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CE525 pilot experiences a sudden climb from FL430 with the autopilot engaged in altitude hold mode and with no audible warning. It is thought that inadvertent autopilot pitch trim activation may have caused the deviation.
| Attributes | |
| ACN | 932338 |
| Time | |
| Date | 201102 |
| Local Time Of Day | 1201-1800 |
| Place | |
| Locale Reference | ZZZ.ARTCC |
| State Reference | US |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Make Model Name | Citationjet (C525/C526) - CJ I / II / III / IV |
| Operating Under FAR Part | Part 91 |
| Flight Phase | Cruise |
| Route In Use | Direct |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Altitude Hold/Capture |
| Person 1 | |
| Function | Captain Pilot Flying |
| Qualification | Flight Crew Private Flight Crew Instrument Flight Crew Multiengine |
| Experience | Flight Crew Last 90 Days 37 Flight Crew Total 4796 Flight Crew Type 918 |
| Person 2 | |
| Function | Pilot Not Flying First Officer |
| Qualification | Flight Crew Commercial Flight Crew Instrument Flight Crew Multiengine |
| Experience | Flight Crew Last 90 Days 80 Flight Crew Total 19160 Flight Crew Type 1855 |
| Events | |
| Anomaly | Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance |
Narrative:
[We were] cruising at FL430 for 17 minutes. Autopilot in altitude hold mode. Suddenly it was noticed that aircraft started climbing without any audio warning in spite of altitude hold mode. Climb rate swiftly increased to 900 FPM. Immediately took corrective action to hand correct back to FL430. Altitude deviation was estimated to be some 1;500 ft. Only after descent corrective action in place ATC inquired for cause.both pilots immediately analyzed what could have caused the deviation (equipment malfunction or other). It was concluded that one possible cause could be that an inadvertent touching of the autopilot pitch trim wheel (on center pedestal left side) might have been of influence. When PIC turns or moves sideways his/her hip can come in contact with the pitch trim thumb wheel. The collins proline 21 autopilot's pitch trim wheel has no protection to the side like for instance many king airs have with a little 'fence' around the center console.corrective action: a) CJ2 OM (operating manual; page 2-73) states (if voice annunciator system is installed; which is the case in this aircraft) 'altitude' callout will be heard if the airplane deviates over 300 ft from the selected altitude. The manual does not indicate more specifically the alarm condition and altitude deviation; whether by turbulence or a deviation by pitch wheel. Immediate after landing contact with cessna service center revealed that there seems to be no altitude deviation audio alarm by this collins system for this case.b) contact with the collins representative revealed that there is an audio alarm for an altitude deviation of over 300 ft with altitude hold engaged. But duplication of the situation later in the flight when ATC cleared us to FL450 gave no alarm.c) an improvement would be possible with a mechanical 'protection' to avoid inadvertent thumb wheel contact. Cessna has been contacted to see if such a modification is available. A date is now set to bring the aircraft to the cessna service center to see if such a solution can be found.
Original NASA ASRS Text
Title: CE525 pilot experiences a sudden climb from FL430 with the autopilot engaged in altitude hold mode and with no audible warning. It is thought that inadvertent autopilot pitch trim activation may have caused the deviation.
Narrative: [We were] cruising at FL430 for 17 minutes. Autopilot in altitude hold mode. Suddenly it was noticed that aircraft started climbing without any audio warning in spite of altitude hold mode. Climb rate swiftly increased to 900 FPM. Immediately took corrective action to hand correct back to FL430. Altitude deviation was estimated to be some 1;500 FT. Only after descent corrective action in place ATC inquired for cause.Both pilots immediately analyzed what could have caused the deviation (equipment malfunction or other). It was concluded that one possible cause could be that an inadvertent touching of the autopilot pitch trim wheel (on center pedestal left side) might have been of influence. When PIC turns or moves sideways his/her hip can come in contact with the pitch trim thumb wheel. The Collins Proline 21 autopilot's pitch trim wheel has no protection to the side like for instance many King Airs have with a little 'fence' around the center console.Corrective Action: a) CJ2 OM (Operating Manual; page 2-73) states (if voice annunciator system is installed; which is the case in this aircraft) 'ALTITUDE' callout will be heard if the airplane deviates over 300 FT from the selected altitude. The manual does not indicate more specifically the alarm condition and altitude deviation; whether by turbulence or a deviation by pitch wheel. Immediate after landing contact with Cessna Service Center revealed that there seems to be no altitude deviation audio alarm by this Collins system for this case.b) Contact with the Collins representative revealed that THERE IS AN AUDIO ALARM FOR AN ALTITUDE DEVIATION OF OVER 300 FT WITH ALTITUDE HOLD ENGAGED. But duplication of the situation later in the flight when ATC cleared us to FL450 gave no alarm.c) An improvement would be possible with a mechanical 'protection' to avoid inadvertent thumb wheel contact. Cessna has been contacted to see if such a modification is available. A date is now set to bring the aircraft to the Cessna Service Center to see if such a solution can be found.
Data retrieved from NASA's ASRS site as of April 2012 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.