B737-800
Flight Crew Air Transport Pilot (ATP)
Deviation - Altitude Excursion From Assigned Altitude; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Loss Of Aircraft Control; Inflight Event / Encounter Weather / Turbulence
General Declared Emergency
Environment - Non Weather Related; Weather
We were on top of a cloud deck and skimming the top with light to occasional moderate turbulence. We both discussed going to FL400 to get above the tops. We were cleared to FL400 out of FL380. Going through FL388 we experienced heavy moderate turbulence and the aircraft would no longer climb and we began an uncontrolled descent. The Captain said to declare an emergency to clear the airspace below us as I told Center we were descending to FL350. At no time were we near stall speed. The Captain disengaged the autopilot and hand flew it to FL350. ATC never asked us to fill in the blanks for the emergency declaration so I believe it never became official. I explained to them what we experienced and they said continue on. We polled the flight attendants and everyone was fine. We continued to destination and landed uneventfully.In hindsight I should have not gone to up to FL400 with the possibility of turbulence in the area. It was just too high for those conditions.
A B737NG flight crew opted to try and climb above turbulence at their cruise altitude of FL380 and were cleared to FL400. Climbing through FL390 they encountered even greater turbulence and the aircraft could climb no higher; in fact entered an uncommanded descent. The crew declared an emergency and descended to FL350 for the uneventful remainder of their scheduled flight.