What was found
N885GM HAS ALTIMETRY SYSTEM ERROR (ASE) OF GREATER THAN 200 FEET ON THREE OCCASIONS WITH THE LATEST OF OCCURRING 12/10/2023. PART 91 OPERATOR HAS PREVIOUSLY ATTEMPTED REPAIRS; PITOT L/H HEAT RELAY REPLACED ON 09/12/2023 AND L/H UPPER AND R/H LOWER PROBES ON 10/13/2023. AS OF 12/20/2023 AIRCRAFT REMAINS RESTRICTED FROM OPERATING IN RVSM AIRSPACE PER 14 CFR 91 APPENDIX G SECTION 9 PARAGRAPH (B) BECAUSE ASE REMAINS GREATER THAN 200 FEET. ADDITIONAL REPAIRS PENDING.