Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Commercial; Flight Crew Multiengine
Flight Crew Last 90 Days 40; Flight Crew Total 7100; Flight Crew Type 700
Aircraft Equipment Problem Less Severe; Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Maintenance; Deviation / Discrepancy - Procedural Published Material / Policy
Aircraft
Straight & level at 17;000 [feet]; IMC on autopilot in NAV/ALT mode; light-mod turbulence. In mod turbulence with updraft; autopilot failed and disconnected; aircraft climbed approx 400 feet.  ATC noted altitude change; provided altitude readout and altimeter setting; we responded that autopilot failed in turbulence and correcting. Autopilot was reset and performed normally for the remainder of the flight. The autopilot has had similar failures over the past few weeks; all reported to Chief Pilot and [Maintenance/Management]. He responded on most reports that 'we'll get someone to look at it' but crew was not informed if any maintenance checks; and scheduled flights continued despite reports.  After the above instance was reported with mention of ATC comment; maintenance was scheduled and 3 more legs were flown before delivering the aircraft to the shop on the evening of DATE. I am concerned that [Maintenance/Management] is reluctant to take the aircraft out of service for pilot squawks. We have had previous conversations where our ability to recognise situations indicating a need for maintenance  were questioned; we were threatened for 'challenging' him; advised that he had hired us and he could fire us.
PC-12 flight crew reported the aircraft autopilot malfunctioned. They reported encountering resistance from Management to address maintenance issues.