When people talk about human factors in aviation, the image is the cockpit. But a significant share of accidents begin in the hangar, days or weeks before the flight, in a task that was interrupted, in a part installed with the wrong instruction, or in an inspection that the next shift assumed the previous one had done.
The numbers are old and, for that very reason, uncomfortable. The CAP 716 publication from the British authority (UK CAA), which guides the application of human factors requirements in certified maintenance organizations, brings together the reference studies. In an analysis of 93 major accidents between 1959 and 1983 (Sears, 1986), maintenance and inspection deficiencies were a factor in 12% of them, the fourth leading cause on the list. A Boeing study of 232 commercial jet accidents between 1982 and 1991 identified a maintenance or inspection action as one of the prevention strategies in 20% of cases. And the same document records the observation that, as design, pilot training and air traffic control improve, the fraction of accidents attributable to maintenance tends to rise, not fall.
The Dirty Dozen
In the early 1990s, after a sequence of maintenance-related accidents and incidents, Transport Canada consolidated, through the work of Gordon Dupont (1993), a list of the twelve most common precursors of human error in aircraft maintenance. The list became known as the Dirty Dozen and is now adopted by the FAA as the standard vocabulary on the subject. The twelve, in the order the FAA publishes them:
- Lack of communication. The information that did not pass from one mechanic to another, from one shift to the next, from the shop to the operator.
- Complacency. The task done so many times that it stops being looked at.
- Lack of knowledge. The procedure that changed and the shop did not know.
- Distraction. The interruption in the middle of the task, which is resumed from the wrong point.
- Lack of teamwork. Each person looking after their own piece, with no one looking after the whole.
- Fatigue. The third shift in a row, the overtime to release the aircraft.
- Lack of resources. The improvised tool, the "equivalent" part, the poor lighting.
- Pressure. The customer waiting, the aircraft sold, the flight scheduled.
- Lack of assertiveness. The mechanic who saw and did not say, because the inspector had already signed.
- Stress. Personal and professional, inside and outside the shop.
- Lack of situational awareness. Not noticing what the task affects beyond itself.
- Norms. The "we've always done it this way", even when the manual says otherwise.
Thirty years later, the list has not needed revision. Not because the shop has not learned, but because the precursors are human, not technical. Technology changes; the interruption in the middle of the task keeps producing the same error.
What RBAC 145 requires, and what it does not say
RBAC 145, in Amendment 08, addresses the subject in two ways.
The first is the training program in section 145.163: every certified maintenance organization must have an initial and recurrent training program, approved by ANAC, that ensures each person assigned to maintenance, inspection and recordkeeping is able to perform the assigned tasks. Individual training must be documented and the records kept for at least five years after the end of the employment relationship.
The second is the SMS (SGSO), required by section 145.214: implementing and maintaining a safety management system appropriate to the size and complexity of the shop, with safety policy and objectives, responsibilities defined at all levels and an emergency response plan.
What RBAC 145 does not do is use the expression "human factors". It does not appear in the text. The regulation requires the shop to train and to have an SMS, and leaves it to the shop to decide how human error enters these two programs. This is a difference from the European model, in which Part-145 names the subject explicitly and CAP 716 exists to guide it. In Brazilian practice, this means that a shop that does not put the Dirty Dozen into its recurrent training and its hazard reports is formally compliant and exposed to the same old error.
Where the error happens, and where it is caught
Anyone who investigates maintenance error finds the twelve precursors in a few predictable places:
- At shift handover. A task started by one person and finished by another is the classic scenario of lack of communication. What was done, what remains, what was found out of the ordinary: if this lives in the memory of the person who left, the probability of error is high.
- At the interruption. The mechanic called to another aircraft in the middle of an installation. On returning, they resume from where they think they stopped. The defense against this is not attention: it is a record of each step, at the moment it happens.
- At the part. The right part number with the wrong serial number, the removed part that goes back on the shelf without a tag, the batch that cannot be traced. Lack of resources and norms meet here.
- At the inspection. When the inspector signs what they did not see because they trust whoever did the work. Complacency and lack of assertiveness, together.
- At the pressure. The aircraft that has to leave today. None of the other eleven precursors is as efficient at switching off the defenses.
The response of a mature shop to these points is not a poster with the list. It is a system in which every service, every part and every signature are recorded by whoever did them and at the time they were done, so that interruption, shift change and pressure do not erase what has already happened. And it is a reporting channel in which the mechanic who saw something wrong can say so, without having to confront whoever already signed.
Where Alis comes in
In Alis, the shop's work order is built precisely to support these points. Each service has who performed it and who inspected it, with an identified and dated signature. Each part applied is entered with P/N and S/N and is linked to the work order and the aircraft, with the corresponding tag in the logbook. What was found out of the ordinary becomes a recorded discrepancy, not a bulk note. And the aircraft's maintenance tracking is updated by the shop itself, at closing, which eliminates later transcription, one of the most common sources of communication error between shop and operator.
For the shop's SMS, the safety reports module accepts identified or anonymous reports, with a photo, straight from the device in the hangar, and takes the report to the risk matrix and to action follow-up. The shop's compliance with the RBAC 145 SMS is visible in the same place.
To go further on work order traceability, the article on work orders in the aircraft maintenance shop shows the path of the part from receiving to the logbook; and the one on parts and purchasing forecasting addresses the "lack of resources" precursor from the inventory side.
Want to see the work order with signature, parts and tags in the same flow? Book a demo.
This article is for informational purposes. The statistics cited are those compiled in CAP 716 of the UK Civil Aviation Authority (Appendix D: Sears, 1986; Boeing, 1982–1991) and the "Dirty Dozen" list is the one published by the FAA in its maintenance human factors program. The RBAC 145 requirements are those of Amendment 08, read on the publication date. The text does not replace consulting the regulation or the guidance of the shop's technical manager.