Accident Sequence
A Piper Apache was cruising at approximately 1,500 feet above ground level when a witness observed the vertical stabilizer begin to oscillate. The stabilizer then separated from the aircraft. Following this event, the airplane descended and struck a multiple family dwelling.
Wreckage Examination
Post-accident examination of the wreckage revealed that the outboard wing panels had separated from the airplane during flight. This separation was attributed to downward bending forces that occurred after the horizontal stabilizer had detached in flight. The horizontal stabilizer was found adjacent to the vertical stabilizer, apart from the main fuselage and wing wreckage. It had separated in a horizontal twisting motion, which displaced the left tip of the horizontal stabilizer rearward.
An impact mark was observed on the left outboard leading edge of the horizontal stabilizer, consistent with a soft-bodied impact that happened before ground contact. Although a witness reported seeing several birds flying in the area at the time of the accident, a detailed examination of the left horizontal stabilizer and elevator found no evidence of blood, feathers, or bird remains. A thorough search of the accident site also failed to yield any bird carcass or feathers. Various aircraft components, made of aluminum and fiberglass, were located forward of the empennage, but the impact mark exhibited no residual evidence of having been struck by either material. Consequently, the source of the soft-bodied impact could not be determined.
Structural Analysis
The vertical stabilizer is attached to the horizontal stabilizer, and this assembly is then secured to the fuselage through four attach points. Damage to the vertical stabilizer attach points indicated that they failed toward the left (as viewed from the rear looking forward) and were still firmly attached to the horizontal stabilizer at the time of failure. Three of the four bolts that secure the horizontal stabilizer to the fuselage were recovered. The forward two attach points were torn out of the horizontal stabilizer during the in-flight separation. Compression damage to the lower skin immediately forward of the aft left attach point suggested that it was securely attached. No evidence was found to indicate that any of the attach points were unsecured prior to the accident.