No fault found

No fault found (NFF), no trouble found (NTF) or no defect found (NDF) are terms used in the field of maintenance, where a unit is removed from service following a complaint of a perceived fault by operators or an alarm from its BIT (built-in test) equipment.

The unit is then checked, but no anomaly is detected by the maintainer.

Alternative descriptors include:[4] As the figure shows once a fault has been reported, investigated, and no fault found any future problems caused by the fault cause additional work which is a waste of maintainer time.

The fact remains that no fault found causes a cost to industry.

NFF is thought to cost the United States Department of Defense in excess of US$2 billion per year.