WHITE PASS — The man who led the state’s effort this week to find a plane that crashed, killing 10 people with Snohomish County ties, doubts that ice on the wings caused the plane to fall from the sky.
Icing has been a problem for the Cessna 208 Grand Caravan, the type of plane involved in this crash, the deadliest in the nation this year.
However, there are other more typical explanations for crashes in mountainous areas, including powerful downdrafts, pilot disorientation caused by flying into a cloud or mechanical problems, said Tom Peterson, the state Department of Transportation’s aviation emergency service coordinator.
Specific conditions are required before a dangerous amount of ice can build up on a plane’s wings, and initial indications, Peterson said, are that those factors were not present before Sunday night’s crash near White Pass.
“I don’t think icing was an issue based on my assessment of the weather report,” Peterson said. “You have to have visible moisture in the air for icing to occur.”
There may have been some clouds and moisture in the mountains near where the accident occurred, but the plane appears to have encountered clear conditions on most of the flight, he said.
“I know we all want answers, but it takes time,” Peterson said, adding that it will be up to federal investigators to sort out what happened. “Trying to determine what happened is a complicated situation. It could be that we never know what happened.”
Sunday’s crash appears to be the deadliest so far this year in the U.S., according to federal crash data kept by the National Transportation Safety Board.
A team of NTSB investigators began poring over the crash site on Wednesday, looking for clues to explain why the Cessna 208 did not make it home.
The investigation is being led by NTSB senior investigator Howard Plagens, said Debra Eckrote, regional director for the federal agency that investigates plane crashes.
“Howard will prepare a preliminary report (on the accident) over the next four to five days,” she said. “He spent the day out there. There are no conclusions or anything drawn at this point.”
The Cessna 208 is considered by many a reliable workhorse, but it also has a history of problems flying in icy conditions.
The plane left Star, Idaho, near Boise, on its way to Shelton, in Mason County, on Sunday. It was ferrying the sky divers between Idaho and Washington.
Peterson, who also is a pilot, lives and works in Snohomish County. On Tuesday, he found himself trying to answer questions from the families and friends of the crash victims.
Some of what he shared with them was not completely in sync with early speculation about what caused the crash.
Peterson viewed the wreckage from the air, and said he believes that the plane did not break apart in the air before it started falling. All of the wreckage appears to be in one location, spread out over a patch of mountainside that is about 100 feet by 60 feet.
Although nobody knows exactly what happened, investigators already have great detail about the flight itself, including a radar track with about 2,000 different data points that trace the route it flew. The data show where the plane was and its elevation every six seconds.
“We had a radar data track from the point when this aircraft took off in Idaho to 200 meters from where the airplane was located,” he said. “That’s pretty good.”
Investigators fed that information into a computer program developed by the U.S. Air Force, which uses Google Earth’s three-dimensional topography program to prepare a simulation of the view from the plane’s cockpit, Peterson said.
That analysis helped focus the search and led investigators preliminarily to conclude the plane crashed straight into the ground, going about 70 mph.
The last radar data point has the plane flying at an altitude of 5,500 feet and descending rapidly. The wreckage was found on the mountainside at 4,300 feet.
Aside from the flight’s final seconds, the computer analysis and radar data suggest the journey appears to have been “pretty routine, normal-looking until it gets to the Cascade crest,” Peterson said. “The weather was nice to Yakima. The destination (in Shelton) was clear.”
The nearest weather station in the mountains, at Stampede Pass, showed some cloud cover Sunday. Peterson said it isn’t clear if there was enough moisture in those clouds to cause ice to build up on the plane’s wings.
The NTSB in 2006 issued a safety advisory suggesting the Cessna 208 may not perform well in weather conditions prone to wing icing.
Peterson said there didn’t appear to be enough time after leaving the good weather over Yakima for ice to have built up on the wings.
“That’s just conjecture on my part,” he said, adding, “The mountains tend to make their own weather” and sometimes ice can form quickly.
Since it debuted in 1985, the Cessna 208 has been involved in 110 accidents in the U.S. and 151 worldwide, according to NTSB records.
The plane is popular, with 1,600 worldwide altogether logging about 70,000 hours of flight time per month, said Doug Oliver, a spokesman for Cessna Aircraft Co., of Wichita, Kan.
“It’s in the air a lot,” Oliver said. “It has an excellent safety record.”
Reporter Lukas Velush: 425-339-3449 or lvelush@heraldnet.com.
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