Narrative:

I; copilot; was flying aircraft. Thunderstorms and icing were active in the area. Radar was on and aircraft was on a clear flight path in smooth air. Flight was running late so a modified climb speed of 310 was being used and a final altitude of 24;000 ft was requested from ATC due to a short leg length. Climbing through 18;000 ft both altimeters were switched to standard; autopilot was engaged at this time and lights were secured. At approximately 19;000 ft in the climb the pitch bar on the pfd disappeared and the aircraft pitched over hard from approximately seven degrees nose up to five degrees nose down. I disengaged the autopilot and auto throttles and slowly brought the deck angle back into a climb attitude. No column entanglement was apparent. No warning lights or messages were present. Windshield; pitot heat and engine anti-ice were on and icing was present on the wipers. Aircraft increased in speed very rapidly and mach clacker sounded at 325 KTS during pull and recovery. Aircraft was returned to flight path and a slower airspeed used. Flight attendants were not injured; felt like a hard level off. Maintenance was informed of problem and met the aircraft on jet bridge. Long and descriptive log book entry was completed by captain. Mechanic was debriefed and after an hour; called the captain with preliminary information. Two faults were found. An altitude discrepancy was found as a hard fault and a right adiru fault was indicated. His opinion was icing of the right pitot. Again heat was on and no fault was indicated. Issues: deviation from ATC clearance during pitch over and subsequent recovery. Aircraft exceeded vmmo during recovery by about 5 KTS.

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Original NASA ASRS Text

Title: A B737-800 pilot reported a pitch over climbing to FL190 resulting in a 4;000' altitude loss. Maintenance reported an ADIRU fault with an altitude fault.

Narrative: I; copilot; was flying aircraft. Thunderstorms and icing were active in the area. Radar was on and aircraft was on a clear flight path in smooth air. Flight was running late so a modified climb speed of 310 was being used and a final altitude of 24;000 FT was requested from ATC due to a short leg length. Climbing through 18;000 FT both altimeters were switched to STD; autopilot was engaged at this time and lights were secured. At approximately 19;000 FT in the climb the pitch bar on the PFD disappeared and the aircraft pitched over hard from approximately seven degrees nose up to five degrees nose down. I disengaged the autopilot and auto throttles and slowly brought the deck angle back into a climb attitude. No column entanglement was apparent. No warning lights or messages were present. Windshield; pitot heat and engine anti-ice were ON and icing was present on the wipers. Aircraft increased in speed very rapidly and mach clacker sounded at 325 KTS during pull and recovery. Aircraft was returned to flight path and a slower airspeed used. Flight Attendants were not injured; felt like a hard level off. Maintenance was informed of problem and met the aircraft on jet bridge. Long and descriptive log book entry was completed by Captain. Mechanic was debriefed and after an hour; called the Captain with preliminary information. Two faults were found. An altitude discrepancy was found as a hard fault and a right ADIRU fault was indicated. His opinion was icing of the right pitot. Again heat was ON and no fault was indicated. Issues: Deviation from ATC clearance during pitch over and subsequent recovery. Aircraft exceeded VMMO during recovery by about 5 KTS.

Data retrieved from NASA's ASRS site as of April 2012 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.