A boeing 737 flight crew reported experiencing severe turbulence while on an oceanic flight plan. Th...

Narrative:

Departed on time; experienced light turbulence for the first 4 hours of flight. About 2 1/2 hours into flight (FL350); we had pockets of moderate chop. We were told of continuous moderate about 100 west of fix ZZZZ until well beyond ZZZZ1 at our altitude. We requested FL290; but arinc denied us due to company flight off our right and 1;000 below. We told ATC we could see traffic and could maintain visual; but they didn't care.not 10 minutes later we began experiencing continuous moderate turbulence with pockets of severe. It quickly migrated to continuous severe turbulence with altitude and airspeed deviations (+/- 100 feet and +/- 15 knots). We were also unable to view instruments any more.we then turned right about 60 degrees and left our offset track and descended to FL290; then FL270 as the ride at FL290 was still intolerable. At the same time; the other company flight executed a turn to the left and descended as well. They also encountered severe turbulence.we broadcast our actions on 121.5 and 123.45. As the event began to end we attempted dispatch and ATC to let them know as well and attempted to get a new clearance back to our filed track.there were no injuries. There were some sick passengers. If it weren't for the captain staying on top of the PA announcements and a great cabin crew enforcing them I believe the outcome would have been different.we eventually landed at [our destination] 10 minutes early to a round of applause and 1;000 thank yous for a great flight.learning what took place: the extended range twin operations (ETOPS) procedures work. They work well. ATC is a source; but with 1940's technology you may be on our own. Also; multiple seatbelt announcements are vital as there is always some passenger that thinks we are overselling the turbulence problem and feels it is okay to get up and get something out of the overhead bin. Situational awareness is key. Don't start thinking about what you want to do as the event happens. Have an escape plan in your back pocket always.

Original NASA ASRS Text

Title: A Boeing 737 flight crew reported experiencing severe turbulence while on an oceanic flight plan. The captain exercised emergency authority; turned off course and descended to a smoother altitude. This action was done in accordance with established overwater emergency procedures.

Narrative: Departed on time; experienced light turbulence for the first 4 hours of flight. About 2 1/2 hours into flight (FL350); we had pockets of moderate chop. We were told of continuous moderate about 100 west of fix ZZZZ until well beyond ZZZZ1 at our altitude. We requested FL290; but ARINC denied us due to company flight off our right and 1;000 below. We told ATC we could see traffic and could maintain visual; but they didn't care.Not 10 minutes later we began experiencing continuous moderate turbulence with pockets of severe. It quickly migrated to continuous severe turbulence with altitude and airspeed deviations (+/- 100 feet and +/- 15 knots). We were also unable to view instruments any more.We then turned right about 60 degrees and left our offset track and descended to FL290; then FL270 as the ride at FL290 was still intolerable. At the same time; the other company flight executed a turn to the left and descended as well. They also encountered severe turbulence.We broadcast our actions on 121.5 and 123.45. As the event began to end we attempted dispatch and ATC to let them know as well and attempted to get a new clearance back to our filed track.There were no injuries. There were some sick passengers. If it weren't for the Captain staying on top of the PA announcements and a great cabin crew enforcing them I believe the outcome would have been different.We eventually landed at [our destination] 10 minutes early to a round of applause and 1;000 thank yous for a great flight.Learning what took place: the Extended Range Twin Operations (ETOPS) procedures work. They work well. ATC is a source; but with 1940's technology you may be on our own. Also; multiple seatbelt announcements are vital as there is always some passenger that thinks we are overselling the turbulence problem and feels it is okay to get up and get something out of the overhead bin. Situational awareness is key. Don't start thinking about what you want to do as the event happens. Have an escape plan in your back pocket always.

Data retrieved from NASA's ASRS site 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	1324626
Time
Date	201601
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Route In Use	Oceanic
Flight Plan	IFR
Person 1
Function	First Officer Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Deviation - Altitude Excursion From Assigned Altitude Deviation - Speed All Types Deviation - Track / Heading All Types Flight Deck / Cabin / Aircraft Event Illness Inflight Event / Encounter Weather / Turbulence

A boeing 737 flight crew reported experiencing severe turbulence while on an oceanic flight plan. The captain exercised emergency authority; turned off course and descended to a smoother altitude. This action was done in accordance with established overwater emergency procedures.