how acceptable quality level aql works
goods in a sample are tested at random and if the number of defective items is below the predetermined amount that product is said to meet the acceptable quality level aql if the acceptable quality level aql is not reached for a particular sampling of goods manufacturers will review the various parameters in the production process to determine the areas causing the defects the aql of a product can vary from industry to industry medical products for example have stringent aqls because defective products are a health risk as an example consider an aql of 1 on a production run this percentage means that no more than 1 of the batch can be defective if a production run is composed of 1 000 products only 10 products can be defective if 11 products are defective the entire batch is scrapped this figure of 11 or more defective products is known as the rejectable quality level rql the aql is an important statistic for companies seeking a six sigma level of quality control which is a quality control methodology developed in 1986 by motorola inc aql is also known as the acceptable quality limit industry differences in aql standardsthe aql of a product can vary from industry to industry for example medical products are more likely to have more stringent aql because defective products can result in health risks in contrast a product with benign side effects from a possible defect may have a less strict aql such as the remote control for a tv companies have to weigh the added cost associated with stringent testing and potentially higher spoilage due to a lower defect acceptance with the potential cost of a product recall customers would of course prefer zero defect products or services the ideal acceptable quality level however sellers and customers usually try to arrive at and set acceptable quality limits based on factors typically related to business financial and safety concerns using aql tablesaql tables also sometimes called aql charts are designed to allow users to reference a standard for what qualifies as an acceptable number of defects in manufacturing they allow a person to see how many defects would be allowed for a company to achieve a certain aql the tables are part of iso 2859 so for example let s say a company orders 30 000 hats from a clothing manufacturer that will be produced in one batch and the buyer and producer have agreed on aql 0 0 for critical defects aql 3 0 for major defects and aql 5 0 for minor defects referencing the aql tables would allow the buyer and producer to determine how many hats would need to be inspected to ensure that the agreed upon aql is being met during production instances of failure to meet customer quality requirements are termed as defects in practice there are three categories of defects acceptable quality level aql aql is typically considered to be the worst quality level that is still considered satisfactory it is the maximum percent defective that can be considered satisfactory the probability of accepting an aql lot should be high a probability of 0 95 translates to a risk of 0 05 rejectable quality level rql this is considered an unsatisfactory quality level and is sometimes known as lot tolerance percent defective ltpd the consumer s risk has been standardized in some tables as 0 1 the probability of accepting an rql lot is low indifference quality level iql this quality level is somewhere between aql and rql different companies maintain different interpretations of each defect type however buyers and sellers agree on an aql standard that is appropriate to the level of risk each party assumes these standards are used as a reference during a pre shipment inspection 