Accident Overview
On May 9, 2020, at approximately 0645 central daylight time, an experimental Titan Tornado S airplane, registration N318WH, was substantially damaged in an accident about 3 miles north of Haskell Airport (2K9), Haskell, Oklahoma. The pilot sustained serious injuries. The flight was conducted as a Title 14 Code of Federal Regulations Part 91 test flight.
Pilot's Account
The student pilot reported that the airplane had experienced uncommanded yaw on previous flights. After researching and consulting with the airplane kit manufacturer, he installed vortex generators, which did not eliminate the yaw. He then attached makeshift winglets made from ½-inch plywood and aircraft speed tape to the stabilator. He did not consult the manufacturer about this modification. The uncommanded yaw ceased during a test flight with the makeshift winglets. Subsequently, he fabricated new winglets from composite material and attached them with glue and rivets. He completed three to four test flights in the traffic pattern without logging the modification in the maintenance logbooks, as he was still testing.
On the accident flight, the pilot intended to test the winglets away from the airport at a higher altitude. He departed 2K9 and climbed at about 600 feet per minute to 2,000 ft. The airplane flew normally until he decreased the pitch attitude. Suddenly, the airplane vibrated aggressively, and the pilot described a sensation that "the tail was thumping." He reduced engine power and descended, but the vibration continued. He pitched down for an off-field emergency landing, but the airplane rolled inverted and descended into trees.
Postaccident Examination
A Federal Aviation Administration (FAA) inspector found the airplane in a densely wooded area with the right wing separated and significant impact damage. The stabilator control horn was fractured and disconnected from the push-pull tube. Examination of the control horn revealed that it fractured due to overstress from gross mechanical deformation, with impact damage indicating the stabilator had been actuated from stop to stop during the flight.
Manufacturer's Perspective
An engineer from the airplane kit manufacturer stated that adding winglets to the stabilator changes the control surface's balance and can cause flutter. The stabilator is equipped with a counterweight calibrated for the stock configuration. The engineer had not previously encountered stabilator winglets and stated he would advise a builder against adding them, as they alter the balance.