advance, or they can prepare for a congested airport by making sure they keep a watchful eye for other aircraft as they execute the approach.
Unexpected Threats
Some threats can occur unexpectedly, such as an in-flight aircraft malfunction that happens suddenly and without warning. In this case, flight crews must apply skills and knowledge acquired through training and operational experience.
Latent Threats
Lastly, some threats may not be directly obvious to or observable by flight crews immersed in the operational context and may need to be uncovered by safety analysis. These are considered latent threats. Examples of latent threats include equipment design issues, optical illusions or shortened turn-around schedules.
Regardless of whether threats are expected, unexpected or latent, one measure of the effectiveness of a flight crew’s ability to manage threats is whether threats are detected with the necessary anticipation to enable the flight crew to respond to them through deployment of appropriate countermeasures.
Threat management is a building block to error management and undesired aircraft state management. Although the threat–error linkage is not necessarily straightforward, although it may not always be possible to establish a linear relationship or one-to-one mapping between threats, errors and undesired states, archival data demonstrate that mismanaged threats are normally linked to flight crew errors, which, in turn, are oftentimes linked to undesired aircraft states. Threat management provides the most proactive option to maintain margins of safety in flight operations by voiding safety compromising situations at their roots. As threat managers, flight crews are the last line of defense to keep threats from impacting flight operations.
Table 1 presents examples of threats, grouped under two basic categories derived from the TEM model. Environmental threats occur due to the environment in which flight operations take place. Some environmental threats can be planned for, and some will arise spontaneously, but they all have to be managed by flight crews in real time. Organizational threats, on the other hand, can be controlled (i.e., removed or at least minimized) at the source by aviation organizations. Organizational threats are usually latent in nature. Flight crews still remain the last line of defense, but there are earlier opportunities for these threats to be mitigated by aviation organizations themselves.
| Environmental Threats |
Organizational Threats |
|---|---|
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- Errors—generally defined as actions or inactions by the line personnel that lead to deviations from organizational or operational intentions or expectations. Unmanaged and/or mismanaged errors frequently lead to undesired states. Errors in the operational context thus tend to reduce the margins of safety and increase the probability of an undesirable event.
Errors can be spontaneous (i.e., without direct linkage to specific, obvious threats), linked to threats or part of an error chain. Examples of errors would include the inability to maintain stabilized approach parameters, executing a wrong automation mode, failing to give a required callout or misinterpreting an air traffic control (ATC) clearance.
Regardless of the type of error, an error’s effect on safety depends on whether the flight crew detects and responds to the error before it leads to an undesired aircraft state and to a potential unsafe outcome. This is why one of TEM’S objectives is to understand error management (i.e., detection and response) rather than to solely focus on error causality (i.e., causation and commission). From a safety perspective, operational errors that are timely detected and promptly responded to (i.e., properly managed) do not lead to undesired aircraft states, do not reduce margins of safety in flight operations, and thus become operationally inconsequential. In addition to its safety value, proper error management represents an example of successful human performance, presenting both learning and training value.
Capturing how errors are managed is then as important, if not more important, than capturing the prevalence of different error types. It is of interest to capture if and when errors are detected and by whom, the response(s) upon detecting errors and the outcome of errors. Some errors are quickly detected and resolved, thus becoming operationally inconsequential, while others go undetected or are mismanaged. A mismanaged error is defined as an error that is linked to or induces an additional error or undesired aircraft state.
Table 2 presents examples of errors, grouped under three basic categories derived from the TEM model. In the TEM concept, errors have to be “observable,” and the TEM model therefore uses the “primary interaction” as the point of reference for defining the error categories.
The TEM model classifies errors based upon the primary interaction of the pilot or flight crew at the moment the error is committed. Therefore, in order to be classified as aircraft handling error, the pilot or flight crew must be interacting with the aircraft (e.g., through its controls, automation or systems). In order to be classified as procedural error, the pilot or flight crew must be interacting with a procedure (e.g., checklists; Standard Operating Procedures (SOPs); etc.). In order to be classified as communication error, the pilot or flight crew must be interacting with people (ATC; ground crew; other crewmembers; etc.).
Aircraft handling errors, procedural errors and communication errors may be unintentional or involve intentional non-compliance. Similarly, proficiency considerations (i.e., skill or knowledge deficiencies, training system deficiencies) may underlie all three error categories. In order to keep the approach simple and avoid confusion, the TEM model does not consider intentional non-compliance and proficiency as separate categories of error, but rather as subsets of the three major error categories.
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Aircraft handling errors |
Manual handing/flight controls: vertical/lateral and/or speed deviations, incorrect flaps/speedbrakes, thrust reverser or power settings. Automation: incorrect altitude, speed heading, autothrottle settings, incorrect mode executed, incorrect entries. Systems/radio/instruments: incorrect packs, incorrect anti-icing, incorrect altimeter, incorrect fuel switches settings, incorrect speed bug, incorrect radio frequency dialled. Ground navigation: attempting to turn down wrong taxiway/runway, taxi too fast, failure to hold short, missed taxiway/runway. |
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Procedural errors |
SOPs: failure to cross-verify automation inputs. Callouts: omitted/incorrect callouts. Briefings: omitted briefings; items missed. Documentation: wrong weight and balance, fuel information, ATIS or clearance information recorded, misinterpreted items on paperwork; incorrect logbook entries, incorrect application of MEL procedures. |
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Communication errors |
Crew to external: missed calls, misinterpretations of instructions, incorrect read-back, wrong clearance, taxiway, gate or runway communicated. Pilot to pilot: within crew miscommunication or misinterpretation. |
- Undesired states—generally defined as operational conditions where an unintended situation results in a reduction in margins of safety. Undesired states that result from ineffective threat and/or error management may lead to compromised situations and reduce margins of safety aviation operations. This is often considered the last stage before an incident or accident.
