Originally Posted by WannEDbe
Under whose approval or regulations? Manufacturers?
Intermix must be approved under the airworthiness certification of the airplane. The beginning of the chain of approval is usually the manufacturer, who applies for it under the Type Certificate, and covers it in the Airplane Flight Manual, which is 'attached' to the airworthiness certificate of the individual airplane. The applicable regulations are, in principle, those of the state of registry of the airplane, whose authority issues the CofA. In practice, in most cases the state of registry accepts the regulation applicable in the state of manufacture as being equivalent to its own.
regards,
HN39