B757 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Flight Deck / Cabin / Aircraft Event Illness / Injury; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Loss Of Aircraft Control
Air Traffic Control Provided Assistance; Flight Crew Regained Aircraft Control; Flight Crew Returned To Departure Airport; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed in Emergency Condition; General Physical Injury / Incapacitation
Weather
Approximately 10-15 mins after takeoff we encountered severe turbulence between 27;000- 30;000 feet. Duration was approximately 5 minutes. It was the worst turbulence I have encountered in my 35 years of flying.There had been no other aircraft on our frequencies mentioning severe turbulence. There was no convective activity in the area; although very high winds on the ground and aloft; associated with a cold front. The seat belt sign was turned on; passengers were all seated. The flight attendants in the back had just got their carts out to begin their service. Severe turbulence began without warning. The [Relief Officer] had just gone back to business class to begin his break. Both Captain and First Officer (FO) had our hands full to maintain aircraft control. FO was pilot flying. We disconnected Auto Pilot and Auto Throttles; and attempted to climb out of the turbulence. It took us longer than expected; due to previously mentioned lack of complete aircraft control. Airspeed loss was approximately 60 knots; from 310 down to 250 before airspeed decay was arrested and a climb to smooth air was accomplished when aircraft was safely under control.I immediately called the cabin on interphone to assess. I heard crying and reports of multiple seriously injured flight attendants. I immediately asked for return to the departure airport. The [Relief Officer] remained in the cabin to help with the injured crew members. One women had a head wound and the other; who was more seriously injured; had a flying full food service cart land on her. As soon as injured were as stable as possible; [Relief Officer] returned to cockpit to aid in our return. I was concerned with descending back thru the turbulence area; so we flew south for 30 miles or so; before turning back west towards the departure airport. We were able to miss the turbulence on descent. We were going to be over weight by about 20;000 lbs; so we accomplished the Over Weight Landing checklist. We radioed ops and had ambulances waiting for us at gate.We asked for; and received; clearance to straight in ILS. Weather was clear and wind was well within limits. Uneventful approach and landing on the long runway; with minimal brake usage; due to over weight condition. ATC was outstanding through the entire event; enroute; approach; tower and ground. Arrived at gate; passengers remained seated to allow EMTs to get to rear of aircraft. Injured crew safely removed and passengers allowed to deplane. Many frightened; scared passengers. Cabin crew was injured; very emotionally upset; but still performed their duties admirably.The three of us pilots were very keyed-up and over-loaded on adrenaline after what we had been thru; and after a brief; closed door conference; the three of us decided that we were not mentally or physically fit for duty to fly an 8 hour flight forecast into heavy winds with possible missed approach and/or diversion. Along with the outstanding cabin crew; I would like to commend my two FOs. They were invaluable to the safe completion of this flight.
During cruise climb after takeoff the aircraft encountered severe clear air turbulence. The event incurred cabin crew injuries and the flight returned to originating airport.