CHI01LA075

The helicopter was on the downwind leg of an approach to land at the pilot's private heliport. The pilot said, "I took off from my hangar on my farm at about 5:00 pm with 2 friends to just go for a flight local. After flying about 40 minutes in the area of my farm we started back home. The weather was perfect with hardly any wind under 5 knots out of [the] north. I started a southernly downwind to my landing pad. We had just got over a frozen lake in the downwind when without warning or any reason to believe anything was wrong, the helicopter drop[ped] straight down on the lake without me moving any flight controls." A postaccident examination of the helicopter was conducted. The helicopter came to rest about 300 feet from the initial impact point on the frozen lake. No anomalies were found with respect to the airframe that could be associated with a pre-impact condition. No anomalies were found with respect to the engine. The end of civil twilight occured at 1807 and the phase of the moon was a waxing crescent with 1% of the Moon's visible disk illuminated.

On January 25, 2001, at 1812 eastern standard time, an Enstrom 480 helicopter, N704G, piloted by a private pilot, was substantially damaged on impact with a frozen lake near Dryden, Michigan. The aircraft was on the downwind leg of an approach to land at the pilot's private heliport. The 14 CFR Part 91 flight was not on a flight plan. Visual meteorological conditions prevailed at the time of the accident. The pilot was seriously injured, and the two passengers received minor injuries. The flight originated from the pilots farm about 1700.

The pilot said in a written statement, "I took off from my hangar on my farm at about 5:00 pm with 2 friends to just go for a flight local. After flying about 40 minutes in the area of my farm we started back home. The weather was perfect with hardly any wind under 5 knots out of [the] north. I started a southernly downwind to my landing pad. We had just got over a frozen lake in the downwind when without warning or any reason to believe anything was wrong, the helicopter drop[ped] straight down on the lake without me moving any flight controls."

A postaccident examination of the helicopter was conducted. The helicopter came to rest on the frozen lake in an upright position with the landing gear collapsed. The helicopter came to rest about 300 feet from the initial impact point. All three main rotor blade spars remained attached to the rotor hub. The main rotor drive rotated freely. The main rotor pitch change links were all separated at the upper rod end. All of the breaks exhibited signatures consistent with overload failure. The control system was examined and the cyclic controls were found to be continuous from the cyclic sticks to the swashplate. The collective control was continuous from the collective sticks to the swashplate except for a rod end bearing at the collective torque tube bellcrank that had separated from the pushrod.

The separated collective system pushrod and rod end bearing were examined. The bearing assembly had failed in the threaded portion of the shank. The pushrod was found to have a bend with scuffing on the inside of the bend. A metallurgical examination of the failed portion of the rod end bearing revealed signatures consistent with mechanical overload due to a bending load.

No anomalies were found with respect to the airframe that could be associated with a pre-impact condition. No anomalies were found with respect to the engine.

According to the United States Naval Observatory internet site, the end of civil twilight occured at 1807 and the phase of the moon was a waxing crescent with 1% of the Moon's visible disk illuminated.