An air carrier captain expressed his displeasure with the uns FMS in his aircraft that predictably e...

Narrative:

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 altitude and altitude 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.

Original NASA ASRS Text

Title: 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.

Narrative: 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.

Data retrieved from NASA's ASRS site as of July 2013 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	1006708
Time
Date	201204
Place
Locale Reference	BLI.Airport
State Reference	WA
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

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.