FlightPathOBN,
VxWorks is a operating system. It doesn't have anything to do with the language the system is written in. You can run C, C++ or Ada on top of VxWorks. VxWorks is popular but there's quite a bit using Green Hills INTEGRITY now because its DO-178B out of the box.
If you're talking about the FMS itself, Honeywell originally used Pascal, Pegasus is Ada (based on Pascal), Primus EPIC is C on a proprietary OS, and the A380 system is C++ on top of INTEGRITY.
Boeing likes Ada, 70% of the 777 is written in Ada. I confirmed the Airbus BSCU, FWC, FCDC is in Ada, and the A350 ADIRU will be Ada on INTEGRITY.