A first officer reported repeated examples of excessively aggressive initial VNAV/autoflight pitch/r...

Narrative:

While level at 12;000 MSL we were cleared to descend via the marnr RNAV STAR to sea. I deleted the back calculated crossing altitude at marnr during the briefing of the arrival and its crossing altitudes. When we captured vpath at rayni we reset the altitude alerter to 6;000. With the VNAV page I reviewed the [expected] descent rates. The initial descent rate from rayni to grynd was 2;200 with all other descent rates approximately 1;800 FPM. After crossing rayni the aircraft pitched rapidly to -3;500 FPM; then to -100 FPM; then finally settled out at about 1;700 FPM descent. The remainder of the arrival was steady. I've observed this same series of events during the hawkz arrival...although not as dramatic...once as pilot flying and we reached -4;200 FPM initial descent landing north at seattle. The vpath undershoots by approximately two times the required descent rate and takes a few minutes to settle on a final descent rate. There is a real good possibility that a flight attendant or a passenger may be hurt because of the excessive deviation in descent rates before the vpath settles on a descent rate.possible problem with the vpath/autopilot/FMS interface with the new arrivals. This problem does not occur on rnp approaches. I've only observed this on these two arrivals.

Original NASA ASRS Text

Title: A First Officer reported repeated examples of excessively aggressive initial VNAV/AUTOFLIGHT pitch/rate of descent changes associated with the MARNR and HAWKZ RNAV STARs to SEA.

Narrative: While level at 12;000 MSL we were cleared to descend via the MARNR RNAV STAR to SEA. I deleted the back calculated crossing altitude at MARNR during the briefing of the arrival and its crossing altitudes. When we captured VPATH at RAYNI we reset the altitude alerter to 6;000. With the VNAV page I reviewed the [expected] descent rates. The initial descent rate from RAYNI to GRYND was 2;200 with all other descent rates approximately 1;800 FPM. After crossing RAYNI the aircraft pitched rapidly to -3;500 FPM; then to -100 FPM; then finally settled out at about 1;700 FPM descent. The remainder of the arrival was steady. I've observed this same series of events during the HAWKZ arrival...although not as dramatic...once as pilot flying and we reached -4;200 FPM initial descent landing north at Seattle. The VPATH undershoots by approximately two times the required descent rate and takes a few minutes to settle on a final descent rate. There is a real good possibility that a Flight Attendant or a passenger may be hurt because of the excessive deviation in descent rates before the VPATH settles on a descent rate.Possible problem with the VPATH/autopilot/FMS interface with the new arrivals. This problem does not occur on RNP approaches. I've only observed this on these two arrivals.

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	1081633
Time
Date	201304
Local Time Of Day	0001-0600
Place
Locale Reference	SEA.Airport
State Reference	WA
Aircraft 1
Make Model Name	Medium Transport High Wing 2 Turboprop Eng
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR MARNR THREE
Flight Plan	IFR
Component
Aircraft Component	Autoflight System
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe

A first officer reported repeated examples of excessively aggressive initial VNAV/autoflight pitch/rate of descent changes associated with the marnr and hawkz RNAV stars to sea.