Date: 202105
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: Mixed
Weather elements / visibility: Rain; Thunderstorm; Turbulence; 3
Light: Daylight
Aircraft: TBM 700/TBM 850
Operator: Personal
Operating under: Part 91
Flight plan: IFR
Mission: Personal
Flight phase: Final Approach
Airspace: Class D ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Autopilot
Component problem: Malfunctioning
Reporter organization: Personal
Reporter function: Captain; Single Pilot
Reporter qualification: Flight Crew Commercial; Flight Crew Instrument
Human factors: Confusion; Distraction; Situational Awareness
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Altitude Overshoot; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; General Maintenance Action
Contributing factors: Human Factors; Aircraft
Primary problem: Aircraft

Narrative: This was not a good flight because of compounding errors that happened and the negative effect that they had.  The good part is that the flight remained safe; but here below are several things that I learned.  The events started when on decent into ZZZ when the lights on the autopilot mode selector began to flicker erratically; however the autopilot appeared to perform normally.  This was in IMC descent thru layers with occasional moderate turbulence.  (The was second flight after the power supply to the EFIS system failed resulting in loss of the primary attitude indicator and HSI which was repaired and return to service.  I mention this only because it attributed to my increase lack of trust in the flight instruments.) The autopilot was on altitude preselect with a vertical speed selected.  During the decent I was evaluating the autopilot issue and I think; after the fact; I pushed the altitude capture twice; resulting in me disengaging the capture and descending below the desired altitude.  At the time I attributed this to a malfunction autopilot and I decided to disconnect the autopilot and manually flew the plane.  This increased the workload.  Weather was also a significant factor.  There was a line of thunderstorms that were moving over ZZZ (destination) and I was watching the satellite radar utilizing a portable GDL52 communicating to Garmin pilot on my I pad. For this flight I was using ForeFlight for navigation/charts and Garmin Pilot for weather; because the GDL would not communicate satellite radar information to ForeFlight.  I have been using ForeFlight for charts and weather in previous aircraft for many years; but this aircraft has only ADSB-out and is scheduled to have an avionics upgrade to a GDL69a (sat WX) and Garmin 345 (ADSB IN/Out) installation in Month.  I was also utilizing the onboard radar; but am learning to use this system.  Bottom line was too many nav / weather systems in use that resulted in unnecessary and additional workload. Another factor was that I had transitioned from a piston to a turboprop and had about 80 hours in the TBM time at the time of this flight. So I was still low on the TBM experience curve.   Based on the weather I requested GPS XX and activated the approach on the 530s. However; as I proceeded to ZZZ GPS XX; the weather changed and the IAF for GPS XX was near the line of thunderstorms and center offered ILS XY and left turn to heading for the IAF - I made a right turn to that heading.  I should have recognized that I was starting to make small mistakes. During this time I also was varying from assigned altitude due to increase workload.   I entered ILS XX in to the 530S and activated and Center vectored me to the approach.   I began the approach and was able to see the ground occasionally.  I was handed off the Tower and I waited to capture the glideslope. I continued the approach; my position and altitude were not cross checking; and I began try to determine why.  I was high when I was on a 2-3 mile final.  While making this evaluation; I was able to see the runway lights and able to make a visual decent and landing.  I was not confident after this flight; there were too many mistakes in this flight.  When I was on the ground I contacted my flight instructor and went over flight and discussed the avionics and my reaction/ decision I made.  We made a plan of how to determine the effect of the flickering light on the mode selector and insure that it was safe for flight.  I altered my plans so that weather would have a minimal impact and returned back to ZZZ1.  To learn and avoid these errors in the future; I did a full debrief with my instructor when I return home.  This focused on both the avionics and cross reference that he recommended to determine status of the navigation system.  We also spent a considerable time on how I responded to the apparent situation and decision making.  It was at this time; I realized how much some minor errors in my part had a large impact onthe flight.  The avionics have also been evaluated by Company in ZZZ2 and determine that the malfunction was limited to the mode selector display and that the autopilot is functioning normally. It is schedule to be repaired.   Further I have also flow approaches in VFR conditions to verify operations of the navigation and autopilot systems and apply some of the procedures that my instructor and I discussed.




Synopsis: Pilot reported autopilot system failure caused difficulties on approach and landing.