Butler National subsidiary Avcon Industries has added the Learjet 20 series with the XR wing modification to its hushkit supplemental type certificate (STC), and now all models of the Learjet 24 and 25 can meet the Dec. 31, 2015 Stage 3 noise limits. The modification does not restrict maximum operating altitudes of all of the Learjet 24/25 models, which includes the straight wing, Mark II, XR and Century III, according to Avcon.

“The Learjet 20 series were one of the first business jets,” said Avcon CEO Clark Stewart. “The mandate to comply with Stage 3 noise restrictions would have effectively grounded the entire fleet. Avcon has a cost-effective STC-approved Stage 3 noise compliance solution. We are committed to the long-term support of these Learjet 20 series 'workhorse aircraft.’ Our goal is to supply cost-effective solutions to these owners who would like to continue to fly their Learjet airplanes.” More than 700 Learjet 20 series were manufactured, and many are still flying.

In addition to the hushkits, Avcon also offers a Waas and ADS-B OUT STC using Garmin avionics.