A B777 flight crew on an international leg reported deviating from assigned altitude because of turb...

Attributes
ACN	891520
Time
Date	201006
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZZ.ARTCC
State Reference	FO
Aircraft 1
Make Model Name	B777-200
Operating Under FAR Part	Part 121
Person 1
Function	Pilot Flying Relief Pilot
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 165 Flight Crew Total 17885 Flight Crew Type 9555
Person 2
Function	Pilot Not Flying Relief Pilot
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 240 Flight Crew Total 12000 Flight Crew Type 7000
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Inflight Event / Encounter Weather / Turbulence

Narrative:

We were at FL388 or 11600 meters when we entered an area of light chop. We turned on the seatbelt sign; shortly after it went to moderate turbulence and we sat the flight attendant's. Nothing was painting on the weather radar and no towering cumulus were visible. Speed began fluctuating. Speed loss then became excessive and I began a descent turning off the autopilot and the other relief officer requested an emergency descent clearance from control due to moderate heavy turbulence; but didn't feel it was severe. Control cleared us to 9800 meters. In the descent we had a momentary stick shaker. We then regained speed in the descent with a nose down attitude but the aircraft began climbing in an updraft. We requested and received clearance to climb to 11600 meters. When reaching the altitude we had exited the area of turbulence and were leveled off by [our next reporting point]. Then we reengaged the autopilot and checked with the flight attendants and passengers. There were no injuries to either. The captain and flying first officer were on break at the time. The captain did a check around the airplane and reported two carts had tipped over in the aft galley but again no injuries had occurred. We then notified dispatch of the area of turbulence.

Original NASA ASRS Text

Title: A B777 flight crew on an international leg reported deviating from assigned altitude because of turbulence and performance issues.

Narrative: We were at FL388 or 11600 meters when we entered an area of light chop. We turned on the seatbelt sign; shortly after it went to moderate turbulence and we sat the Flight Attendant's. Nothing was painting on the weather radar and no towering cumulus were visible. Speed began fluctuating. Speed loss then became excessive and I began a descent turning off the autopilot and the other Relief Officer requested an emergency descent clearance from Control due to moderate heavy turbulence; but didn't feel it was severe. Control cleared us to 9800 meters. In the descent we had a momentary stick shaker. We then regained speed in the descent with a nose down attitude but the aircraft began climbing in an updraft. We requested and received clearance to climb to 11600 meters. When reaching the altitude we had exited the area of turbulence and were leveled off by [our next reporting point]. Then we reengaged the autopilot and checked with the Flight Attendants and passengers. There were no injuries to either. The Captain and flying First Officer were on break at the time. The Captain did a check around the airplane and reported two carts had tipped over in the aft galley but again no injuries had occurred. We then notified Dispatch of the area of turbulence.

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.