What happened
The DC9 departed during rain with a surface temperature of 39 degrees Fahrenheit. After reaching cruise altitude, the flight crew discovered that the elevator control was frozen and immobile. To maintain control of the aircraft, the pilot operated using primary and alternate trim. The crew performed a descent into warmer air, which allowed the elevator to thaw, subsequently regaining normal control.
The investigation
Post-flight inspections of the aircraft and its systems revealed no anomalies. However, the investigation noted that two other Midwest Express Airlines DC9 aircraft had previously experienced similar elevator control difficulties. In those instances, departures occurred in rain with surface temperatures of 46 degrees Fahrenheit and 39 degrees Fahrenheit. During one of those prior events, maintenance personnel identified ice accretions within the elevator control bay of the vertical stabilizer.