The pilot of the experimental, amateur-built biplane reported that, following a normal initial climb from the runway at the airport in Bowling Green, Kentucky, about 100′ above the ground, the Curtiss JN4D started an uncommanded left turn, followed by a descent.
He added that it became apparent that the flightpath was into the tree line, and he “attempted to climb to possibly maintain at least an altitude to clear the trees, but to no avail, nearly stalling.”
The biplane hit the trees, sustaining substantial damage to the wings and fuselage.
The pilot noted that the biplane is “not very stable once in a flying configuration, any air mass (gusts) change can disturb the balance and result in self-induced turns, climbs and descents. These movements have to be countered immediately because of the relative size (small) of control surfaces (rudder, ailerons). And corrections are slow, possibly resulting in loss of altitude. Pilots expect these upsets and become alert for them.”
The automated weather observation system on the airport reported, about the time of the accident, the wind was from 360° at 5 knots. The pilot was departing from runway 03. The calculated density altitude was 1,897′.
Probable cause: The pilot’s exceedance of the biplane’s critical angle of attack during initial climb, which resulted in an aerodynamic stall and collision with trees.
NTSB Identification: GAA17CA488
This August 2017 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.