A widebodied freighter encountered severe turbulence at FL380 which resulted in the autopilot discon...

Narrative:

Enroute approximately at FL380 we encountered severe turbulence for approximately 20 seconds. During the encounter we experienced a strong updraft that caused the autopilot to disconnect and the aircraft to climb rapidly. The pilot flying (PF) immediately hand flew the airplane and stopped the aircraft assent at FL38.5 and returned the aircraft to FL380. During the event I informed center that we were in severe turbulence attempting to exit and the aircraft climbed briefly and we were recovering; the altitude deviation lasted no more than 5 seconds. Prior to the event we were in VMC and smooth air with some thunderstorms south and southeast of our route of flight; the radar showed nothing in front of us and no other aircraft in the vicinity or ATC mentioned any turbulence. Also; the HUD and efvs (enhanced flight vision system) were MEL'd and completely inoperative. The turbulence event was a complete surprise. We also reported the encounter to aircraft maintenance via ACARS and a maintenance log entry. Due to the severity of the turbulence and the strong updraft the autopilot disengaged causing the aircraft to rapidly ascend before the PF could make a correction. If the efvs had been functioning it is possible the PF could have seen whatever caused our severe turbulence and we could have avoided it. More advanced WX radar equipment that is now commercially available may have also detected it and allowed for avoidance.

Original NASA ASRS Text

Title: A widebodied freighter encountered severe turbulence at FL380 which resulted in the autopilot disconnecting and a 500 feet climb. The HUD and Enhanced Flight Vision System (EFVS) were both inoperative.

Narrative: Enroute approximately at FL380 we encountered severe turbulence for approximately 20 seconds. During the encounter we experienced a strong updraft that caused the autopilot to disconnect and the aircraft to climb rapidly. The Pilot Flying (PF) immediately hand flew the airplane and stopped the aircraft assent at FL38.5 and returned the aircraft to FL380. During the event I informed Center that we were in severe turbulence attempting to exit and the aircraft climbed briefly and we were recovering; the altitude deviation lasted no more than 5 seconds. Prior to the event we were in VMC and smooth air with some thunderstorms South and Southeast of our route of flight; the radar showed nothing in front of us and no other aircraft in the vicinity or ATC mentioned any turbulence. Also; the HUD and EFVS (Enhanced Flight Vision System) were MEL'd and completely inoperative. The turbulence event was a complete surprise. We also reported the encounter to aircraft maintenance via ACARS and a maintenance log entry. Due to the severity of the turbulence and the strong updraft the autopilot disengaged causing the aircraft to rapidly ascend before the PF could make a correction. If the EFVS had been functioning it is possible the PF could have seen whatever caused our severe turbulence and we could have avoided it. More advanced WX Radar equipment that is now commercially available may have also detected it and allowed for avoidance.

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	1199443
Time
Date	201408
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Make Model Name	Large Transport
Operating Under FAR Part	Part 121
Flight Phase	Cruise
Flight Plan	IFR
Person 1
Function	First Officer Pilot Not Flying
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Inflight Event / Encounter Weather / Turbulence

A widebodied freighter encountered severe turbulence at FL380 which resulted in the autopilot disconnecting and a 500 feet climb. The HUD and enhanced flight vision system (efvs) were both inoperative.