A plane that crashed in July 2013 and killed the pilot and two families heading from Soldotna to a remote Alaska lodge for bear viewing may have been overloaded and unbalanced, according to investigative documents released Wednesday by the National Transportation Safety Board.
The NTSB hasn't issued an official finding on what may have caused the crash, but as part of its investigation posted about 400 pages of key documents early Wednesday on its website. The records include descriptions of photos and an iPhone video shot by the passengers and used by the NTSB to recreate the failed takeoff.
The single-engine, turbine-powered de Havilland Otter was operated by Rediske Air Inc. in Nikiski as an on-demand charter.
A Rediske employee who answered the phone Wednesday at the Kenai Peninsula air taxi office said the company was still reviewing the documents. Rediske wasn't ready to comment, he said.
NTSB fact sheets released Wednesday gave slightly contradictory information on the plane's setup. The NTSB group investigating operations said the Otter was outfitted to carry nine passengers -- the number aboard the July 7, 2013, flight and the most that Rediske Air was authorized to fly. The group investigating "air worthiness" said it was set up for 10 passengers. At any rate, nine passengers and 42-year-old pilot Walter "Willie" Rediske were on board.
It had a maximum gross weight limit of 8,000 pounds counting the plane, fuel, cargo, baggage and occupants. For the flight from Soldotna, the NTSB estimated the weight ranged from 7,411 pounds to 8,038 pounds.
The plane may have been loaded tail heavy, an NTSB weight and balance study suggests. The center of gravity likely was several inches too far to the rear, or aft, of the plane, the investigation found. On takeoff, a center of gravity too far aft could have caused the nose to rise higher than usual and the aircraft to stall.
During takeoff, the Otter crashed and burned, making reconstruction of the accident complex.
The families killed were from Greenville, S.C., and included two couples and five children headed on a Sunday overnight trip to Bear Mountain Lodge, about 90 miles southwest of Soldotna. The passengers were Milton and Kimberly Antonakos and their three children and Dr. Chris McManus, his wife, Stacey, and their two children.
Rediske was an experienced airman from Nikiski, the son of the airline founder and its co-owner at the time of his death. Insurance records indicate that most of his recent flying time had been in other types of planes, not the Otter, the NTSB report said.
That day, Rediske had been scheduled to make a different trip in the DHC-3 Otter, but it was cancelled. The two families had been set up to fly in two of Rediske Air's smaller planes but the pilot then decided to use the Otter "so the group could all fly on one airplane."
Bear Mountain Lodge's operator asked Rediske Air to bring groceries and supplies and delivered the goods to the air charter's base in Nikiski. The lodge operator, who helped load the cargo, estimated the supplies weighed 300 pounds.
The cargo wasn't weighed, and the estimated weight was too low, the NTSB investigation found.
Using the lodge's receipt from the Three Bears store, the NTSB calculated that the food bought there would have weighed 386 pounds. And other items were not on the receipt including produce, bedding, wall art and a variety of meat products: hamburger, chicken, ribs, steaks and roasts. There also wasn't a record of how much fuel was on board, the NTSB found. Food and lodge supplies recovered after the crash weighed 613 pounds, according to an NTSB weight and balance study.
The Otter was not included in Rediske Air's weight and balance program detailing loading schedules, even though schedules were listed for five other planes, the NTSB determined. That was an oversight, investigators were told.
There's no requirement that a charter operator of a single-engine plane document weights of cargo, bags and passengers, but the operator still must comply with approved weight and loading limitations, the NTSB said.
Ultimately the pilot is responsible for ensuring a plane is not overloaded and that the bags and cargo are properly distributed, said Mark Madden, a professor of professional piloting at the University of Alaska Anchorage's Aviation Technology Division.
The NTSB created six scenarios to estimate the plane's weight and balance, two of which related to the short flight when the pilot flew the Otter from Nikiski to Soldotna and four that concerned the takeoff with the families on board. The NTSB determined where passengers were sitting and carry-ons were stowed with the aid of digital photos from the passengers' phone and camera.
Three of the four scenarios found that the plane's center of gravity was too far back, and two indicated the overall weight was too high.
Madden reviewed key parts of the NTSB investigative reports and said the extra weight of just 20 to 40 pounds wouldn't have mattered because planes are built to carry more than the maximum listed.
"There's a safety margin there," he said.
But based on the NTSB report, the Otter's center of gravity required a narrow range of just over 16 inches. It needed to be loaded very carefully to keep it correctly balanced, Madden said.
The NTSB determined that the center of gravity could have been off by about 4 inches to 6 inches. That's a difference of 23 to 36 percent from the center-of-gravity range, Madden calculated.
If the NTSB scenarios are correct, that variation is significant and would explain why the plane stalled, he said. There wouldn't be enough distance between the tail elevator – the moveable air foil – and the center of gravity, he said.
"Think of a teeter totter on a playground," Madden said. A kid far enough back on the board can balance a bigger kid. But if the distance is shortened, the little kid loses that advantage.
The NTSB hasn't said when it expects to conclude its investigation.