What Is Andon?
Also known as: andon cord, andon board
Definition
Andon is a visual and audible signaling system that lets any operator immediately alert supervisors and support staff to an abnormal condition, and in its full form authorizes stopping the line until the problem is addressed.
Andon Explained
Physically, an andon is a light stack, a pull cord or button, and usually a display board showing station status across a line. The common color convention is green for normal running, yellow for a problem that needs help but has not stopped production, and red for a stopped condition. Some plants add blue for material shortage and white for changeover. The board makes plant state legible at a glance, without a meeting or a report.
The behavioral content matters far more than the hardware. Andon works only if pulling it is expected, safe, and answered. Toyota's version pairs the signal with a fixed-position stop: the line continues to the end of the cycle while a team leader responds, and stops only if the problem is not resolved by then. That design gives the operator authority to escalate immediately while limiting the cost of a false alarm, which is what makes frequent honest signaling sustainable.
The defining failure mode is an andon nobody answers, or worse, one that gets an operator criticized for using. Within weeks operators stop pulling, the board shows uninterrupted green, and management concludes quality is excellent while defects continue to flow downstream. A useful health check is the pull rate: a line with zero andon events per shift is almost never a line without problems, it is a line where signaling has been suppressed.
Modern andon is frequently integrated rather than standalone. Signals feed an MES or downtime system, timestamped with station, reason code, and response and resolution times, which produces the raw data for Pareto analysis of stop causes and for measuring response latency as its own metric. Where that data flows into the ERP, andon events can be reconciled against job transactions to explain schedule misses with evidence instead of recollection.
Why It Matters
- Escalates problems in seconds rather than at end of shift, so containment happens before defective units flow downstream.
- Measured response time exposes whether the support structure actually supports the line, a fact usually invisible to management.
- Andon event data provides a reason-coded Pareto of stoppages, which is the raw material for targeted improvement instead of general exhortation.
- Makes plant status visible without meetings, letting supervisors direct attention to the station that needs it rather than the loudest one.
In Practice
A plant installs andon stacks and a large status board, then reports near-continuous green after two months. Audit of the line shows operators are handling problems informally because the first several pulls produced a fifteen-minute wait and a question about why the line was stopped. The corrective action was organizational, not technical: a named responder per zone, a two-minute response standard, response time posted publicly, and supervisors explicitly measured on answering signals rather than on minimizing them.
Frequently Asked Questions
Does pulling the andon stop the entire line?
Usually not immediately. In the fixed-position stop design used by Toyota, the pull summons a team leader while the line finishes the current cycle, and it stops only if the issue is unresolved when the unit reaches the end of the station. This preserves the operator's authority to escalate while keeping the cost of a false alarm low enough that people actually use it.
What are typical andon light colors?
Green indicates normal operation, yellow signals a problem requiring assistance without a stop, and red indicates a stopped condition. Many plants add blue for material or component shortage and white for a planned changeover or end of run. Colors should be standardized plant-wide, since inconsistent conventions between lines defeat the purpose of at-a-glance status.
Related Terms
Poka-Yoke
Poka-yoke is a mistake-proofing technique that designs a process or fixture so a human error either cannot occur at all or is detected immediately, before it becomes a defect passed to the next operation.
Lean Manufacturing
Lean manufacturing is a production philosophy derived from the Toyota Production System that maximizes customer value by systematically identifying and eliminating waste, defined as any activity that consumes resources without adding value the customer would pay for.
MTTR (Mean Time To Repair)
MTTR (Mean Time To Repair) is the average time required to restore a failed asset to full operating condition, calculated as total repair time divided by the number of repairs. It measures maintainability rather than reliability.
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