Flight Overview
A cargo flight was scheduled to pick up cargo at the destination airport and then deliver it to another location. During the descent, 14 minutes before the accident, the airplane entered a layer of moderate rime ice. The captain, who was the pilot flying, and the first officer, the monitoring pilot, made multiple statements indicating their awareness of airframe icing.
Approach and Control Issues
After reaching visual flight rules (VFR) conditions, the flight crew canceled the instrument flight rules (IFR) clearance and initiated a right, circling approach to the runway. While turning onto the base leg of the traffic pattern, 45 seconds prior to the accident, the captain called for full flaps. The engine power levers were adjusted several times between 50 and 95 percent. The captain also inquired about the autopilot and fuel balance. The first officer responded that he did not think the spoilerons were working. Shortly thereafter, the first officer commanded full engine power, and the airplane impacted terrain.
Cockpit Environment
Cockpit voice recorder data revealed multiple instances during the flight, while below 10,000 feet mean sea level, where the crew engaged in discussions inconsistent with a sterile cockpit environment. For example, a lengthy discussion about Class B airspeeds occurred, which may have contributed to a relaxed and casual cockpit atmosphere. The flight crew appeared to conduct checklists in a generally informal manner. As this was a Part 135 operation, both pilots were expected to be versed in sterile cockpit rules and adherence to procedures, including checklist discipline.
Final Moments
For approximately the last 24 seconds of flight, both pilots were likely focusing on identifying and understanding the reason for the airplane's roll handling difficulties, as noted by the captain's comment about fuel balance. These events, culminating in the first officer's urgent command to add full power, suggested that neither pilot detected the airplane's decaying energy state before it reached a critical level for the conditions encountered.
Investigation Findings
Light bulb filament examination revealed that the aileron augmentation system and stall warning lights illuminated in the cockpit. No mechanical anomalies were found to substantiate a failure in the aileron augmentation system. No additional mechanical or system anomalies were noted with the airplane. A performance study, limited by available data, could not confirm the airplane's movements relative to an aileron augmentation system or spoileron problem. The level of airframe icing and its possible effect on the airplane at the time of the accident could not be determined. There was no evidence of flight crew impairment or fatigue in the final 30 minutes of the flight.