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Flight crew of an MD83 disconnected the autoplt when it inadvertently disengaged from altitude hold and climbed the aircraft from assigned. They then returned the aircraft to assigned altitude and advised ATC as to what happened.
| Attributes | |
| ACN | 427866 |
| Time | |
| Date | 199902 |
| Day | Tue |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : gve |
| State Reference | VA |
| Altitude | msl bound lower : 28000 msl bound upper : 28500 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Operator | common carrier : air carrier |
| Make Model Name | MD-83 |
| Navigation In Use | Other |
| Flight Phase | cruise other |
| Route In Use | enroute airway : zdc |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Experience | flight time last 90 days : 130 flight time total : 7500 flight time type : 100 |
| ASRS Report | 427866 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Experience | flight time last 90 days : 240 flight time total : 9000 flight time type : 300 |
| ASRS Report | 427360 |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude other anomaly other |
| Independent Detector | other flight crewa |
| Consequence | Other |
| Supplementary | |
| Air Traffic Incident | Pilot Deviation |
Narrative:
I was first officer and PF on this flight and had been cleared to FL280. The autoplt was engaged and was controling vertical flight during the climb and throughout the subsequent leveloff at the assigned cruise altitude. Both myself and the captain verified and verbalized 'altitude capture,' and 'altitude hold' on the FMA. A short while later the 'altitude' warning sounded in the cockpit. I was joined immediately on the controls by the captain whom advised ATC of the autoplt malfunction. We simultaneously disconnected the autoplt and hand flew the airplane in the descent back to the assigned altitude. The 'altitude' alert sounds at approximately 300 ft deviation from the assigned altitude. By the time we were able to disconnect the autoplt and arrest the climb manually, however, the airplane had climbed an additional 100-200 ft, resulting in a total altitude deviation of 400-500 ft. It is possible that I inadvertently disconnected the pitch function of the autoplt by touching the manual pitch trim button on the control wheel, although I have no recollection (or need) of doing so. Another possibility is that the airplane was out pitch trim limits about the lateral axis which could have caused the altitude hold function of the autoplt to disengage. The event remains a mystery to both the captain and myself.
Original NASA ASRS Text
Title: FLC OF AN MD83 DISCONNECTED THE AUTOPLT WHEN IT INADVERTENTLY DISENGAGED FROM ALT HOLD AND CLBED THE ACFT FROM ASSIGNED. THEY THEN RETURNED THE ACFT TO ASSIGNED ALT AND ADVISED ATC AS TO WHAT HAPPENED.
Narrative: I WAS FO AND PF ON THIS FLT AND HAD BEEN CLRED TO FL280. THE AUTOPLT WAS ENGAGED AND WAS CTLING VERT FLT DURING THE CLB AND THROUGHOUT THE SUBSEQUENT LEVELOFF AT THE ASSIGNED CRUISE ALT. BOTH MYSELF AND THE CAPT VERIFIED AND VERBALIZED 'ALT CAPTURE,' AND 'ALT HOLD' ON THE FMA. A SHORT WHILE LATER THE 'ALT' WARNING SOUNDED IN THE COCKPIT. I WAS JOINED IMMEDIATELY ON THE CTLS BY THE CAPT WHOM ADVISED ATC OF THE AUTOPLT MALFUNCTION. WE SIMULTANEOUSLY DISCONNECTED THE AUTOPLT AND HAND FLEW THE AIRPLANE IN THE DSCNT BACK TO THE ASSIGNED ALT. THE 'ALT' ALERT SOUNDS AT APPROX 300 FT DEV FROM THE ASSIGNED ALT. BY THE TIME WE WERE ABLE TO DISCONNECT THE AUTOPLT AND ARREST THE CLB MANUALLY, HOWEVER, THE AIRPLANE HAD CLBED AN ADDITIONAL 100-200 FT, RESULTING IN A TOTAL ALTDEV OF 400-500 FT. IT IS POSSIBLE THAT I INADVERTENTLY DISCONNECTED THE PITCH FUNCTION OF THE AUTOPLT BY TOUCHING THE MANUAL PITCH TRIM BUTTON ON THE CTL WHEEL, ALTHOUGH I HAVE NO RECOLLECTION (OR NEED) OF DOING SO. ANOTHER POSSIBILITY IS THAT THE AIRPLANE WAS OUT PITCH TRIM LIMITS ABOUT THE LATERAL AXIS WHICH COULD HAVE CAUSED THE ALT HOLD FUNCTION OF THE AUTOPLT TO DISENGAGE. THE EVENT REMAINS A MYSTERY TO BOTH THE CAPT AND MYSELF.
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.