Narrative:

Cruising at FL410 we became aware that air data computer 1 and air data computer 2 we're giving erroneous airspeed indications. After discussion with company and maintenance we decided air data computer 3 was providing accurate information. During descent in the mid 30's the yaw damp began applying left and right inputs causing oscillations and both engines went into altitude cont. We selected the yaw damp off causing the autopilot to disengage and the flight director cues disappeared. We tracked slightly off course and corrected back onto the arrival. We asked brasilia and rio control for relief from crossing restrictions and continued on the approval path to an uneventful landing.

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Original NASA ASRS Text

Title: Gulfstream Captain experiences the loss of ADC 1&2 in cruise at FL410. ADC 3 is determined to be reliable and the flight continues to destination.

Narrative: Cruising at FL410 we became aware that ADC 1 and ADC 2 we're giving erroneous airspeed indications. After discussion with company and maintenance we decided ADC 3 was providing accurate information. During descent in the mid 30's the yaw damp began applying left and right inputs causing oscillations and both engines went into ALT CONT. We selected the yaw damp off causing the autopilot to disengage and the flight director cues disappeared. We tracked slightly off course and corrected back onto the arrival. We asked Brasilia and Rio control for relief from crossing restrictions and continued on the approval path to an uneventful landing.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.