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B757. Altitude deviation caused by suspected temporary false information from air data computer to the autoplt at level cruise altitude.
| Attributes | |
| ACN | 490111 |
| Time | |
| Date | 200011 |
| Day | Wed |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | navaid : fak.vortac |
| State Reference | VA |
| Altitude | msl bound lower : 40650 msl bound upper : 10000 |
| Environment | |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zdc.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | B757 Undifferentiated or Other Model |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| ASRS Report | 490111 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : commercial pilot : instrument pilot : multi engine |
| ASRS Report | 490110 |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance |
| Independent Detector | other flight crewa other flight crewb |
| Resolutory Action | controller : issued advisory flight crew : returned to assigned altitude |
| Consequence | other |
| Supplementary | |
| Problem Areas | Aircraft |
| Primary Problem | Aircraft |
Narrative:
At FL410 level with left autoplt engaged, the captain's vsi indicated an approximately 500 FPM route of climb. As a result the l-hand autoplt commanded a descent of approximately 500 FPM, even though the captain's altimeter was showing level flight. The l-hand autoplt was disengaged. However, by that time an altitude deviation of 200-300 ft had occurred. Washington questioned our altitude. We indicated to them we possibly experienced an air data computer failure. The flight continued at FL410 without further incidence.
Original NASA ASRS Text
Title: B757. ALTDEV CAUSED BY SUSPECTED TEMPORARY FALSE INFO FROM AIR DATA COMPUTER TO THE AUTOPLT AT LEVEL CRUISE ALT.
Narrative: AT FL410 LEVEL WITH L AUTOPLT ENGAGED, THE CAPT'S VSI INDICATED AN APPROX 500 FPM RTE OF CLB. AS A RESULT THE L-HAND AUTOPLT COMMANDED A DSCNT OF APPROX 500 FPM, EVEN THOUGH THE CAPT'S ALTIMETER WAS SHOWING LEVEL FLT. THE L-HAND AUTOPLT WAS DISENGAGED. HOWEVER, BY THAT TIME AN ALTDEV OF 200-300 FT HAD OCCURRED. WASHINGTON QUESTIONED OUR ALT. WE INDICATED TO THEM WE POSSIBLY EXPERIENCED AN ADC FAILURE. THE FLT CONTINUED AT FL410 WITHOUT FURTHER INCIDENCE.
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.