Comparison
SOP vs Work Instruction vs Manual
The Short Answer
Three Questions, Three Documents
Ask what the reader needs to know. If it is who does what and in what order across a process, that is a standard operating procedure (SOP). If it is how one person performs one task, that is a work instruction. If it is how a product works or how to operate or maintain it, that is a technical manual.
The first two belong to your organization. The third belongs to the product. That difference in ownership, more than length or format, is what keeps them apart.
The Hierarchy
Policy, Procedure, Instruction, Record
- Policy: why and what we commit to
- A short statement of intent and responsibility. It answers why the organization controls something and who is accountable. It rarely says how.
- Procedure or SOP: who does what, in what order
- A standard operating procedure describes a process that crosses roles or steps: receiving, inspecting, approving a change, handling a nonconformance. It answers who, when, and which records result. It is owned by the process owner and written for the people who run the process.
- Work instruction: how one task is done
- A work instruction covers a single task or station at the level of the hands: the steps, the tools, the settings, the acceptance check. It answers how, in enough detail that a trained person gets the same result each time. It is usually owned by the area that does the task.
- Form or record: what was done
- The blank form is a controlled document; the filled-in form is a record. It answers what actually happened, on which item, by whom, and when. Records are kept, not revised.
This four-level pattern is common quality-system practice, not a requirement of any one standard. The words are used loosely: one company's SOP is another's procedure, and some call a work instruction a job aid or a standard work sheet. Use the terms your own document-control procedure defines.
Side by Side
Where the Manual Sits
- SOP
- Describes your process. Owner: the process owner inside your organization. Changes when your process changes. Audience: your own staff and auditors.
- Work instruction
- Describes one task on your shop floor or in your office. Owner: the area that performs it. Changes when tooling, layout, or method changes. Audience: the person doing the task.
- Product technical manual
- Describes the product, and how anyone, including your customers, operates or maintains it. Owner: the product manufacturer or the program that sponsors the data. Changes when the product, its configuration, or its approved procedures change. Audience: users and maintainers who may never see your quality system.
A product technical manual is not a level in your hierarchy; it is something the hierarchy refers to. Your SOP for maintenance, for example, says who may perform and release the work, and your work instruction or task card says how a given job is carried out on your floor. The technical content, the limits and the approved steps, comes from the manual. For what that manual is, see what a technical manual is.
A Regulated Example
Part 145 Repair Stations
14 CFR 145.207 requires a repair station to prepare and follow a repair station manual acceptable to the FAA and to keep it current. Section 145.211 requires a quality control system and a quality control manual that describes the procedures for inspection, calibration, technical data, and corrective action, and that includes sample forms with instructions for completing them, or a reference to a separate forms manual.
In the terms above, those are the organization's procedures and forms, written down and followed. The maintenance data they depend on is the manufacturer's manual. The requirement that the station keep that data current is covered in repair station manual vs quality control manual, and the shop-level instruction that carries a job from the manual to the person doing it is covered in what an aircraft task card is.
Linking Them
How the Documents Refer to Each Other
Most problems with a document set come from duplication, not from missing pages. Five habits keep the levels apart:
- Name the question the document answers (who, how, what happened, or how the product works). If a draft answers two of them, split it.
- Give each document one owner and one revision history. A document with three owners has none.
- Make the upper level point down by title or number, and the lower level point up. A work instruction should say which procedure it supports.
- Keep product facts in one place. If a torque value or a limit lives in the manual, the work instruction should cite it, not copy it.
- Decide where the filled-in record is kept and who may correct it, before the first record is made.
Shared reference material, such as torque tables or general shop practices, has its own home. In aviation that is the standard practices manual. For revision control of the manual a procedure cites, see revision control for aviation manuals.
Writing Them
When You Are the One Writing
The writing habits carry across all three: one action per step, the order the work is done, the warning before the step it applies to, and one term for one thing. Our guides to how to write a technical manual and to the technical writing standards that apply cover the method and the standards. What changes between the three is the reader, the owner, and the consequence of an error: a bad work instruction affects one shop; a bad product manual affects every customer who follows it.
FAQ
Questions We Hear
What is the difference between an SOP and a work instruction?
Scope and audience. An SOP describes a process and the roles in it. A work instruction describes how one person performs one task. There is no single standard definition of either term, so check how your own document-control procedure uses them before you write to a template.
Is a technical manual just a very large work instruction?
No. A work instruction belongs to your organization's way of working, and an auditor reads it against your process. A product technical manual belongs to the product: it is written for whoever operates or maintains that product, and it may be a deliverable under a contract or a rule. It can be cited by an SOP or a work instruction, but it does not take its authority from them.
Can an SOP point to a manufacturer manual instead of repeating it?
Yes, and it usually should. Cite the manual by title and revision, or by the rule that says which revision applies, and keep the procedure about your own controls. Repeating manual content in an SOP creates a second copy that can fall out of date.
Where do regulated organizations draw the line?
It depends on the rule. As one example, 14 CFR 145.207 requires a repair station to prepare and follow a repair station manual acceptable to the FAA, and 145.211(c) requires a quality control manual that describes inspection and control procedures and includes sample forms or a reference to a separate forms manual. Those are the organization's own documents. The maintenance data they point to is the manufacturer's. Read the text of the rule that applies to you.
Does ISO 9001 or AS9100 require SOPs and work instructions?
Read the current text of the standard you are certified to. Quality-system standards generally ask an organization to control the documented information it decides it needs, and they leave the names and number of documents to the organization. Which documents your auditor expects to see is a question for your certification body.
Where does a task card fit?
A task card is a work instruction at the shop level: one task, with the steps, the references, and sign-off lines. It typically points up to the maintenance manual for the technical content. Our explainer on aircraft task cards covers how.
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Product Documentation That Fits Your Document Set
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