A rapid change in weather over Silverton early on the afternoon of Dec. 3, 2011, likely contributed to the crash of a small passenger plane that left four Durango residents dead, according to a report by the National Transportation Safety Board.
Also, the NTSB said the pilot of the doomed plane pleaded for help from an air-traffic controller moments before the plane disappeared from radar and contact was lost.
What the NTSB calls a factual report was issued March 20 by the agency, noting the plane left Animas Air Park in Durango at 1:19 p.m., without filing a flight plan.
The NTSB stated instrument meteorological conditions limited visibility because of weather prevailed at the time, but the pilot, Steve Osborne, 59, was not rated to fly a plane using only instruments for navigation.
Osborne and his three passengers were killed. The passengers were Steve Osbornes wife, Jan Measles Osborne, 50; Tyler Black, 24; and Gena Rych, 27. They were en route from Durango to Aspen to attend a party for Alpine Bank.
According to a weather study conducted by an NTSB meteorologist, at noon Dec. 3, cloud tops in the San Juan Mountains were at about 13,000 feet, but by 2 p.m., a low-pressure system and a surface trough had pushed clouds as high as 22,000 feet.
The plane crashed about 1:35 p.m., in Soda Gulch just north of Silverton. Small bits of debris rained down on County Road 110 north of town, and the crash left a debris field 200 feet wide and 1,200 feet long.
The wreckage was recovered last spring and reassembled in a hangar in Greeley.
The NTSB reported the pilot contacted air-traffic control in Denver just before the crash, stating he was 12 miles southeast of Telluride (almost over Silverton) at an altitude of about 20,000 feet.
The pilot requested visual flight rules flight following (navigational assistance) to (Aspen airport) and reported that he could not descend below his altitude and maintain visual flight rules, the NTSB report stated.
Denver Center reminded the pilot that in order to fly VFR, he needed to be below the flight levels (below 18,000 feet). The pilot reported that he would descend below the flight levels as soon as he could. Denver Center asked the pilot if he could maintain VFR below his current altitude, and the pilot responded that he could not.
The air-traffic controller then asked Osborne if he was capable of instrument-only flight.
Im capable. Im studying it at this time, but if you could help me head on over, Id sure appreciate it, Osborne said, according to the report.
The NTSB said Denver Center asked the pilot if he was capable and qualified for instrument flight, and the pilot replied that he was not qualified.
That was the last radio communication from the pilot, the NTSB report states.
Moments later, the airplane disappeared from radar and contact with the pilot was lost, the NTSB report says.
The NTSB said witnesses in the Silverton area heard the plane overhead, but they did not see it through the clouds, and it sounded as if it were doing aerobatics or changing elevation quickly.
Last weeks report by the NTSB is not the final verdict about the crash. The NTSBs final report is pending; it is likely to be released within the next six months.
While the report did not list an exact cause of the crash, it pointed to the weather conditions and noted studies showing that a pilot who has not been trained in attitude instrument flying, or whose instrument skills have eroded, will lose control of the airplane in about 10 minutes once forced to rely solely on instrument reference.
The report stated Osborne had about 593 hours of flight time, including 217 hours in the plane that crashed, a Socata TB21 four-passenger, single-prop plane. But Osborne lacked instrument training.
The NTSB said if the natural horizon were to suddenly disappear, the untrained instrument pilot would be subject to vertigo, spatial disorientation and inevitable control loss.
The NTSB pointed out that it recommended in 2005 that private pilots be required to demonstrate basic ability with instrument control in the biennial flight reviews, but that recommendation has not been implemented.