Amateur-built CHALLENGER II SP N65VG accident near Prineville, Oregon

Probable cause

The in-flight failure of the left elevator control torque tube. Contributing to the accident was the improper assembly of the elevator control torque tubes.

NTSB analysis

Witnesses near the accident site reported observing the accident airplane fly near their location at a low altitude. They reported that the airplane oscillated up and down multiple times and that the tail's flight control surfaces appeared to be moving erratically before the airplane descended into terrain.

Postaccident examination of the wreckage revealed that both the left and right elevator control torque tubes were fractured and that the fracture areas were consistent with overload. Also, both the forward and aft set of rivets on the right control tube and the aft rivet on the left control tube that connect the outer sleeve to the smaller portions of the control torque tubes were made of an aluminum alloy material; the manufacturer's assembly instructions require that stainless steel rivets to be installed. Evidence of chafing and impact marks were observed near the separation area of the left control tube, indicating that the torque tube likely separated in flight and restricted the right elevator control movement.

A family member, who had previously flown in the accident airplane with the pilot, reported that the airplane had been experiencing abnormally high vibrations from the tail section during high-speed flight (when approaching about 90 miles per hour [mph]) and that the control stick would slam forward. The mechanic who conducted the airplane's last condition inspection about 3 months before the accident reported that he did not note any abnormal wear on the elevator flight controls. When he flew the airplane after completing the inspection, he noticed a buffet during and after throttling back in descent. The mechanic noted that the pilot had mentioned to him that he had the same problem in addition to the airplane experiencing heavy vibrations and the control stick slamming forward during flight at 90 mph, which is consistent with the family member's statement. The mechanic reported that he and the pilot inserted gap strips between the horizontal stabilizer and elevators. He also stated that the pilot had increased the angle of incidence on the elevators but that he was not sure how or when the pilot performed these adjustments. The airplane maintenance records were not located, and it could not be determined when the torque tube rivets were last installed or when maintenance was last performed on the elevator flight controls.

Text from the NTSB. Open the NTSB docket for WPR13FA400 for the full record.