Background
The accident occurred during a visual approach to an airport situated in a steep mountain valley. The tower controller informed the first officer, who was pilot flying, that a Citation pilot had reported low-level windshear with a 15-knot loss of airspeed on short final about 10 minutes earlier.
Flight and Accident
On the left base leg, the first officer deployed the spoilers. During the final leg, he maneuvered the airplane in an S-turn to correct for a too-steep approach. As the airplane neared touchdown with decreasing airspeed, the captain called for "power" multiple times and then for a "go around." The first officer did not add power for a go-around, and the captain did not take control.
Both pilots reported that, at about 30 feet above ground level (agl), they felt a sensation that the airplane had "stopped flying" with a simultaneous left roll—indicative of an aerodynamic stall—followed by immediate impact with terrain. The airplane struck obstructions, completely separating the right main landing gear and the right flap. It came to rest upright in the dirt alongside the runway, approximately 4,000 feet from the initial impact point.
Damage and Evacuation
The airplane sustained substantial damage to the fuselage and both wings. All eight occupants evacuated through the main cabin door. A substantial fuel spill occurred, but there was no postimpact fire.
Pilot Reports and System Warnings
Both pilots reported no mechanical malfunctions or failures, and neither reported an uncommanded loss of engine power. Data from the enhanced ground proximity warning system indicated seven warning events in the final three minutes. The first warning, for "sink rate," occurred at about 1,317 feet agl during a 3,400-foot-per-minute descent. The last warning, for "bank angle," occurred about 10 seconds before touchdown when the airplane exceeded 42 degrees of bank at about 200 feet agl.
The wind recorded at the airport at the time of the accident would have resulted in a 12-knot variable tailwind with gusts to 18 knots.
Analysis
The evidence shows that the first officer flew a non-stabilized approach with decreasing airspeed during known low-level windshear conditions. He did not properly compensate for those conditions, allowing airspeed to continue decreasing and bank angle to increase until an aerodynamic stall occurred.
Probable Cause
The first officer's failure to maintain adequate airspeed and his exceedance of the airplane's critical angle-of-attack during the final approach in known low-level windshear conditions, which resulted in an aerodynamic stall. Contributing to the accident were the first officer's failure to initiate a go-around when commanded and the captain's lack of remedial action when he recognized that the approach was unstabilized.