While Quality Assurance deals with the processes and the people involved in developing products. Quality Control assesses the final product produced to see whether it is acceptable. That is, has it been produced to the standard expected or does it fall short of this and is therefore defective.
Quality Control is about assessing whether what's produced is acceptable.
Consider a baker who bakes cakes. Once the cakes have been baked they can be tasted to check whether they taste as one would expect. If they taste as expected that is they are tasty then they have passed the Quality Control.
If on the other hand they don't taste as one would expect then the cakes are defective and have failed the Quality Control.
When people talk about checking for defects and imply that this is part of Quality Assurance, they've confused Quality Assurance with Quality Control. As checking for defects is a Quality Control function.
"We need to Quality Assurance this product to see that it works as expected"
"If there are any faults with this product, they will come to light when we check it during Quality Assurance"
Both these quotes taken from the Quality Assurance section are incorrect because they should refer to Quality Control and not Quality Assurance.
Quality Assurance is about the process and the people involved in that process.
In certain industries a product has to be developed with certain regulations in mind. These regulations are geared to ensure high standards thus high quality. To reach these standards of high quality, rigorous Quality Control must be undertaken.
The commercial aviation industry is one where the regulations laid down by the Federal Air Administration (FAA) ensure that the level of Quality Control adopted by aircraft manufacturers must meet certain high standards.
It's understandable why such high standards are required by the FAA for aircraft manufacturers. The consequences of failure in an aircraft can be catastrophic, leading to likelihood of many fatalities.
The FAA regulations are designed to reduce the chances of aircraft failure and thus fatalities.
Likewise the Federal Drugs Administration (FDA) also impose very stringent regulations on the pharmaceutical industry. Pharmaceutical organisations have little choice but to adopt the FDA regulations.
Otherwise they will not be able to market their products in the USA and because the USA is the biggest market. The loss of profit from such a lucrative market simply cannot be ignored.
The level of Quality Control is proportional to the increased chances of injury or death from using a product.
When medicines are developed they have to undergo rigorous amounts of quality control which eventually leads to human trials. It can take years to bring a new medicine to the market and the costs involved easily run into many millions.
Like the FDA, the FAA also has to consider the increased chance of injury and fatalities when it comes to aircraft. As such the stringent mandatory imposition of strict FAA quality controls.
Both these regulatory authorities, the FAA and the FDA, do pose additional bureaucracy in the development of aviation and pharmaceutical products respectively.
However these regulations ensure that aviation and pharmaceutical products have undergone stringent levels of research, development and quality control. Leading to high quality medicines and airplanes which are safe to use.
The FDA and FAA regulations ultimately reduce important costs. Not the costs such as the development cost of a plane or a medicine but costs such as below which can be avoided by meeting regulatory demands:
Regulatory legal costs of a product failure, which include heavy fines.
Compensation costs from injuries and fatalities arising from using products that fail.
Loss of revenue due to bad publicity surrounding the failure of products.
Loss of license to trade in important markets.