No Fault Found

Reducing the “No Defect Found” Problem with Expert Systems
A sure sign that a problem is important is when it has many different names. No Fault Found (NFF), No Defect Found (NDF), No Problem Found (NPF), Retest-OK (RETOK) or Could Not Duplicate (CND) — whatever you want to call it, “ghost” failures make fixing healthcare technology systems a chore.

W hen service personnel need to resolve equipment problems, they often “board-swap”, removing Field-Replaceable Units (FRUs) from the malfunctioning medical equipment and replacing them with spare parts. The removed FRUs are often returned to a depot for repair. If depot-level testing can’t discover any FRU functional failure, it renders a verdict of NFF, NDF, NPF or CND — depending on their organization’s type and regulations — and returns the FRU to the spares pool.

A 1995 Reliability Society “failure rate prediction survey” determined that NDF was a major finding in about half of all FRUs returned to the depot. It raises the required levels of spare parts inventories, increases pipeline time and adds to the cost of depot work and manpower.

Another safety-critical industry, airline transportation, may have some lessons for healthcare service managers seeking to improve field service efficiency. A USAirways study showed that the NFF problem has strong impact on Mean Time Between Unscheduled Removal (MTBUR) and Mean Time between Failures (MTBF). The Air Transport Association determined that 4,500 NFF “events” cost its member airlines $100 million annually, as well as causing thousands of flight delays and cancellations.

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