They are usually made of inferior materials by inadequate processes and not tested, designed only to bear a close resemblance to genuine parts.
[9] In 1996 unapproved parts were found to originate from sources such as counterfeiters, thieves, "strip and dip" operations which hide defects with metal plating, and from production overruns.
[8] Counterfeit bolts, attaching the vertical stabilizer of a Convair CV-580 to the fuselage, wore down excessively, allowing the tail to vibrate to the extent that it eventually broke off.
By 1996, the investigations resulted in hundreds of criminal convictions, restitution, fines totalling about US$47 million, and prison sentences of up to five years.
[8] In August 1993, a group of criminals stole a cockpit computer from a Carnival Airlines aircraft at Fort Lauderdale-Hollywood International Airport.
[11] In response, American Airlines published a 14-page list of the parts missing from the crashed aircraft, including the serial numbers.
[8] An FAA study concluded that, from May 1973 to April 1996, unapproved parts contributed to 174 aircraft accidents and minor incidents, causing 39 injuries and 17 fatalities.
[8] The United States Congress passed the Aircraft Safety Act of 2000, allowing the government to target the sale and use of unapproved parts.