Helicopter Water Impact in the Gulf of Mexico (N5829D)

Incident Overview and Environmental Conditions During an offshore flight in the Gulf of Mexico, approximately 3 nautical miles from San Luis Pass, a helicopter encountered low ceilings and low visibilities. The pilot began to slow the aircraft and descended to approximately 50 feet above the water. He initiated a right turn to reverse direction while continuing to reduce speed. During the turn, the aircraft began to vibrate, which the pilot recognized as the transverse flow effect. Due to the lack of visual resolution of the water surface, the pilot had difficulty determining his exact altitude. He immediately applied collective and forward left cyclic to level the aircraft. The vibrations accelerated, and the aircraft began an uncommanded turn to the right. The pilot followed the turn with cyclic and allowed the aircraft to descend. He rolled off the throttle, and the spin stopped. Before the pilot could inflate the floats, the helicopter impacted the water, rolled over onto its right side, and subsequently sank. The raft was recovered from the helicopter, and the pilot and passengers floated in dense fog for about 3 1/2 hours before washing ashore at Surfside Beach.