The iron and sulphur still behave like iron and sulphur in the mixture, but iron sulphide has different properties from both iron and sulphur. You can separate the iron from the mixture using a magnet but this does not work for iron sulphide. 1  Page.
Search for: An Airworthiness Directive (A.D.) is a directive issued when the FAA realizes that a perilous condition exists in a product (aircraft engine, airframe, appliance or propeller). They notify aircraft operators and owners of potentially unsafe conditions that need special inspections, alterations, or repairs.
Also included are the date the certificate was issued and the signature and office identification of the FAA representative. A Standard Airworthiness Certificate remains in effect if the aircraft receives the required maintenance and is properly registered in the United States.