 |
37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
|
Widebody freight aircraft exhibited autopilot malfunctions during flight. During approach; flight crew disconnected the autopilot when it became apparent that it would overshoot the level-off altitude.
| Attributes | |
| ACN | 761927 |
| Time | |
| Date | 200711 |
| Local Time Of Day | 1801 To 2400 |
| Place | |
| Locale Reference | airport : zzz.airport |
| State Reference | US |
| Altitude | msl single value : 4000 |
| Environment | |
| Flight Conditions | Mixed |
| Light | Night |
| Aircraft 1 | |
| Controlling Facilities | tracon : zzz.tracon |
| Operator | common carrier : air carrier |
| Make Model Name | MD-11 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent : intermediate altitude |
| Route In Use | arrival : on vectors |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 150 flight time total : 15000 flight time type : 2000 |
| ASRS Report | 761927 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : flight engineer pilot : instrument pilot : multi engine pilot : private pilot : commercial pilot : atp |
| Experience | flight time last 90 days : 100 flight time total : 4000 flight time type : 1000 |
| ASRS Report | 761407 |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance maintenance problem : improper maintenance |
| Independent Detector | other flight crewa other flight crewb |
| Resolutory Action | flight crew : overcame equipment problem flight crew : returned to assigned altitude |
| Supplementary | |
| Problem Areas | Aircraft FAA |
| Primary Problem | Aircraft |
Narrative:
We were on the final portion of a 9+35 flight. En route; we had a couple of hard jolts on the autoplt at altitude. We felt something was going on within the autoplt system that we should watch. We eventually changed to the #2 system; which seemed to respond normally the rest of the way across the pacific. During descent; we again got several jolts on the autoplt but it did not disconnect. I switched back and forth from #1 to #2 autoplt attempting to see which system would be our best option for the approach. At about 12000 ft we got the first of several stabilizer out of trim alerts. We looked up the alert and knew that when disconnecting the autoplt the aircraft may be out of trim. We disconnected the autoplt once to see if the trim was going to be ok. It seemed to be reasonably trimmed; and was responding normally to manual trim so the autoplt was again connected. We were in and out of the clouds after a long flight across the pacific; so I felt the best option was to use the autoplt if we felt comfortable that one of the system was going to function adequately. We were given a descent to 4000 ft. As we approached that altitude; the autoplt seemed to be performing ok; but as we approached the leveloff point; it became obvious that the aircraft was not going to level as required. Again with a stabilizer out of trim alert we disconnected the autoplt to level off; but with the trim still a little out of neutral the aircraft descended about 200-250 ft below our leveloff altitude. We immediately climbed back to altitude and leveled off. At this point we decided to just fly the approach with the autoplt off. Approach control neither asked nor noted any altitude deviation to us. The first officer was very helpful during this entire process both calling out deviations and backing up on headings and altitudes during the autoplt off operation of the aircraft. The aircraft was written up. This incident illustrates to me the gray area that exists; transitioning between wanting to stay with the automation; which you know under normal circumstances flies very precise parameters; and the decision to eliminate the automation and fly the aircraft.
Original NASA ASRS Text
Title: WIDEBODY FREIGHT ACFT EXHIBITED AUTOPILOT MALFUNCTIONS DURING FLT. DURING APCH; FLT CREW DISCONNECTED THE AUTOPILOT WHEN IT BECAME APPARENT THAT IT WOULD OVERSHOOT THE LEVEL-OFF ALT.
Narrative: WE WERE ON THE FINAL PORTION OF A 9+35 FLT. ENRTE; WE HAD A COUPLE OF HARD JOLTS ON THE AUTOPLT AT ALT. WE FELT SOMETHING WAS GOING ON WITHIN THE AUTOPLT SYS THAT WE SHOULD WATCH. WE EVENTUALLY CHANGED TO THE #2 SYS; WHICH SEEMED TO RESPOND NORMALLY THE REST OF THE WAY ACROSS THE PACIFIC. DURING DSCNT; WE AGAIN GOT SEVERAL JOLTS ON THE AUTOPLT BUT IT DID NOT DISCONNECT. I SWITCHED BACK AND FORTH FROM #1 TO #2 AUTOPLT ATTEMPTING TO SEE WHICH SYS WOULD BE OUR BEST OPTION FOR THE APCH. AT ABOUT 12000 FT WE GOT THE FIRST OF SEVERAL STABILIZER OUT OF TRIM ALERTS. WE LOOKED UP THE ALERT AND KNEW THAT WHEN DISCONNECTING THE AUTOPLT THE ACFT MAY BE OUT OF TRIM. WE DISCONNECTED THE AUTOPLT ONCE TO SEE IF THE TRIM WAS GOING TO BE OK. IT SEEMED TO BE REASONABLY TRIMMED; AND WAS RESPONDING NORMALLY TO MANUAL TRIM SO THE AUTOPLT WAS AGAIN CONNECTED. WE WERE IN AND OUT OF THE CLOUDS AFTER A LONG FLT ACROSS THE PACIFIC; SO I FELT THE BEST OPTION WAS TO USE THE AUTOPLT IF WE FELT COMFORTABLE THAT ONE OF THE SYS WAS GOING TO FUNCTION ADEQUATELY. WE WERE GIVEN A DSCNT TO 4000 FT. AS WE APCHED THAT ALT; THE AUTOPLT SEEMED TO BE PERFORMING OK; BUT AS WE APCHED THE LEVELOFF POINT; IT BECAME OBVIOUS THAT THE ACFT WAS NOT GOING TO LEVEL AS REQUIRED. AGAIN WITH A STABILIZER OUT OF TRIM ALERT WE DISCONNECTED THE AUTOPLT TO LEVEL OFF; BUT WITH THE TRIM STILL A LITTLE OUT OF NEUTRAL THE ACFT DSNDED ABOUT 200-250 FT BELOW OUR LEVELOFF ALT. WE IMMEDIATELY CLBED BACK TO ALT AND LEVELED OFF. AT THIS POINT WE DECIDED TO JUST FLY THE APCH WITH THE AUTOPLT OFF. APCH CTL NEITHER ASKED NOR NOTED ANY ALTDEV TO US. THE FO WAS VERY HELPFUL DURING THIS ENTIRE PROCESS BOTH CALLING OUT DEVS AND BACKING UP ON HDGS AND ALTS DURING THE AUTOPLT OFF OP OF THE ACFT. THE ACFT WAS WRITTEN UP. THIS INCIDENT ILLUSTRATES TO ME THE GRAY AREA THAT EXISTS; TRANSITIONING BTWN WANTING TO STAY WITH THE AUTOMATION; WHICH YOU KNOW UNDER NORMAL CIRCUMSTANCES FLIES VERY PRECISE PARAMETERS; AND THE DECISION TO ELIMINATE THE AUTOMATION AND FLY THE ACFT.
Data retrieved from NASA's ASRS site as of January 2009 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.