The National Transportation Safety Board preliminary report doesn't say what caused the Feb. 10 crash, but aviation expert Jerry Kidrick said the report's description of the helicopter's movements as recounted by witnesses indicates its tail rotor wasn't working properly to keep the helicopter from spinning.
"There's no reason for that aircraft to be spinning 360 to the left ... unless the tail rotor is not being effective," likely due to a mechanical problem or gusty wind conditions in the canyon, said Kidrick.
The Airbus EC130 B4 helicopter operated by Papillon Grand Canyon Helicopters crashed in a rocky wash while approaching landing pads at Quartermaster Canyon on tribal land outside Grand Canyon National Park after flying from Boulder City, Nevada.
A full NTSB report won't be done for more than a year.
According to the preliminary report, the helicopter slowed as it neared the landing area and turned to the left to face the pads.
"Subsequently, the helicopter made at least two 360-degree left turn revolutions as it descended into the wash below where it impacted terrain and a post-crash fire ensued," the preliminary report stated.
Based on that description, the pilot was no longer in control of the helicopter because the tail rotor wasn't preventing it from spinning.
A pilot without an effective tail rotor could try to fly a helicopter fast enough to skid the down the helicopter on a wide-open, flat area such as a runway, but the terrain inside the canyon wouldn't allow that kind of maneuver, he said. "There's no place to accelerate forward."
The preliminary report said a weather observation site 2 miles (3 kilometers) from the crash location had winds of 12 knots and gusts up to 19 knots.
The injured tourists and pilot remained in critical condition Wednesday at University Medical Center of Southern Nevada, said Scott Kerbs, a spokesman for the Las Vegas hospital.