Hush kit

Most hush kits make further modifications to the exhaust, including acoustically treated tailpipes, revised inlet nacelles and guide vanes.

Modern aircraft equipped with mid and high-bypass turbofan engines are designed to comply with contemporary aviation noise abatement laws and ICAO regulations.

Several older aircraft that are still in service (typically in a cargo capacity) have hush kits retrofitted so that they are able to conform with noise regulations needed to operate in many commercial airports.

[7] 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.

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.