What happened
While cruising at approximately 1,500 feet AGL, a Piper Apache experienced a catastrophic structural failure. An eyewitness observed the vertical stabilizer begin to oscillate before it completely separated from the aircraft. Following this separation, the airplane descended and struck a multiple family dwelling.
The investigation
Examination of the wreckage determined that the outboard wing panels had also separated from the aircraft in flight. This secondary failure was caused by downward bending forces that were induced after the initial in-flight separation of the horizontal stabilizer.
The horizontal stabilizer was recovered near the vertical stabilizer, separate from the main fuselage and wing wreckage. The investigation found that the horizontal stabilizer had separated during flight via a horizontal twisting motion that pushed the left tip of the component rearward. Investigators noted an impact mark on the left outboard leading edge of the horizontal stabilizer that was consistent with a soft bodied impact occurring prior to ground impact. While a witness reported seeing birds in the vicinity, no evidence of blood, feathers, or bird remains was found on the stabilizer, elevator, or at the accident site. Additionally, while aluminum and fiberglass components were mounted forward of the empennage, there was no residue indicating they had been struck.
Structural analysis focused on the attachment points where the vertical stabilizer assembly connects to the fuselage. The damage indicated that these four attach points failed toward the left. Although two of the forward attach points were torn out of the horizontal stabilizer during the separation, three of the four bolts attaching the horizontal stabilizer to the fuselage were recovered. Compression damage to the lower skin near the aft, left attach point indicated it was securely attached at the time of failure. There was no evidence to suggest that any attach points were unsecured prior to the accident.