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Flight crew of a gulfstream III G3 descended off of cruise altitude due to the autoplt inadvertently disengaging from altitude capture mode.
| Attributes | |
| ACN | 420830 |
| Time | |
| Date | 199811 |
| Day | Sun |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : ilm |
| State Reference | NC |
| Altitude | msl bound lower : 40700 msl bound upper : 41000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Dusk |
| Aircraft 1 | |
| Controlling Facilities | artcc : zdc |
| Operator | general aviation : corporate |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | Other |
| Flight Phase | cruise other |
| Route In Use | enroute airway : zdc |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | Other |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : commercial pilot : cfi pilot : atp |
| Experience | flight time last 90 days : 150 flight time total : 11500 flight time type : 600 |
| ASRS Report | 420830 |
| Person 2 | |
| Affiliation | Other |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other |
| Independent Detector | other flight crewa |
| Resolutory Action | flight crew : returned to intended course or assigned course |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
Aircraft was in light to moderate chop. Pilot was changing between heading and long range navigation modes on FMS. At some point (not noticed by either of us) the altitude hold mode disengaged allowing aircraft to descend 300 ft below altitude. Pilot immediately corrected to altitude.
Original NASA ASRS Text
Title: FLC OF A GULFSTREAM III G3 DSNDED OFF OF CRUISE ALT DUE TO THE AUTOPLT INADVERTENTLY DISENGAGING FROM ALT CAPTURE MODE.
Narrative: ACFT WAS IN LIGHT TO MODERATE CHOP. PLT WAS CHANGING BTWN HDG AND LONG RANGE NAV MODES ON FMS. AT SOME POINT (NOT NOTICED BY EITHER OF US) THE ALT HOLD MODE DISENGAGED ALLOWING ACFT TO DSND 300 FT BELOW ALT. PLT IMMEDIATELY CORRECTED TO ALT.
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.