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A lancair 4P in cruise at FL240 has autoplt induce pitch oscillations. On descending; autoplt exceeded 2500 FPM. Disconnected autoplt.
| Attributes | |
| ACN | 666488 |
| Time | |
| Date | 200507 |
| Place | |
| Locale Reference | navaid : zzz.vor |
| State Reference | US |
| Altitude | msl bound lower : 23000 msl bound upper : 24000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zzz.artcc |
| Operator | general aviation : personal |
| Make Model Name | Experimental |
| Operating Under FAR Part | Part 91 |
| Flight Phase | cruise : enroute altitude change cruise : level |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | other |
| Function | flight crew : single pilot |
| Qualification | pilot : instrument pilot : cfi pilot : commercial pilot : multi engine |
| Experience | flight time last 90 days : 62.5 flight time total : 9116 flight time type : 60 |
| ASRS Report | 666488 |
| Person 2 | |
| Affiliation | government : faa |
| Function | controller : radar |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : excursion from assigned altitude maintenance problem : improper maintenance maintenance problem : improper documentation non adherence : far non adherence : published procedure |
| Independent Detector | aircraft equipment other aircraft equipment : altimeter other flight crewa |
| Resolutory Action | aircraft : automation overrode flight crew flight crew : overcame equipment problem flight crew : returned to original clearance flight crew : returned to assigned altitude |
| Consequence | other |
| Factors | |
| Maintenance | contributing factor : manuals performance deficiency : installation performance deficiency : logbook entry performance deficiency : non compliance with legal requirements |
| Supplementary | |
| Problem Areas | Chart Or Publication Flight Crew Human Performance Aircraft |
| Primary Problem | Aircraft |
Narrative:
This is an experimental lancair 4P turbine pwred aircraft. The aircraft was built and test flown by myself. All testing throughout the 40 hours was done at 17500 ft and below. I filed an IFR flight plan to ZZZ1 en route to ZZZ at FL240. Reaching FL240; I found that the autoplt was very sensitive on pitch. As fuel was burning off; I had to every now and then disconnect the autoplt and retrim the elevator to stop pitch oscillations. About 150 NM from destination; I was cleared down to FL220. On selecting the autoplt to 1000 FPM descent; it exceeded 2500 FPM; my first reaction was to trim the elevator up. This reduced the rate of descent. With no warning; the elevator pitched up sharply. Immediately disengaged and pushed the elevator forward to stop the climb. At 305 KTS it climbed through FL230 before I could resume normal flight. I did not exceed FL240. The rest of the flight was normal with the autoplt disconnected. The return flight from ZZZ was done VFR at 17500 ft. After inspection; it was found that the servo fitted must be changed to a high torque servo. Furthermore; the attachment point which is located on the elevator push rod must be moved to the bell crank to stop flex. This action will be taken before any flts are resumed.
Original NASA ASRS Text
Title: A LANCAIR 4P IN CRUISE AT FL240 HAS AUTOPLT INDUCE PITCH OSCILLATIONS. ON DSNDING; AUTOPLT EXCEEDED 2500 FPM. DISCONNECTED AUTOPLT.
Narrative: THIS IS AN EXPERIMENTAL LANCAIR 4P TURBINE PWRED ACFT. THE ACFT WAS BUILT AND TEST FLOWN BY MYSELF. ALL TESTING THROUGHOUT THE 40 HRS WAS DONE AT 17500 FT AND BELOW. I FILED AN IFR FLT PLAN TO ZZZ1 ENRTE TO ZZZ AT FL240. REACHING FL240; I FOUND THAT THE AUTOPLT WAS VERY SENSITIVE ON PITCH. AS FUEL WAS BURNING OFF; I HAD TO EVERY NOW AND THEN DISCONNECT THE AUTOPLT AND RETRIM THE ELEVATOR TO STOP PITCH OSCILLATIONS. ABOUT 150 NM FROM DEST; I WAS CLRED DOWN TO FL220. ON SELECTING THE AUTOPLT TO 1000 FPM DSCNT; IT EXCEEDED 2500 FPM; MY FIRST REACTION WAS TO TRIM THE ELEVATOR UP. THIS REDUCED THE RATE OF DSCNT. WITH NO WARNING; THE ELEVATOR PITCHED UP SHARPLY. IMMEDIATELY DISENGAGED AND PUSHED THE ELEVATOR FORWARD TO STOP THE CLB. AT 305 KTS IT CLBED THROUGH FL230 BEFORE I COULD RESUME NORMAL FLT. I DID NOT EXCEED FL240. THE REST OF THE FLT WAS NORMAL WITH THE AUTOPLT DISCONNECTED. THE RETURN FLT FROM ZZZ WAS DONE VFR AT 17500 FT. AFTER INSPECTION; IT WAS FOUND THAT THE SERVO FITTED MUST BE CHANGED TO A HIGH TORQUE SERVO. FURTHERMORE; THE ATTACHMENT POINT WHICH IS LOCATED ON THE ELEVATOR PUSH ROD MUST BE MOVED TO THE BELL CRANK TO STOP FLEX. THIS ACTION WILL BE TAKEN BEFORE ANY FLTS ARE RESUMED.
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.