TBM 700/TBM 850
Flight Crew Commercial; Flight Crew Instrument
Flight Crew Last 90 Days 20; Flight Crew Total 1000; Flight Crew Type 700
Situational Awareness; Workload
Aircraft Equipment Problem Critical; Deviation - Altitude Overshoot; Deviation / Discrepancy - Procedural Clearance
Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Aircraft; Human Factors
On climb out in hard IMC/turbulence/rain I had a complete airspeed indicator failure on pilot side. I misdiagnosed this as a pitot failure (since glass instruments were still reporting altitude and the indication 'seemed to make sense' for stage of climb out) and began to operate off copilot airspeed but otherwise pilot side instruments for altitude and heading. Autopilot kicked off when airspeed on G600 failed. Unfortunately it was still reporting altitude and I believed what I saw. I leveled on heading 270 at indicated 5;000 feet and began to diagnose/debug. Checked pitot heat; checked power settings; etc. while hand-flying to maintain altitude [and] heading. High workload environment to say the least. After several other steps; I pulled the alternate static - immediately restored airspeed indicator on pilot side but; to my surprise; altitude also immediately wound up to approximately 7;500-8;000 feet. Apparently it was not a pitot tube problem but a static problem. I cross checked to GPS altitude and began correcting; while hand-flying and maintaining 270. ATC no doubt saw same as me - a near instantaneous altitude gain of 2;500-3;000 feet - and contacted me for an immediate course change to 360. I complied and we worked together to get back to assigned altitude.Learnings: Cross check constantly in IMC even when instruments seem to make sense but especially if one fails. Do not just cross check the failed instrument as there may be cascaded problems and the initial diagnosis may be incorrect.
TBM7 pilot reported an altitude deviation resulted from a pitot static system anomaly.