B777 flight crew experienced severe turbulence over the north atlantic at FL290. When ATC cannot iss...

Narrative:

I was the relief pilot and had just come off first break and assumed the duties of pilot flying. Random route over the atlantic. One PIREP and SIGMET from center for moderate to severe turbulence along our route. Prior shift had tried to alter course and altitude and ATC was unable to accommodate. Approaching area of possible turbulence; we briefed the flight attendants to secure the cabin and turned on the fasten seatbelt sign with an especially strong announcement to stay seated. Seatbelt sign had been on for some 10 minutes prior to encountering any turbulence at all. Encountered moderate and then severe turbulence. Made the decision to declare an emergency and followed SOP for an emergency descent to FL280 as that had been reported smooth. FL280 was much better so we stayed at that altitude until we could coordinate with ATC for subsequent climb and continue to destination. No injuries reported. Captain (who was on break) did an excellent job of briefing and establishing a game plan for possible turbulence. His obvious confidence in his crew made it easy to make a timely decision.

Original NASA ASRS Text

Title: B777 flight crew experienced severe turbulence over the North Atlantic at FL290. When ATC cannot issue a descent clearance in a timely manor; the crew exercised emergency authority and descended to FL280.

Narrative: I was the Relief Pilot and had just come off first break and assumed the duties of pilot flying. Random route over the Atlantic. One PIREP and SIGMET from Center for moderate to severe turbulence along our route. Prior shift had tried to alter course and altitude and ATC was unable to accommodate. Approaching area of possible turbulence; we briefed the flight attendants to secure the cabin and turned on the fasten seatbelt sign with an especially strong announcement to stay seated. Seatbelt sign had been on for some 10 minutes prior to encountering any turbulence at all. Encountered moderate and then severe turbulence. Made the decision to declare an Emergency and followed SOP for an emergency descent to FL280 as that had been reported smooth. FL280 was much better so we stayed at that altitude until we could coordinate with ATC for subsequent climb and continue to destination. No injuries reported. Captain (who was on break) did an excellent job of briefing and establishing a game plan for possible turbulence. His obvious confidence in his crew made it easy to make a timely decision.

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.

Attributes
ACN	871900
Time
Date	201002
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
Flight Phase	Cruise
Person 1
Function	Relief Pilot Pilot Flying
Experience	Flight Crew Last 90 Days 250 Flight Crew Total 15000 Flight Crew Type 3500
Person 2
Function	First Officer Pilot Not Flying
Experience	Flight Crew Last 90 Days 80 Flight Crew Total 15000 Flight Crew Type 8000
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Inflight Event / Encounter Weather / Turbulence

B777 flight crew experienced severe turbulence over the north atlantic at FL290. When ATC cannot issue a descent clearance in a timely manor; the crew exercised emergency authority and descended to FL280.