There are few concepts more confusing for aerospace manufacturers than that of “Human Factors” (HF). You shouldn’t feel alone if you’re confused, as there’s a reason for this, which I will explain. Fortunately, implementing a quality system that takes HF into account is not too difficult.

First, you should understand that everyone gets confused about HF in a manufacturing environment, largely because the concept is only well defined in other environments. In FDA regulated medical or pharmaceutical industries, they have certain approaches and interpretations for HF that are well defined and documented. Ditto for aviation maintenance, repair and overhaul (MRO) shops, which follow guidance published by the FAA, ICAO or other aviation agencies. We don’t have that for manufacturing, however.

Worsening matters, the authors of the AS9100 standard shoehorned the HF concept into the standard, without fully understanding how it applies to manufacturing themselves. They appear to have borrowed the text from AS9110 — the standard for MROs — without realizing they are adding apples to oranges. Many of the HF approaches that work in repair stations are not sufficient for manufacturing, and they don’t address HF related to product or process design at all.

Furthermore, the authors of AS9100 seem to have confused Human Factors, with human error. One of the references to HF is in the context of preventing human error, and that’s fine, but it’s a woefully minuscule part of what makes up HF, and why it’s important.  Some of the IAQG’s supporting documentation on the subject repeats this sin, telegraphing to the world that their so-called experts on the standards committee really have no idea what Human Factors is. Even worse, many often confuse HF with workplace ergonomics (comfy chairs! cushioned mouse pads!), which reduces the concept to near insult.

So once again, let’s let Oxebridge do the heavy lifting, and explain it.

HF in a Manufacturing Context

Let’s start by remembering that AS9100 exists to ensure the quality of products delivered to the aerospace supply chain. It’s not about workplace safety or occupational health and safety — ISO has other standards for that. Throw out the argument about cushioned mouse pads.

HF in the manufacturing space is intended to ensure that operators and employees can produce the products with a high degree of quality and consistency, taking into account certain risks or issues that could be introduced by the very fact that we are human beings. By this I mean we are gangly, ugly lumps of skin and bones and liquids, operated by limited brains, and those physical realities have certain limitations, and create certain risks. This is what HF is attempting to mitigate, to the extent that it can.

Therefore, any HF program should ask one question: what risks to quality are created due to the physical and mental limitations created by simply being human beings? This will push you towards a set of key areas to consider, sometimes called the PEAR model (no, not the Tim Lee process audit form, thankfully.)

The PEAR model asks you to consider human limitations related to the Process, Environment, Actions and Resources. Again, this largely comes from the aviation repair station world, but can be translated into a useful application for aerospace manufacturing.

By the way, before we get into too much detail, I recommend creating a brief Human Factors Manual; this must be kept simple and short, and for very small companies, this may be merely a procedure (not a full manual.) In the document, however, you will then define your approaches to HF related to the PEAR aspects, as we will discuss. Your approaches will be different from everyone else, so this has to be customized.

Again, though: keep it simple!


When considering HF related to processes, the first thing to be considered is process design. Unfortunately, both ISO 9001 and AS9100 are largely silent on this subject, an absolute sin for any process engineer. (This is largely due to the fact that there are no process engineers on the committees that write these standards, and the entire push to add process management comes from a truncated understanding of Deming, and nothing more.)

When designing manufacturing processes, you should consider developing a set of answers to the following question:

How can the physical and mental limitations of human beings be mitigated within this process?

This may be answered by ensuring the processes are designed so that humans can physically do the work. If not, they must be corrected.

What does this mean? Well, the scope of the question is huge, and you have to dial it down to something you can actually implement. Typically, HF wants you to consider the following:

