Narrative:

The event occurred while making a turn with the autoplt turn knob through about 40-50 degree using 10-12 degrees angle of bank. During this turn I was distracted for a few seconds by 'waypoint paperwork'. The autoplt failed to hold altitude and while remaining engaged, began a 500-800 FPM descent. The descent was noticed at about 300' below assigned altitude, however, speed had already built up to M .83 or M .84. At the moment that I reached for the controls to recover, my attitude gyro tumbled leaving me with no pitch reference. High speed mach buffet was experienced and the captain recovered from the descent with a total altitude loss of 1000'. No traffic conflict from the descent was noted. Several factors were contributing: 1) there had been several previous writeups of autoplt pitch malfunctions. However, the autoplt had been MEL'ed with pitch trim inoperative. On all previous segments of this trip (16 hours), when the pitch trim failed, the autoplt disconnected with the associated aural and visual warning -- much less of a problem than diving with no warning. With the pitch trim inoperative, the autoplt should not have been used at all. 2) the first officer's attitude gyro had been tumbling on previous segments. The mechanic swapped gyro's but the captain had elected not to write this up due to lack of spares. 3) the altitude alert had been activating randomly even though altitude was correct, leading to a tendency not to be as alert to it (a 'boy cries wolf' problem). Again not written up due to randomness. As of this writing almost a month later, the aircraft is still flying with no autoplt pitch and a sick altitude alerter. This is in violation of MEL rules and safety and should not continue!

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Original NASA ASRS Text

Title: FO FLYING HVT AT FL390 MAKING A TURN WITH TURN KNOB ON AUTOPLT, ACFT LOST ALT AND ATTITUDE GYRO TUMBLED.

Narrative: THE EVENT OCCURRED WHILE MAKING A TURN WITH THE AUTOPLT TURN KNOB THROUGH ABOUT 40-50 DEG USING 10-12 DEGS ANGLE OF BANK. DURING THIS TURN I WAS DISTRACTED FOR A FEW SECONDS BY 'WAYPOINT PAPERWORK'. THE AUTOPLT FAILED TO HOLD ALT AND WHILE REMAINING ENGAGED, BEGAN A 500-800 FPM DSCNT. THE DSCNT WAS NOTICED AT ABOUT 300' BELOW ASSIGNED ALT, HOWEVER, SPEED HAD ALREADY BUILT UP TO M .83 OR M .84. AT THE MOMENT THAT I REACHED FOR THE CONTROLS TO RECOVER, MY ATTITUDE GYRO TUMBLED LEAVING ME WITH NO PITCH REFERENCE. HIGH SPEED MACH BUFFET WAS EXPERIENCED AND THE CAPT RECOVERED FROM THE DSCNT WITH A TOTAL ALT LOSS OF 1000'. NO TFC CONFLICT FROM THE DSCNT WAS NOTED. SEVERAL FACTORS WERE CONTRIBUTING: 1) THERE HAD BEEN SEVERAL PREVIOUS WRITEUPS OF AUTOPLT PITCH MALFUNCTIONS. HOWEVER, THE AUTOPLT HAD BEEN MEL'ED WITH PITCH TRIM INOP. ON ALL PREVIOUS SEGMENTS OF THIS TRIP (16 HRS), WHEN THE PITCH TRIM FAILED, THE AUTOPLT DISCONNECTED WITH THE ASSOCIATED AURAL AND VISUAL WARNING -- MUCH LESS OF A PROBLEM THAN DIVING WITH NO WARNING. WITH THE PITCH TRIM INOP, THE AUTOPLT SHOULD NOT HAVE BEEN USED AT ALL. 2) THE F/O'S ATTITUDE GYRO HAD BEEN TUMBLING ON PREVIOUS SEGMENTS. THE MECHANIC SWAPPED GYRO'S BUT THE CAPT HAD ELECTED NOT TO WRITE THIS UP DUE TO LACK OF SPARES. 3) THE ALT ALERT HAD BEEN ACTIVATING RANDOMLY EVEN THOUGH ALT WAS CORRECT, LEADING TO A TENDENCY NOT TO BE AS ALERT TO IT (A 'BOY CRIES WOLF' PROBLEM). AGAIN NOT WRITTEN UP DUE TO RANDOMNESS. AS OF THIS WRITING ALMOST A MONTH LATER, THE ACFT IS STILL FLYING WITH NO AUTOPLT PITCH AND A SICK ALT ALERTER. THIS IS IN VIOLATION OF MEL RULES AND SAFETY AND SHOULD NOT CONTINUE!

Data retrieved from NASA's ASRS site as of August 2007 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.