Garrett Aviation announced it has received STCs for RVSM avionics retrofits in Cessna Citations 501, 550 and 551, as well as later 500 models. A certification program for the 560 is under way, according to a spokesman. The RVSM compliance packages each include two air-data display units (ADDU) and an analog/digital interface unit (AIU) built by Innovative Solutions & Support of Malvern, Pa. The ADDU includes a self-sensing digital air-data-computing altimeter with integral altitude alerting, while the AIU provides the interface to autopilot and navigation systems. Complete hardware prices start at a little over $100,000, and anticipated downtime for the mod is two weeks. Cessna said RVSM modification verification flights using FAA GPS monitoring units are available for operator use. Meanwhile, Duncan Aviation announced receipt of RVSM group approval for the JetStar II.