ATC initiated alterations to the gibzz RNAV STAR may have contributed to an altitude deviation for a...

Attributes
ACN	1045153
Time
Date	201210
Local Time Of Day	1801-2400
Place
Locale Reference	IAD.Airport
State Reference	DC
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Descent
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	Pilot Flying First Officer
Experience	Flight Crew Last 90 Days 250 Flight Crew Total 14000 Flight Crew Type 2600
Events
Anomaly	ATC Issue All Types Aircraft Equipment Problem Critical Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy

Narrative:

Got late 'descend via' for gibbz RNAV arrival; first portion of arrival was deleted by ATC; with instructions to cross mosle at 11;000 ft. [We] had to confirm that ATC wanted us to continue to descend via the arrival after mosle and wanted published 250 KTS speed at mosle. We had been in VNAV path with gibbs altitude of 7;000 ft set when this clearance was received. We then went to flch with assigned altitude of 11;000 ft. As we approached 11;000 ft the FMA went to altitude cap mode; as expected; but the jet descended right through 11;000 ft in full autopilot with altitude cap annunciated. We deselected the autopilot and bottomed out at 10;750; then returned to 11;000. The remainder of the arrival was normal; but we conducted all further descents in flch and selected speed.

Original NASA ASRS Text

Title: ATC initiated alterations to the GIBZZ RNAV STAR may have contributed to an altitude deviation for a Boeing flight crew when the autoflight system failed to arrest their descent at 11;000 per the MCP altitude window and the active FLCH mode.

Narrative: Got late 'descend via' for GIBBZ RNAV arrival; first portion of arrival was deleted by ATC; with instructions to cross MOSLE at 11;000 FT. [We] had to confirm that ATC wanted us to continue to descend via the arrival after MOSLE and wanted published 250 KTS speed at MOSLE. We had been in VNAV PATH with GIBBS altitude of 7;000 FT set when this clearance was received. We then went to FLCH with assigned altitude of 11;000 FT. As we approached 11;000 FT the FMA went to ALT CAP mode; as expected; but the jet descended right through 11;000 FT in full autopilot with ALT CAP annunciated. We deselected the autopilot and bottomed out at 10;750; then returned to 11;000. The remainder of the arrival was normal; but we conducted all further descents in FLCH and selected speed.

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.

ATC initiated alterations to the gibzz RNAV STAR may have contributed to an altitude deviation for a boeing flight crew when the autoflight system failed to arrest their descent at 11;000 per the MCP altitude window and the active flch mode.