Home » Alloy Achieves STC for Hush Kits Alloy Achieves STC for Hush Kits May 12, 2016 Hush kit manufacturer Alloy Aerospace Inc. has been granted FAA STC approval for their Stage 3 Learjet 20 series (24,25) Hush kits. STC number ST02583LA was issued 20APR2016.