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An MD80 in cruise flight at FL330 experienced an uncommanded autoplt disconnect; resulting in an altitude excursion of approximately 300 ft; and a turn off course.
| Attributes | |
| ACN | 700587 |
| Time | |
| Date | 200606 |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | navaid : ilc.vortac |
| State Reference | NV |
| Altitude | msl single value : 33000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Dawn |
| Aircraft 1 | |
| Controlling Facilities | artcc : zlc.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | MD-83 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| ASRS Report | 700587 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| ASRS Report | 700588 |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude non adherence : clearance other spatial deviation |
| Independent Detector | other controllerb other flight crewa other flight crewb |
| Resolutory Action | flight crew : returned to intended or assigned course flight crew : returned to original clearance flight crew : returned to assigned altitude |
| Consequence | other |
| Supplementary | |
| Problem Areas | Aircraft |
| Primary Problem | Aircraft |
Narrative:
During cruise portion of flight; autoplt entered a right descending turn and disconnected. I was placing my sfo charts away when the first officer noticed the red autoplt light. Once we confirmed that the autoplt was indeed off; and verified we were in an uncommanded descending r-hand turn; we attempted to smoothly transition back on course and altitude. In transitioning back to our filed altitude; we deviated approximately 250-300 ft. We wrote up the autoplt; and notified center. There was light mountain wave in our area; and the aircraft had flown through 2 small areas of it prior to the incident. We both feel that the amount of mountain wave activity was nowhere near enough to cause the autoplt to disconnect. Supplemental information from acn 700588: maintenance took the autoplt #1 OTS.
Original NASA ASRS Text
Title: AN MD80 IN CRUISE FLT AT FL330 EXPERIENCED AN UNCOMMANDED AUTOPLT DISCONNECT; RESULTING IN AN ALT EXCURSION OF APPROX 300 FT; AND A TURN OFF COURSE.
Narrative: DURING CRUISE PORTION OF FLT; AUTOPLT ENTERED A R DSNDING TURN AND DISCONNECTED. I WAS PLACING MY SFO CHARTS AWAY WHEN THE FO NOTICED THE RED AUTOPLT LIGHT. ONCE WE CONFIRMED THAT THE AUTOPLT WAS INDEED OFF; AND VERIFIED WE WERE IN AN UNCOMMANDED DSNDING R-HAND TURN; WE ATTEMPTED TO SMOOTHLY TRANSITION BACK ON COURSE AND ALT. IN TRANSITIONING BACK TO OUR FILED ALT; WE DEVIATED APPROX 250-300 FT. WE WROTE UP THE AUTOPLT; AND NOTIFIED CTR. THERE WAS LIGHT MOUNTAIN WAVE IN OUR AREA; AND THE ACFT HAD FLOWN THROUGH 2 SMALL AREAS OF IT PRIOR TO THE INCIDENT. WE BOTH FEEL THAT THE AMOUNT OF MOUNTAIN WAVE ACTIVITY WAS NOWHERE NEAR ENOUGH TO CAUSE THE AUTOPLT TO DISCONNECT. SUPPLEMENTAL INFO FROM ACN 700588: MAINT TOOK THE AUTOPLT #1 OTS.
Data retrieved from NASA's ASRS site as of January 2009 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.