While hush kits effectively reduce noise emissions from older aircraft, noise cannot always be reduced to the level of modern planes at a reasonable cost. In 1999, this concern led to a regulatory dispute between the United States and the European Union, where the EU proposed a new noise ordinance which effectively prevented the use of hush kits in Europe. This regulation threatened to reduce the value of the mostly-American used airplanes that employed hush kits and hurt the profits of American hush kit manufacturers. EU Regulation 925/99 was passed over US threats to ban Concorde but was superseded (and effectively repealed) by EU Directive No. 2002/30/EC issued March 26, 2002. In 2013, the FAA modified 14 CFR part 91 rules to prohibit the operation of jets weighing 75,000 pounds or less that are not stage 3 noise compliant after December 31, 2015. Any Stage 2 Business jets that have not been modified by installing Stage 3 noise compliant engines or have not had Stage 3 hush kits installed for non-compliant engines will not be permitted to fly in the contiguous 48 states after December 31, 2015. "14 CFR §91.883 Special flight authorizations for jet airplanes weighing 75,000 pounds or less" – lists special flight authorizations that may be granted for operation after December 31, 2015.