Boeing 737-7H4 N469WN incident near Denver, Colorado

Probable cause

The snowplow operator’s incapacitation due to fatigue, which resulted in the snowplow contacting a parked airplane. Contributing to the incident was the company’s lack of a policy regarding employee fatigue.

NTSB analysis

The passengers and the flight crew were seated, and the ground crew was preparing to push the airplane away from the gate. The snowplow was conducting snow removal operations in clean-up mode. According to a witness, the snowplow was traveling eastbound behind the airplane and just north of the vehicle service road. The snowplow passed the airplane and then initiated a gradual turn to the right. The snowplow continued around 180 degrees and hit the airplane on the left side near the empennage.

The snowplow operator reported that he fell asleep while driving. The investigation revealed that the snowplow operator reported for his shift at 1730 the day before the incident and worked until 0200 the next morning. The snowplow operator slept in his supervisor’s vehicle, which was actively involved in the snow removal operations. At 0800, the snowplow operator resumed snow removal operations, and he had been working for about 6.5 hours when the incident occurred. The snowplow operator had an opportunity to sleep for 6 hours in his supervisor’s vehicle; however, since the vehicle was being operated, he probably did not get uninterrupted sleep and most likely got less than 6 hours of sleep. Although the investigation was unable to determine how long the snowplow operator had been awake on the day before the accident or how long he had slept in his supervisor’s vehicle, he was most likely fatigued. The company did not have, and was not required to have, guidance or a policy addressing fatigue management.

Text from the NTSB. Open the NTSB docket for CEN12IA123 for the full record.