  1. What process elements can you design to ensure the operators can perform the work based on their size, body strength, physical limitations, age, etc? This may mean ensuring certain tools are developed to assist in performing the work, or lighting is implemented, ladders installed, etc. If your product is 7 feet high, then your 5-foot-9 inspector isn’t going to be able to inspect it.
  2. What can you do to ensure the work can be done considering human stress factors? Again, we are not getting into occupational health and safety (although, admittedly, we are on the border), but instead what stresses might be introduced by a poorly designed process which might impact on quality? For example, does the process require workers to run from one side of the building to another in order to get the work done, thus increasing stress? Does it require a single operator to conduct multiple steps at once, pushing the boundaries of what is actually possible? Does it rely on unrealistic schedules?
  3. What training will you need to implement in order to support the process? You have to take a realistic account of your workforce’s abilities, and then provide the training so they can execute the process. This should already be covered by your standard “competency” requirements per ISO 9001 and AS9100, but it’s good to double-back and think this through again when developing a new process.
  4. How can you design the process to reduce conflict? Again, we are not trying to implement a “feel good” workplace here, for its own sake. But HF wants you to consider if you are intentionally or accidentally creating unnecessary stress which can then risk product quality. Think of this in practical, and not theoretical, terms. For example, don’t create process steps that require a lower level employee to report problems to upper management if your company culture is likely to punish the poor sap for doing so. Be sure that shift hours don’t get so out of hand that it results in workers being overworked to the point of exhaustion, and they start fighting with each other. To keep yourself on track and prevent getting too wild here, keep coming back to the core question, “will this affect quality if we don’t address it?”
  5. What about language issues? This, frankly, can go into any of the PEAR aspects, so I threw it in here. I’m going to upset a lot of my readers, but too bad: if you hire workers who don’t speak English, then you’d damn well better have your training and instructions provided in the language they do speak. I am exhausted by companies that hire immigrant labor to save money, and then tell me “if they can’t speak English, they shouldn’t be working here,” as if it’s the worker’s fault for being hired by the company. That’s not how it works; the responsibility is on you to provide the training and instructions in their language, or you’d better have a magic machine that teaches everyone English in a half hour by plugging a wire into their brain or something. You can’t have both low-paid immigrant labor and a fully-trained workforce unless you provide procedures or training in their language. Given the super low cost of machine-driven translation (Google, DeepL, etc.), there’s really no excuse.

In a practical sense, you would develop a list of questions for your process designers to consider — such as those above — and put that in your HF manual or procedure. They would be guidance only, since every situation would be different. But it would get your process designers thinking about how to reduce error and nonconformities up front, before the process was even implemented.

From this, your process designers would then ensure there were sufficient procedures, training methods, resources and controls to address whatever answers they come up with for those questions.


Here things get a bit more simple. In a manufacturing environment, the question is merely “what aspects of the work environment could introduce defects if not addressed? It’s simply an extension of the work environment requirements already present in ISO 9001 and AS9100, and you may have already satisfied this completely. But let’s examine it anyway.

(An aside: I am yet again intentionally ignoring the ridiculous New Age “emotionally protective workplace” notes injected into AS9100 here.)

For this aspect, consider developing answers to the following questions:

  1. How can we control the physical work environment to reduce human-related defects? This may mean adding resources or workplace environmental controls related to temperature, air handling, lighting, humidity, sound levels, etc. In each case, the primary consideration is whether product would be impacted, but in some cases  you do have to consider whether humans will be harmed or distracted. For example, an overloud machine may distract workers, resulting in them screwing up their job. While we obviously don’t want people getting injured, that’s not the focus here (remember, we have other standards — and laws — for that.)  Yes, you provide hearing protection to prevent injury, but in this context  you must do so to reduce distraction.
  2. Can workers physically perform the work, given the physical restrictions of either the work environment or the product? Again, this is the “ladder” scenario, but also would apply to enclosed workspaces, cramped working conditions, etc. For example, if an assembly operation requires rotating a 3-foot long tool, do you actually have three feet of clearance, or is it going to bump into something? If the work requires climbing inside an aircraft compartment, have you provided necessary FOD protections, portable lighting, ventilation?
  3. How can we organize the work environment to reduce defects? Here you should consider the physical layout of the work areas, as well as any production schedules, work shifts, crew size, etc.

This one gets tricky because you will constantly appear to be bumping up against the “emotionally protective workplace” aspect, but you have to resist the trap. You are implementing these controls first and foremost for product quality. If that has a Venn Diagram overlap with worker happiness and tranquility, that’s great, but that’s not your focus here. You can address those things outside of your quality system (and should, unless you’re a bastard.)


