Narrative:

Descended from FL410 ot assigned FL240 with clearance to hold at bunker intersection en route to msp. Used vertical speed and speed intervene on mode control panel. Msp ATC requested we level at FL330. We did so. We got altitude capture and I was satisfied we were at FL330 and checked airspeed. I was satisfied that it was at 220 KTS as I had selected. I then proceeded to verify that the FMC was properly programmed to hold at bunker intersection as directed. While checking FMC we experienced the stick shaker. I manually went to full power and noted airspeed to be quite low, approximately 140 KTS. I took aircraft off the autoplt and proceeded to fly the aircraft out of the pending stall. We lost 300-400' of altitude and copilot informed msp ATC we were off altitude and correcting. Msp ATC cleared flight to FL290 at that time and we proceeded to complete airspeed correction during our descent to FL290. We had 2 more dscnts while holding and we tried to recreate the circumstances that led to the lost of airspeed problem. The aircraft and systems seemed to function normally. My personal evaluation is: that while I was in speed intervention on the mode control panel during the initial descent phase the aircraft ended up not being in a speed mode when we leveled off at FL330. The aircraft system responded to commands during descent from FL410, but failed to maintain selected airspeed when at FL330. Selected modes were not changed. Altitude capture/altitude hold was verified. I remained in speed intervene and consciously verified airspeed indicator on the salmon airspeed bug prior to shifting my attention to the FMC panel to check holding programming. I visually checked altitude capture/altitude hold on pitch mode status on ADI. Though I checked airspeed intervene, airspeed indicator, salmon bug, and general cockpit environment, I cannot actually remember checking the autothrottle status/mode on the same primary ADI instrument when I checked altitude capture/altitude hold. That the prestall stick shaker is a valuable assist to safety. That I, the PF, failed to properly monitor the flight instruments. That how the aircraft got out of speed mode is not known to me. Supplemental information from acn 103889: in closing due to the high workload in the cockpit (captain was reviewing the holding pattern and I was programming the computer) we allowed the automation to fly the aircraft. The captain had ensured that the aircraft leveled prior to reviewing the hold. Autothrottles did not engage and speed decreased to stick shaker.

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Original NASA ASRS Text

Title: ACR LGT GETS INTO APCH TO STALL AND ALT EXCURSION WHEN AUTO THROTTLES DO NOT MAINTAIN SPEED.

Narrative: DSNDED FROM FL410 OT ASSIGNED FL240 WITH CLRNC TO HOLD AT BUNKER INTXN ENRTE TO MSP. USED VERT SPD AND SPD INTERVENE ON MODE CONTROL PANEL. MSP ATC REQUESTED WE LEVEL AT FL330. WE DID SO. WE GOT ALT CAPTURE AND I WAS SATISFIED WE WERE AT FL330 AND CHKED AIRSPD. I WAS SATISFIED THAT IT WAS AT 220 KTS AS I HAD SELECTED. I THEN PROCEEDED TO VERIFY THAT THE FMC WAS PROPERLY PROGRAMMED TO HOLD AT BUNKER INTXN AS DIRECTED. WHILE CHKING FMC WE EXPERIENCED THE STICK SHAKER. I MANUALLY WENT TO FULL PWR AND NOTED AIRSPD TO BE QUITE LOW, APPROX 140 KTS. I TOOK ACFT OFF THE AUTOPLT AND PROCEEDED TO FLY THE ACFT OUT OF THE PENDING STALL. WE LOST 300-400' OF ALT AND COPLT INFORMED MSP ATC WE WERE OFF ALT AND CORRECTING. MSP ATC CLRED FLT TO FL290 AT THAT TIME AND WE PROCEEDED TO COMPLETE AIRSPD CORRECTION DURING OUR DSCNT TO FL290. WE HAD 2 MORE DSCNTS WHILE HOLDING AND WE TRIED TO RECREATE THE CIRCUMSTANCES THAT LED TO THE LOST OF AIRSPD PROB. THE ACFT AND SYSTEMS SEEMED TO FUNCTION NORMALLY. MY PERSONAL EVALUATION IS: THAT WHILE I WAS IN SPD INTERVENTION ON THE MODE CONTROL PANEL DURING THE INITIAL DSCNT PHASE THE ACFT ENDED UP NOT BEING IN A SPD MODE WHEN WE LEVELED OFF AT FL330. THE ACFT SYS RESPONDED TO COMMANDS DURING DSCNT FROM FL410, BUT FAILED TO MAINTAIN SELECTED AIRSPD WHEN AT FL330. SELECTED MODES WERE NOT CHANGED. ALT CAPTURE/ALT HOLD WAS VERIFIED. I REMAINED IN SPD INTERVENE AND CONSCIOUSLY VERIFIED AIRSPD INDICATOR ON THE SALMON AIRSPD BUG PRIOR TO SHIFTING MY ATTN TO THE FMC PANEL TO CHK HOLDING PROGRAMMING. I VISUALLY CHKED ALT CAPTURE/ALT HOLD ON PITCH MODE STATUS ON ADI. THOUGH I CHKED AIRSPD INTERVENE, AIRSPD INDICATOR, SALMON BUG, AND GENERAL COCKPIT ENVIRONMENT, I CANNOT ACTUALLY REMEMBER CHKING THE AUTOTHROTTLE STATUS/MODE ON THE SAME PRIMARY ADI INSTRUMENT WHEN I CHKED ALT CAPTURE/ALT HOLD. THAT THE PRESTALL STICK SHAKER IS A VALUABLE ASSIST TO SAFETY. THAT I, THE PF, FAILED TO PROPERLY MONITOR THE FLT INSTRUMENTS. THAT HOW THE ACFT GOT OUT OF SPD MODE IS NOT KNOWN TO ME. SUPPLEMENTAL INFO FROM ACN 103889: IN CLOSING DUE TO THE HIGH WORKLOAD IN THE COCKPIT (CAPT WAS REVIEWING THE HOLDING PATTERN AND I WAS PROGRAMMING THE COMPUTER) WE ALLOWED THE AUTOMATION TO FLY THE ACFT. THE CAPT HAD ENSURED THAT THE ACFT LEVELED PRIOR TO REVIEWING THE HOLD. AUTOTHROTTLES DID NOT ENGAGE AND SPD DECREASED TO STICK SHAKER.

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.