Federal Aviation Administration / Flight Standards District Office; Helena, Montana
Aviation Accident Final Report - National Transportation Safety Board:https://app.ntsb.gov/pdf
Investigation Docket - National Transportation Safety Board: https://dms.ntsb.gov/pubdms
Aviation Accident Data Summary - National Transportation Safety Board: https://app.ntsb.gov/pdf
Aviation Accident Factual Report - National Transportation Safety Board: https://app.ntsb.gov/pdf
Skyline Aviation LLC: http://registry.faa.gov/N9004M
NTSB Identification: GAA17CA225
14 CFR Part 137: Agricultural
Accident occurred Monday, April 10, 2017 in LEWISTOWN, MT
Probable Cause Approval Date: 06/20/2017
Aircraft: WEATHERLY AVIATION CO INC 620B, registration: N9004M
Injuries: 1 Uninjured.
NTSB investigators used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.
The pilot reported that, during a low-altitude, practice agricultural application flight, he lost depth perception between the snow-covered ground and overcast sky. He added that the airplane impacted the ground and came to rest after sliding about 500 ft.
The airplane sustained substantial damage to the right wing and fuselage.
The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.
The Federal Aviation Administration’s pamphlet, “Flying in Flat Light and White Out Conditions,” states the following:
Flat light is an optical illusion, also known as “sector or partial white out.” It is not as severe as “white out” but the condition causes pilots to lose their depth-of-field and contrast in vision. Flat light conditions are usually accompanied by overcast skies inhibiting any good visual clues. Such conditions can occur anywhere in the world, primarily in snow covered areas but can occur in dust, sand, mud flats, or on glassy water. Flat light can completely obscure features of the terrain, creating an inability to distinguish distances and closure rates. As a result of this reflected light, it can give pilots the illusion of ascending or descending when actually flying level. However, with good judgment and proper training and planning, it is possible to safely operate an aircraft in flat light conditions.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
The pilot’s failure to maintain altitude during low-altitude maneuvers in flat light conditions.
The pilot reported that during a low altitude, practice aerial application flight, he lost depth perception between the snow-covered ground and overcast sky. He added that the airplane impacted the ground, and came to rest after sliding about 500 ft.
The airplane sustained substantial damage to the right wing and fuselage.
The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.
Federal Aviation Administration's pamphlet, "Flying in Flat Light and White Out Conditions", which states:
Flat light is an optical illusion, also known as "sector or partial white out." It is not as severe as "white out" but the condition causes pilots to lose their depth-of-field and contrast in vision. Flat light conditions are usually accompanied by overcast skies inhibiting any good visual clues. Such conditions can occur anywhere in the world, primarily in snow covered areas but can occur in dust, sand, mud flats, or on glassy water. Flat light can completely obscure features of the terrain, creating an inability to distinguish distances and closure rates. As a result of this reflected light, it can give pilots the illusion of ascending or descending when actually flying level. However, with good judgment and proper training and planning, it is possible to safely operate an aircraft in flat light conditions.
14 CFR Part 137: Agricultural
Accident occurred Monday, April 10, 2017 in LEWISTOWN, MT
Aircraft: WEATHERLY AVIATION CO INC 620B, registration: N9004M
Injuries: 1 Uninjured.
NTSB investigators used data provided by various entities, including, but not limited to, the Federal Aviation Administration and/or the operator and did not travel in support of this investigation to prepare this aircraft accident report.
The pilot reported that during a low altitude, practice aerial application flight, he lost depth perception between the snow-covered ground and overcast sky. He added that the airplane impacted the ground, and came to rest after sliding about 500 ft.
The airplane sustained substantial damage to the right wing and fuselage.
The pilot reported that there were no preaccident mechanical failures or malfunctions with the airplane that would have precluded normal operation.
Federal Aviation Administration's pamphlet, "Flying in Flat Light and White Out Conditions", which states:
Flat light is an optical illusion, also known as "sector or partial white out." It is not as severe as "white out" but the condition causes pilots to lose their depth-of-field and contrast in vision. Flat light conditions are usually accompanied by overcast skies inhibiting any good visual clues. Such conditions can occur anywhere in the world, primarily in snow covered areas but can occur in dust, sand, mud flats, or on glassy water. Flat light can completely obscure features of the terrain, creating an inability to distinguish distances and closure rates. As a result of this reflected light, it can give pilots the illusion of ascending or descending when actually flying level. However, with good judgment and proper training and planning, it is possible to safely operate an aircraft in flat light conditions.
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