Examples of undesired aircraft states would include lining up for the incorrect runway during approach to landing, exceeding ATC speed restrictions during an approach or landing long on a short runway requiring maximum braking. Events such as equipment malfunctions or ATC controller errors can also reduce margins of safety in flight operations, but these would be considered threats. Undesired states can be managed effectively, restoring margins of safety, or flight crew response(s) can induce an additional error, incident or accident.
Table 3 presents examples of undesired aircraft states, grouped under three basic categories derived from the TEM model.
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Aircraft handling |
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Ground navigation |
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Incorrect aircraft configurations |
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An important learning and training point for flight crews is the timely switching from error management to undesired aircraft state management. An example would be as follows: a flight crew selects a wrong approach in the flight management computer (FMC). The flight crew subsequently identifies the error during a crosscheck prior to the final approach fix (FAF). However, instead of using a basic mode (e.g., heading) or manually flying the desired track, both flight crew become involved in attempting to reprogram the correct approach prior to reaching the FAF. As a result, the aircraft “stitches” through the localizer, descends late and goes into an unstable approach. This would be an example of the flight crew getting "locked in" to error management rather than switching to undesired aircraft state management. The use of the TEM model assists in educating flight crews that, when the aircraft is in an undesired state, the basic task of the flight crew is undesired aircraft state management instead of error management. It also illustrates how easy it is to get locked into the error management phase.
Also, from a learning and training perspective, it is important to establish a clear differentiation between undesired aircraft states and outcomes. Undesired aircraft states are transitional states between a normal operational state (i.e., a stabilized approach) and an outcome. Outcomes, on the other hand, are end states, most notably reportable occurrences (i.e., incidents and accidents). An example would be as follows: a stabilized approach (normal operational state) turns into a destabilized approach (undesired aircraft state) that results in a runway excursion (outcome).
The training and remedial implications of this differentiation are of significance. While at the undesired aircraft state stage, the flight crew has the possibility, through appropriate TEM, of recovering the situation, returning to a normal operational state, thus restoring margins of safety. Once the undesired aircraft state becomes an outcome, recovery of the situation, return to a normal operational state and restoration of margins of safety is not possible.
Countermeasures
Flight crews must, as part of the normal discharge of their operational duties, employ countermeasures to keep threats, errors and undesired aircraft states from reducing margins of safety in flight operations. Examples of countermeasures would include checklists, briefings, callouts and SOPs, as well as personal strategies and tactics. Flight crews dedicate significant amounts of time and energies to the application of countermeasures to ensure margins of safety during flight operations. Empirical observations during training and checking suggest that as much as 70 % of flight crew activities may be countermeasures-related activities.
All countermeasures are necessarily flight crew actions. However, some countermeasures to threats, errors and undesired aircraft states that flight crews employ build upon “hard” resources provided by the aviation system. These resources are already in place in the system before flight crews report for duty and are therefore considered as systemic-based countermeasures. The following would be examples of “hard” resources that flight crews employ as systemic-based countermeasures:
- Airborne Collision Avoidance System (ACAS);
- Ground Proximity Warning System (GPWS);
- Standard operation procedures (SOPs);
- Checklists;
- Briefings;
- Training;
- Etc.
Other countermeasures are more directly related to the human contribution to the safety of flight operations. These are personal strategies and tactics, individual and team countermeasures, that typically include canvassed skills, knowledge and attitudes developed by human performance training (most notably by crew resource management [CRM] training). There are basically three categories of individual and team countermeasures:
- Planning countermeasures: essential for managing anticipated and unexpected threats;
- Execution countermeasures: essential for error detection and error response;
- Review countermeasures: essential for managing the changing conditions of a flight.
Enhanced TEM is the product of the combined use of systemic-based and individual and team countermeasures. Table 4 presents detailed examples of individual and team countermeasures.
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Planning Countermeasures |
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SOP briefing |
The required briefing was interactive and operationally thorough |
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Plans stated |
Operational plans and decisions were communicated and acknowledge |
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Workload assignment |
Roles and responsibilities were defined for normal and non-normal situations |
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Contingency management |
Crew members developed effective strategies to manage threats to safety |
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Execution Countermeasures |
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Monitor/cross-check |
Crew members actively monitored and cross-checked systems and other crew members |
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Workload management |
Operational tasks were prioritized and properly manages to handle primary flight duties |
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Automation management |
Automation was properly managed to balance situational and/or workload requirements |
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Review Countermeasures |
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Evaluation/modification of plans |
Existing plans were reviewed and modified when necessary |
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Inquiry |
Crew members asked questions to investigate and/or clarify current plans of action |
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Assertiveness |
Crew members stated critical information and/or solutions with appropriate persistence |
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