MU-2
Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 20; Flight Crew Total 11000; Flight Crew Type 3000
Human-Machine Interface; Training / Qualification
Deviation - Altitude Overshoot; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Unstabilized Approach
Air Traffic Control Issued Advisory / Alert; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft; Human Factors
Descending into the airport I flew through my assigned altitude of 3;000 feet by approx. 150 feet.  I caught it at the same time approach called us to check our altitude.  The altitude captured on the autopilot but due to the descent rate it flew through the selected altitude. This day was our first working trip with a newly installed glass panel GTN 750 and G600.  We had read the books and trained on the simulator program for weeks but we both were way behind the aircraft on the approach. We had even made a training flight previously and completed both ILS and GPS approaches successfully.  The workload became high when the copilot tried to reload the approach to get it to activate properly and he lost an intermediate fix. While I attempted to assist in reestablishing the approach I let my airspeed drop below what had been assigned by ATC.  As soon as I saw the airspeed deviation I corrected it. I considered just going around and getting set up again when we saw the field and could continue visually.  More training in the actual aircraft prior to working trips should have been conducted.
Twin turboprop Captain reports being unprepared for his first flight after the aircraft had been equipped with newly installed glass panel GTN 750 and G600 flight displays. Although simulator training and actual training flight had occurred; the crew was not prepared for the real thing.