SA-227 AC Metro III
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 100; Flight Crew Total 1970; Flight Crew Type 85
Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem; General Maintenance Action
Aircraft; Human Factors; Weather
Aircraft was leveled off at 11;000 when ATC queried me to say altitude. I responded level 11;000. He suggested I check altimeter setting at which time I noted the co-pilot altimeter was 400 feet higher on the same setting. I started a descent and switched to the Alternate static source which caused the pilot side altimeter to rise roughly 500 feet from where it was. I continued the flight and queried ATC about what altitude they showed me at to make sure all systems were now in agreement. Additionally with the autopilot on in level flight (no change in altitude by either altimeter); the pilot side VSI was steady at 400 fpm descent and the co-pilot VSI showed a 300 fpm climb. After landing the altimeters were accurate and the pilot side VSI showed a 200 fpm climb and the co-pilot vsi was level. I consulted the lead mechanic from base and he said to put the aircraft in a heated hangar where ice could melt and drain. The subsequent flight showed no irregularity after checking the normal and alternate sources. Contributing factors may have been de-icing fluid could have been sprayed into the static ports; or ice blockages/frost buildup in the static lines causing errors. The aircraft was left outside the night before in subzero temperatures and snow. The aircraft was also de-iced just before departure.
SA227 Captain experiences static system anomalies after the aircraft is left out overnight in extreme cold conditions and deiced just prior to departure. In flight ATC questions the reporters' altitude and the Captain discovers his altimeter reads 500 feet lower than actual. Switching to the alternate static source corrects the altimeter error but both VSI's are in error.