B767 captain used his emergency authority/authorized to avoid reported severe turbulence.

Attributes
ACN	460638
Time
Date	200001
Day	Fri
Local Time Of Day	1201 To 1800
Place
State Reference	NF
Altitude	msl bound lower : 29000 msl bound upper : 31000
Environment
Flight Conditions	VMC
Weather Elements	Turbulence
Light	Daylight
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B767-300 and 300 ER
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	cruise : enroute altitude change cruise : level
Route In Use	enroute : atlantic enroute other
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : multi engine pilot : instrument pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 140 flight time total : 10000 flight time type : 5000
ASRS Report	460638
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Events
Anomaly	altitude deviation : excursion from assigned altitude inflight encounter : turbulence inflight encounter : weather non adherence : clearance
Independent Detector	other flight crewa other flight crewb
Resolutory Action	flight crew : declared emergency flight crew : returned to assigned altitude
Supplementary
Problem Areas	Weather Flight Crew Human Performance
Primary Problem	Weather
Air Traffic Incident	Pilot Deviation

Narrative:

We were proceeding with an oceanic crossing at FL310, track 'echo.' I was the PF. The captain and I were in the cockpit, the other first officer was on his rest break. We began to encounter varying degrees of turbulence. Several aircraft were giving reports on turbulence. One report was from an aircraft routed along our track (east) at FL330. He preceded us by approximately 4-6 degrees of longitude. He reported encountering 'severe turbulence' and some degree of 'loss of control.' our turbulence increased to 'moderate turbulence,' and if there could be different levels of 'moderate,' I would call it 'heavy' moderate. During this time (beginning when we first experienced some turbulence) the captain and I discussed our options concerning cabin notification, aircraft speed, engine ignition and possible avoidance actions. Based on our current turbulence level, WX reports, PIREPS, etc, the captain wanted to descend. I expressed my disagreement with that action. Passing 38 degrees west longitude the captain assumed control of the aircraft, and with increasing concern for the possible severe turbulence in front of us, began a descent. I again expressed my disagreement with the decision to descend, and wanted to offset our route if we continued. He noted my objections and continued down along the route. At this point I contacted gander radio to get a clearance for FL290. We had reached FL290, the ride was smoother (light chop only) and I expressed my desire to climb back to our filed and cleared altitude. Gander radio responded to our request, but was unable to approve FL290, and the captain began a climb back to FL310. We were level again at FL310 just passing 39 degrees west longitude. The turbulence we encountered earlier was not present and the remainder of the flight was uneventful. Shortly thereafter I was relieved by the other first officer and began my rest break which lasted until approximately 35 mins before landing. There was little discussion of the event, but I informed the captain of my intention to file this report.

Original NASA ASRS Text

Title: B767 CAPT USED HIS EMER AUTH TO AVOID RPTED SEVERE TURB.

Narrative: WE WERE PROCEEDING WITH AN OCEANIC XING AT FL310, TRACK 'ECHO.' I WAS THE PF. THE CAPT AND I WERE IN THE COCKPIT, THE OTHER FO WAS ON HIS REST BREAK. WE BEGAN TO ENCOUNTER VARYING DEGREES OF TURB. SEVERAL ACFT WERE GIVING RPTS ON TURB. ONE RPT WAS FROM AN ACFT ROUTED ALONG OUR TRACK (E) AT FL330. HE PRECEDED US BY APPROX 4-6 DEGS OF LONGITUDE. HE RPTED ENCOUNTERING 'SEVERE TURB' AND SOME DEGREE OF 'LOSS OF CTL.' OUR TURB INCREASED TO 'MODERATE TURB,' AND IF THERE COULD BE DIFFERENT LEVELS OF 'MODERATE,' I WOULD CALL IT 'HVY' MODERATE. DURING THIS TIME (BEGINNING WHEN WE FIRST EXPERIENCED SOME TURB) THE CAPT AND I DISCUSSED OUR OPTIONS CONCERNING CABIN NOTIFICATION, ACFT SPD, ENG IGNITION AND POSSIBLE AVOIDANCE ACTIONS. BASED ON OUR CURRENT TURB LEVEL, WX RPTS, PIREPS, ETC, THE CAPT WANTED TO DSND. I EXPRESSED MY DISAGREEMENT WITH THAT ACTION. PASSING 38 DEGS W LONGITUDE THE CAPT ASSUMED CTL OF THE ACFT, AND WITH INCREASING CONCERN FOR THE POSSIBLE SEVERE TURB IN FRONT OF US, BEGAN A DSCNT. I AGAIN EXPRESSED MY DISAGREEMENT WITH THE DECISION TO DSND, AND WANTED TO OFFSET OUR RTE IF WE CONTINUED. HE NOTED MY OBJECTIONS AND CONTINUED DOWN ALONG THE RTE. AT THIS POINT I CONTACTED GANDER RADIO TO GET A CLRNC FOR FL290. WE HAD REACHED FL290, THE RIDE WAS SMOOTHER (LIGHT CHOP ONLY) AND I EXPRESSED MY DESIRE TO CLB BACK TO OUR FILED AND CLRED ALT. GANDER RADIO RESPONDED TO OUR REQUEST, BUT WAS UNABLE TO APPROVE FL290, AND THE CAPT BEGAN A CLB BACK TO FL310. WE WERE LEVEL AGAIN AT FL310 JUST PASSING 39 DEGS W LONGITUDE. THE TURB WE ENCOUNTERED EARLIER WAS NOT PRESENT AND THE REMAINDER OF THE FLT WAS UNEVENTFUL. SHORTLY THEREAFTER I WAS RELIEVED BY THE OTHER FO AND BEGAN MY REST BREAK WHICH LASTED UNTIL APPROX 35 MINS BEFORE LNDG. THERE WAS LITTLE DISCUSSION OF THE EVENT, BUT I INFORMED THE CAPT OF MY INTENTION TO FILE THIS RPT.

Data retrieved from NASA's ASRS site as of July 2007 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.