Commercial Fixed Wing
Flight Crew Air Transport Pilot (ATP)
Distraction; Workload; Human-Machine Interface
Aircraft Equipment Problem Less Severe
Flight Crew Overcame Equipment Problem
Aircraft; Human Factors; Procedure
When flying the BLI RNAV 34 approach VNAV disconnected when the airplane turned in at TUBTY Intersection. As I have had this happen many times before I was prepared for it and reprogrammed the FMS. This is a very high workload event and although we had no deviations I see ways a crew could do so. Possible errors would be forgetting to put in an ALT and ALT SEL and going through 2;000 MSL. Or when the airplane levels it would be easy to get slow and have a stall warning while programming the FMS. I have tried many times to program the FMS to avoid the VNAV disconnect on this approach and know of no way around the problem. The Tech Pilots are aware the problem has existed for years. Why is there no fix for the problem or why hasn't the approach been NOTAMed OTS?UNS needs to make a product that works correctly and is difficult to mis-program. I'm disappointed in our Tech pilots' inability to solve a known problem.
An air carrier Captain expressed his displeasure with the UNS FMS in his aircraft that predictably exits VNAV mode when passing TUBTY IF on the RNAV Runway 34 IAP at BLI.