Air carrier first officer reports maneuvering around build ups during the arrival with the autopilot...

Attributes
ACN	853235
Time
Date	200909
Local Time Of Day	1201-1800
Place
Locale Reference	ATL.Airport
State Reference	GA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Flight Phase	Descent
Route In Use	STAR HERKO
Flight Plan	IFR
Component
Aircraft Component	Autopilot
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Engineer
Experience	Flight Crew Last 90 Days 150 Flight Crew Total 12000 Flight Crew Type 1800
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Track / Heading All Types

Narrative:

Aircraft descended to 11;400 when cleared to 12;000 in vicinity of rptor intersection. During very busy arrival into atl; after descent had begun; a different arrival than what had been already programmed was given. The new clearance was for herko arrival; cross herko at 12;000 . We were faced with buildups to over 20k in front of us just prior to herko and asked for a deviation to the right. While captain was busy reprogramming FMC; I disconnected a/P to smoothly deviate over and around buildups. Deviation with several turns made; then direct rptor. Hand flew to 12;000 and reengaged LNAV/VNAV but did not confirm auto pilot re-engagement. Noticed that aircraft was not turning after rptor and while I took control to turn aircraft. I did not maintain proper altitude. Captain and jumpseater both noticed and advised lack of a/P engagement. I should have received acknowledgment when I disconnected the auto pilot. Failure to do so and to not verify proper mode control annunciation caused me to deviate from assigned altitude.

Original NASA ASRS Text

Title: Air Carrier First Officer reports maneuvering around build ups during the arrival with the autopilot disengaged. LNAV/VNAV are engaged when complete but the autopilot is not; resulting in an altitude deviation.

Narrative: Aircraft descended to 11;400 when cleared to 12;000 in vicinity of RPTOR intersection. During very busy arrival into ATL; after descent had begun; a different arrival than what had been already programmed was given. The new clearance was for HERKO arrival; cross HERKO at 12;000 . We were faced with buildups to over 20k in front of us just prior to HERKO and asked for a deviation to the right. While Captain was busy reprogramming FMC; I disconnected A/P to smoothly deviate over and around buildups. Deviation with several turns made; then direct RPTOR. Hand flew to 12;000 and reengaged LNAV/VNAV but did not confirm Auto Pilot re-engagement. Noticed that aircraft was not turning after RPTOR and while I took control to turn aircraft. I did not maintain proper altitude. Captain and jumpseater both noticed and advised lack of A/P engagement. I should have received acknowledgment when I disconnected the Auto Pilot. Failure to do so and to not verify proper Mode Control annunciation caused me to deviate from assigned altitude.

Data retrieved from NASA's ASRS site as of April 2012 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.

Air carrier first officer reports maneuvering around build ups during the arrival with the autopilot disengaged. LNAV/VNAV are engaged when complete but the autopilot is not; resulting in an altitude deviation.