Two witnesses saw a firefighting airplane that crashed while responding to a wildfire near Estes Park last month roll upside down before slamming into wooded terrain, according to a preliminary report released Wednesday by the National Safety Transportation Board.
One witness told federal air crash investigators that the plane’s pilot, Marc Thor Olson, did not report any problems with his airplane or make any distress calls before going down. Olson was killed in the crash, which happened during what appeared to be the first nighttime fixed-wing firefighting mission in the state.
The plane’s wreckage “was upright and displayed features of a low-speed, nose-down impact,” according to the brief report.
While the preliminary report provides insufficient details to describe exactly what caused the plane to crash, evidence that the plane rolled inverted before its descent could indicate that the pilot lost control, according to Greg Feith, a Colorado-based former NTSB investigator.
If the wings were rocking after the pilot dropped the retardant, on the pull out, it could suggest that the plane stalled as the pilot was trying to fly away, Feith said.
“If you get the airplane too slow, you have insufficient airflow over the wing to create sufficient lift to support the weight of the airplane and the airplane will go into what’s called an aerodynamic stall,” Feith said.
The plane’s low-speed, nose-down crash is also characteristic of an aerodynamic stall, he said.
The fact that Olson may not have made a distress call to those on ground could mean a sudden crash.
“It probably happened very quickly. He was trying to fly the airplane, he had no time to think about anything else than fly or control the plane,” Feith said.
Flying at low altitudes at night is especially challenging due to reduced visibility, he said. Unlike during the day, when pilots have about 180-degree visibility, night-vision goggles used by firefighting pilots at night reduce visibility to about 40 to 50 degrees of forward visibility.
Gusty winds in the mountains can make flying in the dark more difficult.
“Because of limitations of the night-vision goggles, he may have mistakenly thought that he was further than he actually was to the terrain,” Feith said. “All of these combinations of factors caught up to him as he was trying to maneuver out of the area where he was dropping the retardant.”
The fire’s glow and lights can also blind the pilot while using the goggles.
Olson was an experienced pilot with more than 8,000 hours of flying experience, including more than 1,000 hours of flying with night-vision goggles. Moments before the crash, he reported that conditions were turbulent and that he planned to return to an airport in Loveland, according to the Larimer County Sheriff’s Office.
Olson was flying a single-engine Air Tractor AT-802A, which is similar to a crop dusting airplane. He worked for CO Fire Aviation, which is based in Fort Morgan. The company has been trying to spread the use of nighttime aerial firefighting missions by pilots wearing night-vision goggles.
Though night-time aerial firefighting missions are rare in Colorado, the Larimer County Sheriff’s Office asked CO Fire Aviation for support in the hopes of getting ahead of the Kruger Rock fire, officials said last month.
The National Transportation Safety Board will continue to investigate the crash. It can take more than a year for investigators to release a final report on what caused the aircraft to go down.