This aspect is basically handled through proper implementation of procedures and/or training (usually both.) To address this, ask the following questions:

  1. How can we simplify the process to make it easier for operators to perform the work without making errors or defects? This means examining ways to reduce repetitive steps, clarifying confusing operations,
  2. Is the sequence of our operations or processes adequate? Here you want to be sure you are not creating risk or inefficiency by sloppy process layout or order of steps. Do you have people running around like headless chickens? Do you have too many steps? Not enough? Are they in the wrong order?
  3. What training can we provide to increase the ability of our operators to perform the work without defects? Again, does the work require special training? Have you developed the training, and then provided it? So many companies blame operators for errors, but then have never provided adequate training because the staff responsible for training are secretly too lazy to do it. This doesn’t work in aerospace because you’re making things that fall out of the sky. Develop training programs and implement them, period. No excuses here.
  4. What tools and resources do we need to ensure the people can physically perform the actions? Sure, this is a recurring theme, but you have to keep asking it at every turn. If a work “action” requires turning a massive valve, have you provided the proper wrench to do so, or are you expecting your 90-pound operator to do it with his scrawny little arms?
  5. Are requires actions likely to cause injury? Here we are not addressing safety or occupational health and safety (sorry to repeat myself), but consider that if you have unsafe operations and someone gets hurt, this means you better have replacement staff available or the work wont’ get done, and your product will ship late. Remember AS9100 is obsessed with on-time delivery.

In many cases, the HF considerations related to “Actions” will consist of reviewing current methods and approaches, and tweaking them. This likely won’t be a heavy lift.


The implementation of HF related to the design of aerospace product isn’t typically called out in official manuals or industry guidance documents, and the PEAR model doesn’t address it either. But it’s critical to consider, so let’s add it now.

This can get confusing, but bear with me: here we are only concerned with how to design product so that it can be manufactured, inspected and delivered later by those gangly meatbags, your humans.  You want to be careful that you are not confusing the aspects of design related to its eventual functioning; that’s covered by AS9100’s clause on product safety, and I don’t want to conflate the two issues. (You’ll eventually have to satisfy both, however, to be AS9100 compliant.)

When designing product, ask the following questions:

  1. Can the physical dimensions and tolerances be manufactured and inspected by my humans? If not, you need to go back and adjust the design, or plan on how to address the PEAR models questions later, related to those dimensions and tolerances. For example, if you put a ridiculously tight tolerance of +/- 0.0001″ on a seven foot length dimension, you had better have equipment that can measure that, because your humans cannot do so with a retractable tape measure from Wal-Mart. If the part has intricate internal curvatures, can you even get a tool in there to machine or measure it? Design engineers often forget to consider manufacturability when design product, and this question attempts to address that, from the HF perspective.
  2. Does the product design — including materials — create risks for quality? For example, if your product is to be made from magnesium, have you ensured your PEAR controls (above) will ensure operators can’t accidentally start an explosive fire? Do you have proper equipment for handling or manufacturing the product (inert atmospheres, glove boxes, etc.)?
  3. Does the product rely on outsourced processes which may introduce additional HF risks to quality? If you are over-reliant on outsourcing, you may have to develop procedures and controls to flow down to your outsource process providers, for use by their personnel. If they screw up your product, it’s still your fault in the eyes of the customer, so the burden is on you to control this.

You had ONE job.

Putting HF to Work 

As I said, I suggest putting all of this together in a single HF Manual or set of procedures that answers these questions in practical terms, tailored for your specific product realization activities. Then, of course, you have to publish the HF documents and ensure people are trained on them. Include some simple HF related questions in your internal audit checklists, to ensure ongoing compliance.

The AS9100 standard references HF in the context of corrective action, so be sure any corrective action procedure makes circular reference to your HF documents, and that Human Factors are at least considered during the root cause analysis and any subsequent action plan. You don’t need to provide detailed evidence of this on every individual corrective action request form, if you call out the need for folks to “consider HF when performing root cause analysis and developing action plans” in your procedure.

Finally, be ready to defend your HF approaches during inevitable AS9100 audits. The auditors are even less informed than the authors of the standard, so they will be trotting out the most inane leading questions on the subject, pushing you towards ergonomic lumbar supporting desk chairs, scented candles and hiring an on-call emotional support therapist. None of this is required. Instead, push your HF Manual in their face, say “this is our HF program, read it.” Then they can audit you to that, not to their imagined fantasies.

At all times, constantly remind yourself and others that HF in aerospace manufacturing is about ensuring the work can be performed by humans without introduction of defects or errors. That’s the focus.

In the meantime, if you get confused about HF in a practical sense, do a simple Google search for images related to the phrase “you had one job” (or just click here.) The results are simultaneously hilarious and informative, and will quickly get you up to speed on what HF should be addressing.


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