Human factors in aviation is the study of how people perform, and where their limits lie, in maintenance and flight operations, in relation to procedures, equipment, the working environment and other people. The aim is not to pin an error on an individual but to make visible the conditions that produce it. The US Federal Aviation Administration's (FAA) maintenance technician handbook states that it is universally agreed that human factors are involved in 80 percent of maintenance errors.
In Europe and in Türkiye this is a training obligation. The Part-145 rules of the European Union Aviation Safety Agency (EASA) require the competence of maintenance organisation staff to include human factors and human performance; according to the acceptable means of compliance, recurrent training is delivered in each two-year period. The SHT-145 instruction of Türkiye's Directorate General of Civil Aviation (SHGM), which governs approved maintenance organisations in the country, follows the same line.
In short:
- Dirty Dozen: the 12 conditions that most often lead to maintenance errors; a separate topic in EASA's maintenance licence syllabus.
- SHELL model: a model that places the person at the centre and examines the interfaces with software, hardware, environment and other people; it appears in ICAO's Safety Management Manual (Doc 9859).
- Part-145 training: initial training before starting work, then recurrent training every two years (EASA, SHGM SHT-145).
Why do human factors matter so much in aviation?
SHGM's SHT-145 defines human factors as principles that aim for a safe interface between people and other system components while fully taking human performance into account. The FAA handbook makes this concrete for maintenance: parts installed incorrectly, missing parts, required checks not performed.
According to the handbook, maintenance errors are harder to detect than many other safety threats; they are often present but invisible and can remain latent, affecting the aircraft's operation for long periods. Working conditions add to the risk: night or early-morning shifts, confined spaces, high platforms, and varying temperature and humidity. That is why human factors is treated as a competence area in its own right, alongside technical skill.
What is the Dirty Dozen and what are the 12 items?
According to the FAA handbook, after a large number of maintenance-related accidents and incidents in the late 1980s and early 1990s, Transport Canada identified twelve factors that degrade people's ability to work effectively and safely. Known as the "Dirty Dozen," the list was adopted by the industry as a straightforward way to talk about human error in maintenance. In EASA's Part-66 licence syllabus, item 9.10 of Module 9 is devoted to "the Dirty Dozen and risk mitigation."
| Factor | What it means |
|---|---|
| Lack of communication | Information needed to complete a task is not passed on, or only partly |
| Complacency | Overconfidence from repetition; seeing what you expect to see |
| Lack of knowledge | Shortage of training, information or ability |
| Distraction | Anything that draws attention away from the task |
| Lack of teamwork | Failure to work together towards a shared goal |
| Fatigue | Physical or mental exhaustion that threatens performance |
| Lack of resources | Not enough people, equipment, documentation, time or parts |
| Pressure | Real or perceived demands for high performance |
| Lack of assertiveness | Failure to voice concerns about instructions or others' work |
| Stress | A factor causing physical or mental tension |
| Lack of awareness | Failure to recognise a situation and foresee its outcome |
| Norms | Expected but unwritten rules of behaviour |
The FAA Safety Team poster suggests simple countermeasures for each item, among them using checklists, going back three steps when restarting interrupted work, not signing for work you did not do, working from current manuals and ordering parts before they are needed.
What is the SHELL model and how is it used in aviation?
The 2009 second edition of ICAO's Doc 9859 Safety Management Manual describes the SHEL (or SHELL) model as a simple yet visually powerful conceptual tool for analysing how people interact with their operational context. Its name comes from the initials of its four components:
- S (Software): procedures, training, supporting documents.
- H (Hardware): machines and equipment.
- E (Environment): the circumstances in which the system operates.
- L (Liveware): the people in the workplace.
At the centre of the model are the people at the front line; the second "L" stands for their relationships with other people. ICAO notes that humans are not as standardised as hardware, so the effects of mismatches at the interfaces must be understood and other components matched to people. The manual also warns that people tend to adapt to hardware mismatches, which can mask serious deficiencies until an occurrence reveals them.
The UK Civil Aviation Authority's CAP 716 guidance applies the model to maintenance: illegible manuals and poorly designed checklists on the software side; inadequate tools and designs that are hard to maintain on the hardware side; cramped hangar space, noise and variable temperature on the environment side; manpower shortages and lack of supervision on the liveware side. ICAO published the 4th edition of the manual in 2018; the SHEL details in this article are taken from the 2009 edition.
What does Part-145 require for human factors training?
In EASA's continuing airworthiness rules, point 145.A.30(e) requires the organisation to establish and control the competence of its maintenance, safety management and compliance monitoring staff; that competence includes an understanding of safety management principles, including human factors and human performance. According to the acceptable means of compliance (AMC4 145.A.30(e)):
- Training is not only for technicians; it also covers managers, planners, engineers, technical records, stores and purchasing staff, and ground equipment operators.
- Initial training is completed before starting the job; new staff working under direct supervision may receive it within 6 months of joining.
- Recurrent training is delivered with an appropriate duration in each two-year period, linked to audit findings and other internal and external information.
- Training may be delivered by the organisation itself, independent trainers or training organisations acceptable to the competent authority; the procedures are set out in the maintenance organisation exposition.
The syllabus (GM1 145.A.30(e)) runs from safety risk management and human error to human performance, shift handover, error-capturing methods for critical maintenance tasks and the organisation's safety reporting scheme. SHGM's SHT-145, published on 9 February 2023 and amended on 11 January 2024, sets out the same staff list and the same "every two years" recurrent training rule in Turkish. This section is general information, not a legal interpretation; SHGM's current texts prevail.
Where should an organisation start a human factors programme?
The sequence below is not a standard but a practical starting point:
- Map the scope: use the AMC4 list to identify who needs training, without limiting it to technical staff.
- Classify occurrences in a shared language: tagging internal reports with Dirty Dozen headings makes recurring patterns visible.
- Review one task with SHELL: take a task card with frequent errors and check its procedure, tool, environment and team interfaces.
- Feed recurrent training from the floor: EASA guidance expects recurrent training to take into account information from the internal safety reporting scheme; repeating the same slides every two years does not meet that aim.
Conclusion: is human factors a training course or a way of working?
Under Part-145, human factors starts as a training requirement, but its real value shows in daily work: how shift handovers are done, how checklists are designed, how easy it is for a technician to say "I'm not sure." The Dirty Dozen is a good way to name the precursors of error, and SHELL helps link them to interfaces in the system. A practical first step is to reread the last two years of occurrence reports through these two lenses and build recurrent training around what emerges. For the risk side of safety management, see the article on hazard analysis and the risk matrix.
Human factors in aviation is part of Orient Global's corporate training catalogue; details are on the trainings page.
This article is for general information only and is not legal advice; current EASA and SHGM texts prevail.
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