Nextant Aerospace 604XT Fusion Upgrade Coming In Q4 Remanufacture specialist Nextant Aerospace says that they expect to gain supplemental type certification (STC) from the Federal Aviation Administration (FAA) for the avionics Fusion upgrade to the 604XT (originally the Bombardier Challenger 604) in the fourth quarter of 2018. The Challenger 604 came with the Rockwell Collins Pro Line 4 avionics suite and is being upgraded to the Rockwell Collins Pro Line Fusion flight deck -pending certification-. This represents the first phase in the modernization of the Challenger 604 to the Nextant Aerospace 604XT. Other planned upgrades for the jet will be a wing extension and refinement that will boost the range by nearly 500 nautical miles. A new interior is also expected to be designed to meet the current high-end standards in the industry.