Aircraft Accident: Loss of Control During Instrument Approach (N9011Y)

Accident Overview and Fatalities The aircraft departed the airport with one dry air pump inoperative and the other pump reading low. Approximately 2.5 hours later, control of the aircraft was lost during an instrument approach in instrument meteorological conditions (IMC). The accident resulted in the deaths of both occupants on board. The final phase of the accident involved an uncontrolled descent and an in-flight collision with terrain or water. ## Mechanical Findings and Maintenance Issues Examination of the wreckage revealed that both pump driveshafts were sheared, and the broken shaft surfaces exhibited polished characteristics. Further testing indicated that tape or pipe dope had been used in the threading of the intake and outflow fittings of the left pump. While no contaminants were found in the right pump, the inner surface gap of the pump wall was measured at approximately 0.005 inch, a value roughly 50% over the allowable tolerance for a serviceable air pump. ## Instrumentation and Regulatory Findings The pressure regulator valve supplying the attitude indicator gyro and the compass gyro was examined and found to require pressure exceeding normal requirement standards. The official investigation identified multiple contributing factors, including a pneumatic system failure resulting in no pressure, the operation of the aircraft with known equipment deficiencies, and improper use of equipment by the pilot in command. Additional findings included a disabled attitude gyro, false indications from the attitude indicator, and improper maintenance installation by company maintenance personnel. The investigation also cited the pilot in command's psychological condition, pressure, improper judgment, failure to follow emergency procedures, improper use of procedures, and deficiencies in qualification and recent experience in type operation.