About Corporate Airlines(American Connection) flight 5966

American Connection flight 5966 departed Saint Louis (STL) at 18:42 on a flight to Kirksville (IRK). When 23 minutes from Kirksville, the weather report included a 4 mile visibility in mist with an overcast ceiling at 300 feet. Kirksville does not have an ILS, but the crew decided to continue. A few minutes later the flight was cleared to descend from FL120 to 8000 feet in preparation for a localizer DME approach to runway 36. At 19:20 the weather report now indicated that the visibility had decreased to 3 miles. After reaching 8000 feet ARTCC cleared the crew further down to 3000 feet after which the captain briefed the approach. After receiving some vectors for runway 36 the captain levelled off at 3100 feet. At 19:30 the flight was 11 miles from the final approach fix (FAF) and the crew cleared for the approach. Flaps and landing gear were selected down and descent was started, tracking the localizer. At 19:36 the flight descended through 1450 feet. The GPWS sounded: "five hundred." When reaching the minimum descent altitude the GPWS sounded: "minimums, minimums", and the captain stated: "I can see the ground there." The first officer could not see the ground. Descent was continued and a few seconds later the captain reported having the approach lights in sight. The decision was made to continue the descent. The airplane suddenly contacted trees at an elevation of 996 feet msl. The aircraft crashed and caught fire.

Probably cause:

PROBABLE CAUSE: "The National Transportation Safety Board determines that the probable cause of the accident was the pilots? failure to follow established procedures and properly conduct a non-precision instrument approach at night in IMC, including their descent below the MDA before required visual cues were available (which continued un-moderated until the airplane struck the trees) and their failure to adhere to the established division of duties between the flying and non-flying (monitoring) pilot.
Contributing to the accident were the pilots? failure to make standard callouts and the current Federal Aviation Regulations that allow pilots to descend below the MDA into a region in which safe obstacle clearance is not assured based upon seeing only the airport approach lights. The pilots? failure to establish and maintain a professional demeanor during the flight and their fatigue likely contributed to their degraded performance. "