Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Engineer
Flight Crew Last 90 Days 3; Flight Crew Total 17700; Flight Crew Type 240
Troubleshooting; Confusion; Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Executed Go Around / Missed Approach
Aircraft
Enroute from ZZZ to APF; we were cleared direct to UGYOW to descend to 2;100 feet; and we were cleared for the RNAV 23 approach at APF. About 4 NM from UGYOW; the FMS dropped UGYOW from our route completely; and the final approach course with a line to infinity was redrawn on our MFD with OFDOY still in view. The FMS commanded a turn to intercept the final approach course at a 45 degree angle; inside OFDOY.Here's what's so strange about this. We had the same anomaly happen to us on the same routing several months ago. I was ready for it today; but the airplane still turned and there was a minute of confusion and discussion because our next fix UGYOW was no longer in view; and dropped from the FMS. We had no guidance anymore to UGYOW. Having had this happen twice now; I have to say with confidence; there is an issue with the Universal UNS-1E FMS we have on board to provide this guidance. I realize the turns necessary to get us on the final approach course are significant in this procedure; but the FMS should not drop the IAF fix from view and redraw the final approach course as it is doing. Someone at Universal and the FAA need to look into this; and they need to publish that this procedure can't be used when coming from the SW so that others don't have this bad experience. There was no conflict with traffic; but the controller got a little excited when we first made the turn; and he canceled our approach clearance; and turned out back out to the NE and he gave us radar vectors to the final approach course; which worked out perfectly. My copilot on this flight had been an instructor on the Aircraft X at [the] simulator training center for years; and he agreed the FMS shouldn't have done that and its guidance is wrong when this happens. I will contact Universal to discuss it with them; and I plan to try this approach in the simulator when I go back for recurrent training.
Corporate pilot reported that while on an RNAV approach; the Universal UNS-1E FMA dropped the IAF and redrew the final approach course. Reporter stated this had happened previously on the same routing.