Flight Briefing and Departure
The pilot of helicopter N2005A stated that before departing from Oklahoma City, Oklahoma, he contacted the Oklahoma City Flight Service Station (FSS) and obtained a weather briefing. The briefing indicated light rain showers, a minimum ceiling of 1,800 feet, visibility of 3 to 5 miles, and no chance of fog except in low-lying areas.
Mission and Diversion
The pilot and another pilot departed in a flight of two helicopters to transport a patient from Ardmore, Oklahoma, to Oklahoma City. After arriving at Ardmore, the mission was canceled because the patient died.
Return Flight and Weather Deterioration
Approximately 1 hour and 20 minutes after arriving at Ardmore, the two helicopters departed for the return flight after receiving the Ardmore ATIS. The other helicopter was equipped with a radar altimeter and led the way over mountainous terrain. The pilot of N2005A was following about 3/4 mile behind when the ceiling and visibility deteriorated to about 500 feet and 1 mile.
Collision with Terrain
The pilot stated that he had closed on the lead helicopter and was descending and decelerating when his aircraft collided with the ground. The impact occurred on banked terrain beside a highway.