A line stop is exactly what it sounds like. A team member presses a button that prevents an assembly line from advancing. This typically happens for one of two main reasons.

Someone discovered a quality issue.
Someone was not finished with their work.

Other reasons might include maintenance problems, misplaced tools, or parts shortages. But in most cases, quality and exceeding the takt time are the biggest items that would show up as the largest bars on a line stop Pareto Chart.

Obviously, a stopped line means a lot of lost money. Leaders must act quickly to resolve the problem at hand and get the line up and running again as soon as possible. More importantly, though, they must identify the root cause of the problem and implement process changes to prevent recurrence of the issues.

Line stops are most pronounced in linked, mechanical assembly lines. In most cases, there is a big red button at each station that, when pushed, prevents the advance of the line. If the button is pressed on an indexed line (it moves when the takt time expires), there may be little impact if a response team can correct the problem before the scheduled shift. But if the clock hits 0:00, the red lights start flashing and the sirens start sounding. The same response happens immediately if the button is pressed on a continuously moving line.

Line stops, though, are not the first resort. As soon as a problem is identified, the andon cord should be pulled or button pressed, signaling the need for help. The response team is frequently able to ward off a full line stop. (Note that the andon may automatically trigger the line stop when the takt time expires.) In most situations, pulling the andon to get help also takes the decision to stop the line out of the frontline team member’s hands. The response team will likely include leaders and engineers who will decide whether to stop the line, work on the problem in transit, or pull the work off the line.

Despite the negative perception of line stops, they are highly beneficial. The pain that they cause makes the underlying problems difficult to ignore. In effect, line stops remove the safety net and force a resolution of a problem. For that reason, line stops should be looked at in a positive light, as they highlight an opportunity to fix something. If the line was not stopping for the problems, the issues would still have to be handled. They would likely continue indefinitely, though, adding waste to the process. In these cases, buffers and hidden factories end up being built into the process.

To support the improvement efforts, though, all line stops should be recorded so you know what is causing the disruptions. This data collection effort helps decide where to allocate your scarce continuous improvement resources.

If leaders get angry about line stops, team members will work to avoid causing them. This would work if the method was solely problem resolution. More commonly, though, if line stops are looked at punitively, team members will mask the reasons for the stop, especially if the cause is outside of their control.
NOTE
Getting angry and disrespectful to teams, even if there is a short-term result, causes long term harm. Plus, it violates rules of human decency.
Make sure a strong andon process is in place if you have a line stop process. Give teams a fighting chance to hit their production goals. People thrive on success.
Don’t tolerate repeated line stops. Figure out the root cause and stop the problem from recurring.
Line stops will happen even with very good organizations. They operate with less of a safety net so problems are more likely to impact production. On the bright side, though, they tend to have fewer issues than poor organizations.

Most frontline employees are, rightfully, nervous about stopping a line. There are stories about Toyota employees clapping for line stops because they see it as a quality problem that was discovered. Most organizations are not as enlightened.

The truth is that you may be in a tough spot if there is lip service about line stops being important, but then managers come down hard on teams when production is halted. First and foremost, protect yourself. Every situation is different, and line stops are a highly charged, extremely chaotic, emotional event. Make sure your actions fit in with the culture.

In many cases, though, managers act the way they do around line stops because they don’t know better. It is your job to train them. Be extremely proactive about tracking the problems causing your delays and come up with ideas on how to eliminate them. If you show your boss solutions, you’ll be more likely to get the resources to fix the problems.

Don’t ever, ever, ever show anger at someone for stopping a line. Even if you are mad, hide it and show respect. Your biggest nightmare will be if people get scared to stop production. That will give them an incentive to keep producing even if they know that there is a problem. They will start passing on poor quality and problems will go into hiding, making your job much harder.

Rather than blame employees, you should view every line stop as a leadership shortcoming. Teach people to recognize early on if they are falling behind, and get them signaling for help. But you should be going even further than that. With some foresight and proper structuring of Standard Work, line stops can be minimized while still collecting the precious data to make improvements.

Shifting gears to the subject of andons, when someone calls for help, get them some assistance immediately. If you don’t, they will stop calling for help.

You will need to have a response plan set up. When someone pulls an andon to call for help, who should respond first? At what point does the problem get escalated? How does the response team decide what to do if the problem looks significant?

These things don’t happen by chance—you have to drill them into your teams.

Line stops keep production teams from continuing to churn out poor products.
Line stops force leadership attention on a problem.
The root cause of the problems that cause line stops must be identified and eliminated.
Line stops should not be punishable offenses. If teams are scared to stop the line, poor quality will escape to customers.
Line stop processes go hand in hand with andon processes.

Make sure to start with the following steps when adding line stops to your toolkit.

Implement an andon process. You’ll have far too many line stops if you don’t deal with problems as soon as they are identified.
Set up a system to track line stops. Focus on the length of delays, not necessarily the number of instances.
Schedule improvement projects or just do on-the-spot kaizen to eliminate problems for good.

Line Stop