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Reported altitude deviation when aircraft descended below assigned altitude apparently due to autoplt problem.
| Attributes | |
| ACN | 388280 |
| Time | |
| Date | 199712 |
| Day | Tue |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : slc |
| State Reference | UT |
| Altitude | msl bound lower : 30600 msl bound upper : 31000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zlc |
| Operator | common carrier : air carrier |
| Make Model Name | B737-300 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | Other |
| Flight Phase | cruise other cruise other |
| Route In Use | enroute : on vectors |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp pilot : flight engineer |
| Experience | flight time last 90 days : 150 flight time total : 11000 flight time type : 220 |
| ASRS Report | 388280 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp pilot : commercial pilot : flight engineer pilot : instrument pilot : private |
| Experience | flight time last 90 days : 200 flight time total : 4500 flight time type : 800 |
| ASRS Report | 389301 |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance |
| Independent Detector | other flight crewa |
| Resolutory Action | flight crew : regained aircraft control flight crew : returned to intended course or assigned course other |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation |
Narrative:
In cruise at FL310, first officer flying, autoplt on, LNAV on, VNAV on, first officer is briefing ILS DME runway 34L approach to slc. When first officer notices aircraft descending very slowly passing through FL306, first officer immediately kicked off autoplt, hand flew aircraft back to FL310. Tried 'a' and 'B' autoplts, no help. Aircraft was too erratic to fly in pitch so he hand flew it. Later, discovered a flight control 'speed trim fail.' no comment was made to us about altitude deviation. Rest of flight uneventful.
Original NASA ASRS Text
Title: RPTED ALTDEV WHEN ACFT DSNDED BELOW ASSIGNED ALT APPARENTLY DUE TO AUTOPLT PROB.
Narrative: IN CRUISE AT FL310, FO FLYING, AUTOPLT ON, LNAV ON, VNAV ON, FO IS BRIEFING ILS DME RWY 34L APCH TO SLC. WHEN FO NOTICES ACFT DSNDING VERY SLOWLY PASSING THROUGH FL306, FO IMMEDIATELY KICKED OFF AUTOPLT, HAND FLEW ACFT BACK TO FL310. TRIED 'A' AND 'B' AUTOPLTS, NO HELP. ACFT WAS TOO ERRATIC TO FLY IN PITCH SO HE HAND FLEW IT. LATER, DISCOVERED A FLT CTL 'SPD TRIM FAIL.' NO COMMENT WAS MADE TO US ABOUT ALTDEV. REST OF FLT UNEVENTFUL.
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.