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A B737-300 crew had a chronic 'stabilizer out of trim' for the 'a' autoplt. They had a 500 ft altitude deviation as a result.
| Attributes | |
| ACN | 607219 |
| Time | |
| Date | 200402 |
| Day | Fri |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | navaid : tch.vortac |
| State Reference | UT |
| Altitude | msl bound lower : 13500 msl bound upper : 14000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | tracon : s56.tracon |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other other vortac |
| Flight Phase | descent : intermediate altitude |
| Route In Use | arrival star : jammn |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time last 90 days : 180 flight time total : 10500 flight time type : 8000 |
| ASRS Report | 607219 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Experience | flight time last 90 days : 24 |
| ASRS Report | 607220 |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : excursion from assigned altitude maintenance problem : improper maintenance non adherence : clearance |
| Independent Detector | aircraft equipment other aircraft equipment : altimeters stab out of trim light other flight crewa other flight crewb |
| Resolutory Action | flight crew : returned to assigned altitude other |
| Consequence | other other |
| Factors | |
| Maintenance | contributing factor : schedule pressure performance deficiency : fault isolation performance deficiency : testing performance deficiency : repair performance deficiency : non compliance with legal requirements |
| Supplementary | |
| Problem Areas | Aircraft Company Flight Crew Human Performance |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
The aircraft was level at 14000 ft on the jammn 4 arrival. I, the captain, was flying. The 'a' autoplt/command mode and LNAV were in use. I and the first officer pulled out our approach and airfield diagrams to further discuss the landing and taxi in at salt lake. As I looked up from my airfield diagram, I was shocked to see the aircraft at approximately 13600-13500 ft and smoothly descending. The autoplt was still engaged, no descent mode was selected and no audio or visual alarms or indications were present. As I quickly returned the aircraft to 14000 ft, I noticed a flicker of the stabilizer out of trim light. We informed ATC we were having autoplt problem. The aircraft operated normally on the 'B' autoplt. We reviewed the QRH and notified maintenance upon landing. Maintenance indicated the aircraft had a history of 'a' autoplt/stabilizer out of trim problems. The 'a' autoplt was then MEL'ed inoperative. We flew the rest of the day on 'B' autoplt without incident. This is a very insidious and potentially dangerous malfunction. Possibly if the first officer and I were not both looking at the approach plate at the same time the altitude deviation and descent could have been detected and corrected sooner. A heads up, heads down, call between the first officer and I might minimize the chance of this happening again in the future.
Original NASA ASRS Text
Title: A B737-300 CREW HAD A CHRONIC 'STABILIZER OUT OF TRIM' FOR THE 'A' AUTOPLT. THEY HAD A 500 FT ALTDEV AS A RESULT.
Narrative: THE ACFT WAS LEVEL AT 14000 FT ON THE JAMMN 4 ARR. I, THE CAPT, WAS FLYING. THE 'A' AUTOPLT/COMMAND MODE AND LNAV WERE IN USE. I AND THE FO PULLED OUT OUR APCH AND AIRFIELD DIAGRAMS TO FURTHER DISCUSS THE LNDG AND TAXI IN AT SALT LAKE. AS I LOOKED UP FROM MY AIRFIELD DIAGRAM, I WAS SHOCKED TO SEE THE ACFT AT APPROX 13600-13500 FT AND SMOOTHLY DSNDING. THE AUTOPLT WAS STILL ENGAGED, NO DSCNT MODE WAS SELECTED AND NO AUDIO OR VISUAL ALARMS OR INDICATIONS WERE PRESENT. AS I QUICKLY RETURNED THE ACFT TO 14000 FT, I NOTICED A FLICKER OF THE STABILIZER OUT OF TRIM LIGHT. WE INFORMED ATC WE WERE HAVING AUTOPLT PROB. THE ACFT OPERATED NORMALLY ON THE 'B' AUTOPLT. WE REVIEWED THE QRH AND NOTIFIED MAINT UPON LNDG. MAINT INDICATED THE ACFT HAD A HISTORY OF 'A' AUTOPLT/STABILIZER OUT OF TRIM PROBS. THE 'A' AUTOPLT WAS THEN MEL'ED INOP. WE FLEW THE REST OF THE DAY ON 'B' AUTOPLT WITHOUT INCIDENT. THIS IS A VERY INSIDIOUS AND POTENTIALLY DANGEROUS MALFUNCTION. POSSIBLY IF THE FO AND I WERE NOT BOTH LOOKING AT THE APCH PLATE AT THE SAME TIME THE ALTDEV AND DSCNT COULD HAVE BEEN DETECTED AND CORRECTED SOONER. A HEADS UP, HEADS DOWN, CALL BTWN THE FO AND I MIGHT MINIMIZE THE CHANCE OF THIS HAPPENING AGAIN IN THE FUTURE.
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.