Ltpd
Lot Tolerance Percent Defective (LTPD) is an acceptance-sampling quality level representing the worst defect rate a sampling plan is designed to reject most of the time. In standard practice, lots at the LTPD are rejected about 90% of the time, or accepted at most 10% of the time. It serves as a consumer-protection point in lot inspection.
On the receiving dock, LTPD is applied through an acceptance sampling plan tied to incoming inspection. A technician samples a palletized raw-material lot, and the plan's OC curve determines whether the defect count falls beyond the reject threshold. If the lot's quality is at or worse than the LTPD, the statistical expectation is rejection, so the lot is routed to material review, quarantine, or 100% inspection. This matters most for high-risk inbound items like castings, fasteners, electronics, and packaged consumables, where a defective lot can create line stoppages, rework, or downstream escapes. In warehousing, LTPD rules can be embedded in WMS or MES receiving logic to trigger sampling, traceability holds, or supplier scorecard actions. Paired with AQL, it balances producer and consumer risk: AQL defines acceptable quality that should usually pass, while LTPD defines rejectable quality that should usually fail. It is a lot-disposition control, not an inventory metric.
- False acceptance of a bad lot: Weak sampling plans can accept lots at or worse than the LTPD, sending defective material to the line. Failures emerge as scrap, jams, or inspection escapes because only part of the lot is checked.
- Receiving bottlenecks from over-tight sampling: Applying LTPD without balancing AQL and sample size escalates many lots to secondary inspection or quarantine. This slows dock-to-stock flow, blocks put-away, and starves production of critical components even when lots are usable.
- Misusing LTPD as a defect target: LTPD is not a process capability goal. Using it as a KPI distorts behavior because it sets lot-rejection thresholds, not SPC limits or defect-reduction targets.
What probability of acceptance corresponds to LTPD?
About 10% acceptance, or 90% rejection, for a lot at the LTPD.
What curve is used to find LTPD?
The sampling plan's operating characteristic (OC) curve.
What risk does LTPD mainly protect against?
Consumer's risk—accepting a lot that is too defective. LTPD is enforced through incoming acceptance sampling rules, lot release criteria, and quarantine or rejection decisions in quality and materials control.