A lj-35 mach trim computer malfunctioned in flight preventing the aircraft from being trimmed at FL2...

Attributes
ACN	968013
Time
Date	201109
Local Time Of Day	1801-2400
Place
Locale Reference	ZZZ.ARTCC
State Reference	US
Environment
Light	Night
Aircraft 1
Make Model Name	Learjet 35
Operating Under FAR Part	Part 135
Flight Phase	Climb
Route In Use	Direct
Flight Plan	IFR
Component
Aircraft Component	Mach Trim
Person 1
Function	Captain Pilot Flying
Qualification	Flight Crew Air Transport Pilot (ATP) Flight Crew Flight Instructor Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 70 Flight Crew Total 10625 Flight Crew Type 3070
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance

Narrative:

We had climbed to fl 260 and were in the process of leveling off at our assigned altitude of fl 270. The first officer was hand-flying the aircraft. As he started his level-off he indicated he was encountering trim problems with the aircraft. I took the controls and attempted to level the aircraft and also experienced the feeling that the trim was not responding correctly to inputs. I reduced power and as the aircraft slowed I was able to regain positive pitch control but during the process we deviated above and below the assigned altitude. We also got a mach trim warning. We radioed center and informed them of the problem and asked them if they had had any reports of wave action (we were experiencing moderate chop during the level off) and they responded negatively. We then requested a descent to fl 230. I told the first officer to engage the autopilot and we descended to the requested/assigned altitude of fl 230. With the auto pilot engaged we continued the flight with no additional problems. I discussed the problem with our maintenance department and they feel it is a problem starting with the mach trim computer and they will be checking it and making any needed repairs.

Original NASA ASRS Text

Title: A LJ-35 Mach Trim Computer malfunctioned in flight preventing the aircraft from being trimmed at FL260 but normal operation returned after descending to FL230.

Narrative: We had climbed to FL 260 and were in the process of leveling off at our assigned altitude of FL 270. The First Officer was hand-flying the aircraft. As he started his level-off he indicated he was encountering trim problems with the aircraft. I took the controls and attempted to level the aircraft and also experienced the feeling that the trim was not responding correctly to inputs. I reduced power and as the aircraft slowed I was able to regain positive pitch control but during the process we deviated above and below the assigned altitude. We also got a Mach Trim warning. We radioed Center and informed them of the problem and asked them if they had had any reports of wave action (we were experiencing moderate chop during the level off) and they responded negatively. We then requested a descent to FL 230. I told the First Officer to engage the autopilot and we descended to the requested/assigned altitude of FL 230. With the auto pilot engaged we continued the flight with no additional problems. I discussed the problem with our maintenance department and they feel it is a problem starting with the Mach trim computer and they will be checking it and making any needed repairs.

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.

A lj-35 mach trim computer malfunctioned in flight preventing the aircraft from being trimmed at FL260 but normal operation returned after descending to FL230.