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MD83 crew had an altitude deviation, after the autothrottle system started to close the engine thrust levers. This was a repeat discrepancy.
| Attributes | |
| ACN | 634972 |
| Time | |
| Date | 200410 |
| Day | Sat |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | navaid : lit.vortac |
| State Reference | AR |
| Altitude | msl bound lower : 30500 msl bound upper : 31000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zme.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | MD-83 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Phase | cruise : level descent : vacating altitude |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| ASRS Report | 634972 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| ASRS Report | 634821 |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude maintenance problem : improper maintenance non adherence : far non adherence : company policies non adherence : published procedure other anomaly |
| Independent Detector | aircraft equipment other aircraft equipment : altimeters other controllera other flight crewa other flight crewb |
| Resolutory Action | controller : issued alert flight crew : overcame equipment problem flight crew : overrode automation other |
| Consequence | other other |
| Factors | |
| Maintenance | contributing factor : schedule pressure performance deficiency : repair performance deficiency : testing performance deficiency : non compliance with legal requirements |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance Maintenance Human Performance Company |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation |
Narrative:
Uncommanded airspeed reduction a leveloff. There was a previous write-up in the maintenance log about the aircraft not following specified programmed airspeed inputs that was checked out and signed off. Airspeed/mach were properly set during preflight and thumbwheel and airspeed/mach buttons used during climb to altitude. Right at leveloff from a cruise climb, the throttles came back almost to idle trying to follow an uncommanded 230 KIAS with the airspeed quickly bleeding off to about .72 mach or a little less, and the aircraft started a descent to keep the airspeed. Both autoplt and autothrottles were clicked off and a manual recovery initiated back to altitude but not before losing about 500 ft with a query from center. The aircraft was reset for cruise and worked fine for the remainder of the flight but again written up. The only speeds used to that point were the standard 250 KTS to 10000 ft, 320 KTS to mach and a .75 mach to cruise with no other inputs. The loser airspeed is a mystery to both of us. Supplemental information from acn 634821: the autoplt was transitioning from climb to altitude capture. As soon as the FMA went to altitude capture. As soon as the FMA went to altitude capture, I noticed the navigation window showed navigation hold instead of navigation track. We had been tracking the FMC course. I then looked at the airspeed indicator and the speed was 280 KTS .756 mach. The airspeed bug however had shifted to 230 KTS. When leveloff occurs the airspeed commanded by the bug is what the power goes to. So 100 ft below 310 KTS the power began to retard toward idle. I called out 200 ft low and the captain disengaged the autoplt and pushed up the power smoothly. We wrote up the airplane and this was the 3RD such write-up in recent history.
Original NASA ASRS Text
Title: MD83 CREW HAD AN ALTDEV, AFTER THE AUTOTHROTTLE SYS STARTED TO CLOSE THE ENG THRUST LEVERS. THIS WAS A REPEAT DISCREPANCY.
Narrative: UNCOMMANDED AIRSPD REDUCTION A LEVELOFF. THERE WAS A PREVIOUS WRITE-UP IN THE MAINT LOG ABOUT THE ACFT NOT FOLLOWING SPECIFIED PROGRAMMED AIRSPD INPUTS THAT WAS CHKED OUT AND SIGNED OFF. AIRSPD/MACH WERE PROPERLY SET DURING PREFLT AND THUMBWHEEL AND AIRSPD/MACH BUTTONS USED DURING CLB TO ALT. RIGHT AT LEVELOFF FROM A CRUISE CLB, THE THROTTLES CAME BACK ALMOST TO IDLE TRYING TO FOLLOW AN UNCOMMANDED 230 KIAS WITH THE AIRSPD QUICKLY BLEEDING OFF TO ABOUT .72 MACH OR A LITTLE LESS, AND THE ACFT STARTED A DSCNT TO KEEP THE AIRSPD. BOTH AUTOPLT AND AUTOTHROTTLES WERE CLICKED OFF AND A MANUAL RECOVERY INITIATED BACK TO ALT BUT NOT BEFORE LOSING ABOUT 500 FT WITH A QUERY FROM CTR. THE ACFT WAS RESET FOR CRUISE AND WORKED FINE FOR THE REMAINDER OF THE FLT BUT AGAIN WRITTEN UP. THE ONLY SPDS USED TO THAT POINT WERE THE STANDARD 250 KTS TO 10000 FT, 320 KTS TO MACH AND A .75 MACH TO CRUISE WITH NO OTHER INPUTS. THE LOSER AIRSPD IS A MYSTERY TO BOTH OF US. SUPPLEMENTAL INFO FROM ACN 634821: THE AUTOPLT WAS TRANSITIONING FROM CLB TO ALT CAPTURE. AS SOON AS THE FMA WENT TO ALT CAPTURE. AS SOON AS THE FMA WENT TO ALT CAPTURE, I NOTICED THE NAV WINDOW SHOWED NAV HOLD INSTEAD OF NAV TRACK. WE HAD BEEN TRACKING THE FMC COURSE. I THEN LOOKED AT THE AIRSPD INDICATOR AND THE SPD WAS 280 KTS .756 MACH. THE AIRSPD BUG HOWEVER HAD SHIFTED TO 230 KTS. WHEN LEVELOFF OCCURS THE AIRSPD COMMANDED BY THE BUG IS WHAT THE PWR GOES TO. SO 100 FT BELOW 310 KTS THE PWR BEGAN TO RETARD TOWARD IDLE. I CALLED OUT 200 FT LOW AND THE CAPT DISENGAGED THE AUTOPLT AND PUSHED UP THE PWR SMOOTHLY. WE WROTE UP THE AIRPLANE AND THIS WAS THE 3RD SUCH WRITE-UP IN RECENT HISTORY.
Data retrieved from NASA's ASRS site as of July 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.