What does “No Defects Found” mean?

A useful thing to review on some regular basis is the number of repair requests in your maintenance system that is being closed out as “No Defects Found”. While the number of NDFs might be low in some situations, other cases may run as high as 25% or 30% of all repair requests.

If your NDF rate is 25% or 30% you probably have gotten used to spending at least some portion of every week reviewing them. In that situation, you have probably already asked yourself: “What does that level of NDF’s really mean?”

An individual NDF can mean any of the following:

1. The craft performing the repair didn’t look at the right thing. The problem was misdiagnosed.
2. The operator reported a problem that did not exist. The motivation for doing this is unclear.
3. The problem corrected itself spontaneously. This is possible with computer resets or loose connections.
4. The repair request was issued against the incorrect asset.
5. The NDF is the most convenient or memorable close-out code to use. The close-out system or coding is so cumbersome that people choose to use short-cuts.

In any case, each incident probably costs some income because of lost availability. Each incident also costs some amount of labor to the aborted repair attempt. Each NDF causes people to lose confidence in your system. NDFs also make people suspicious of others (e.g. The operator shut it down so they could take a break or the craft didn’t really do his job.)

At the end of the day, NDFs are a clear sign of a system that is not working correctly and is out of control in one way or another.

As a result, as much time should be spent investigating and eliminating NDFs as is a spent eliminating an identified defect.

This article has introduced the following concepts:

1. No Defects Found
2. What NDFs really mean
3. What effects NDFs can cause
4. The appropriate follow-up for NDFs

If readers would like to comment on these or other related subjects, they are invited to do so.