On September 05, 2017, about 1430 Pacific daylight time, an experimental Cobalt Co50 Valkyrie airplane, N523CA, landed hard at the Castle Airport, Atwater, California. The airline transport pilot was not injured; the airplane sustained substantial damage. The airplane was registered to and operated by Cobalt Aircraft Industries, Inc. as a Title 14 Code of Federal Regulations Part 91 test flight. Visual meteorological conditions prevailed and no flight plan was filed for the local area flight which originated from Atwater about 1405.

The airplane, serial number PX-04, was manufactured in October 2016 and registered under an Experimental Research and Development airworthiness certificate. The airplane had undergone four previous flights and the accident flight was the pilot's first flight in a Cobalt aircraft. The purpose of the flight was for the pilot to perform an evaluation of handling qualities at various configurations specified in the test card.

The pilot stated that he started the flight by making two test runs down the runway. During both test runs he briefly lifted the airplane off the surface in an effort to check the rotation performance. On both attempts, he had full aft back pressure on the control stick and the airplane would not rotate off the runway. The pilot determined that the center-of-gravity (CG) was too far aft and the ground team added 2o to the adjustable ground trim, equating to a total of 10o. The pilot configured the airplane for a departure from runway 31, planning for a rotation speed of 75 kts.

The pilot further stated that after rotation, with the airplane about 50 ft above ground level (agl), he experienced extreme difficulty controlling the airplane. As the airspeed increased, he began to attain some controllability and climbed to about 1,400 ft agl. He determined that the ailerons were ineffective but was able to use the rudder for directional control. The pitch stability was sporadic with him experiencing intermittent pitch up and down movements. After about 20 minutes of manipulating the flight controls and practicing climbing and descending using the trim, he managed to stabilize the airplane around 90 kts. He reasoned that he would be able to land the airplane while configured at an increased airspeed using steady thrust control and the rudder for directional control. During landing, with the airplane about 10 ft above the runway surface, the airplane experienced a loss of lift and landed hard. The impact resulted in the right landing-gear leg separating and the airplane subsequently made a 180o turn; the right-wing spar sustained damage.

A representative from Colbalt stated the company reviewed the video recordings and onboard recorders. The recordings disclosed that after a faster-than-expected rotation speed between 80-85 kts, the airplane had no roll control. For the test flight they had an increased weight and had changed the winglet position which contributed to a loss of aileron effectiveness.