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The reporter's autoplt trimmed nose up on the descent so that after leveling at the assigned altitude the aircraft popped back up 1000 ft when the autoplt was disconnected. Altitude deviation altitude excursion.
| Attributes | |
| ACN | 297571 |
| Time | |
| Date | 199502 |
| Day | Mon |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : cae |
| State Reference | SC |
| Altitude | msl bound lower : 29000 msl bound upper : 30000 |
| Environment | |
| Flight Conditions | Mixed |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : ztl |
| Operator | common carrier : air taxi |
| Make Model Name | Learjet 25 |
| Operating Under FAR Part | Part 91 |
| Flight Phase | descent other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | Other |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : instrument pilot : cfi pilot : atp |
| Experience | flight time last 90 days : 90 flight time total : 3080 flight time type : 975 |
| ASRS Report | 297571 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : commercial |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : clearance |
| Independent Detector | other flight crewa |
| Resolutory Action | flight crew : overcame equipment problem flight crew : returned to intended course or assigned course |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | other |
Narrative:
Same autoplt that was written up on an ASRS form dated feb/xx/95. Leveling off at FL290 using the autoplt pitch control, the PF trimmed nose up. After the input, he and I both noticed that the trim clicker was still autoplt activated. The aircraft had been trimmed to an attitude of more than 5 degrees nose up. The PF then tried to trim nose down in autoplt mode with no response. He then disconnected the autoplt and tried to trim nose down and after a few seconds that aircraft responded. By this time the aircraft had climbed to 1000 ft above our assigned altitude. We corrected to our assigned altitude and hand flew the aircraft the remainder of the trip. Once on the ground, I was able to duplicate the malfunction. The switch used for pitch trim in the autoplt will occasionally jam and will not disconnect even with the switch in the neutral or opposite position. Again, I believe the autoplt needs to be repaired or replaced and barring that, needs to be closely monitored. The only other option is not to use it. I believe the altitude deviation could have been limited if the autoplt had been more closely monitored and response had been faster on the controls. Callback conversation with reporter revealed the following information: the form was incomplete. The aircraft type was a lear 25 the reporter said. He could cause the sticking problem to occur on the ground but maintenance could not. Finally, after a couple of months the autoplt problem was addressed and corrected.
Original NASA ASRS Text
Title: THE RPTR'S AUTOPLT TRIMMED NOSE UP ON THE DSCNT SO THAT AFTER LEVELING AT THE ASSIGNED ALT THE ACFT POPPED BACK UP 1000 FT WHEN THE AUTOPLT WAS DISCONNECTED. ALTDEV ALT EXCURSION.
Narrative: SAME AUTOPLT THAT WAS WRITTEN UP ON AN ASRS FORM DATED FEB/XX/95. LEVELING OFF AT FL290 USING THE AUTOPLT PITCH CTL, THE PF TRIMMED NOSE UP. AFTER THE INPUT, HE AND I BOTH NOTICED THAT THE TRIM CLICKER WAS STILL AUTOPLT ACTIVATED. THE ACFT HAD BEEN TRIMMED TO AN ATTITUDE OF MORE THAN 5 DEGS NOSE UP. THE PF THEN TRIED TO TRIM NOSE DOWN IN AUTOPLT MODE WITH NO RESPONSE. HE THEN DISCONNECTED THE AUTOPLT AND TRIED TO TRIM NOSE DOWN AND AFTER A FEW SECONDS THAT ACFT RESPONDED. BY THIS TIME THE ACFT HAD CLBED TO 1000 FT ABOVE OUR ASSIGNED ALT. WE CORRECTED TO OUR ASSIGNED ALT AND HAND FLEW THE ACFT THE REMAINDER OF THE TRIP. ONCE ON THE GND, I WAS ABLE TO DUPLICATE THE MALFUNCTION. THE SWITCH USED FOR PITCH TRIM IN THE AUTOPLT WILL OCCASIONALLY JAM AND WILL NOT DISCONNECT EVEN WITH THE SWITCH IN THE NEUTRAL OR OPPOSITE POS. AGAIN, I BELIEVE THE AUTOPLT NEEDS TO BE REPAIRED OR REPLACED AND BARRING THAT, NEEDS TO BE CLOSELY MONITORED. THE ONLY OTHER OPTION IS NOT TO USE IT. I BELIEVE THE ALTDEV COULD HAVE BEEN LIMITED IF THE AUTOPLT HAD BEEN MORE CLOSELY MONITORED AND RESPONSE HAD BEEN FASTER ON THE CTLS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE FORM WAS INCOMPLETE. THE ACFT TYPE WAS A LEAR 25 THE RPTR SAID. HE COULD CAUSE THE STICKING PROB TO OCCUR ON THE GND BUT MAINT COULD NOT. FINALLY, AFTER A COUPLE OF MONTHS THE AUTOPLT PROB WAS ADDRESSED AND CORRECTED.
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.