ERA25FA185 · MX Aircraft Tech PTY Ltd MXS

The pilot of the aerobatic airplane was on approach to a runway at the destination airport at the conclusion of a cross-country flight. According to a witness, and electronic data recovered from avionics onboard the airplane, the airplane leveled off about 50 ft above the runway and flew straight down the runway for several hundred feet. The airplane then pitched up and then down before it pitched up to a nose high pitch attitude and climbed several hundred feet. The airplane then rolled 90° to the left, pulled over the top of a loop, and descended before impacting the ground.

Postaccident examination of the airplane at the accident site revealed that that a counterweight plug that normally would have been installed in the left elevator was not present and was found on the ground about 10 ft behind the wreckage. The counterweight plug for the right elevator was found installed and tight. The left elevator counterweight plug threads were intact, about half of the circumference of the counterweight plug displayed gouging, and an area showed evidence of paint transfer. The horizontal stabilizer structure adjacent to the left elevator position where the counterweight plug would have been installed displayed dents and paint scrapes consistent with contact with the counterweight plug. A washer beneath a screw secured to the horizonal stabilizer structure (near where the paint scrapes were observed) was also dented. Metallurgical examination revealed that both the washer and screw had thickness profiles that matched the marks in the outer diameter edge on the counterweight plug and that the marks were consistent with the washer having made repeated contact with plug.

The elevator counterweight plugs were part of a custom feature that the pilot requested the airframe manufacturer incorporate into the elevator during its construction. The airframe manufacturer described the plugs as a short-term solution and they did not provide any instructions for continuing airworthiness, to include torque values to be used when installing the plugs. The manufacturer also stated the plug design incorporated an o-ring that would serve as a secondary locking mechanism. No o-ring was found on the recovered plug at the accident site, nor was one found on the still-installed right elevator’s counterweight plug. Additionally, the plugs found installed on the accident airplane differed dimensionally from those specified in a design document provided by the airframe manufacturer.

Based on the available information, it is likely that the left elevator counterweight plug loosened during the flight until it made contact with the washer and screw in the horizontal stabilizer, sufficient to jam the elevator. This ultimately resulted in the pilot being unable control the airplane during the landing, and the subsequent impact with terrain.

Verbatim NTSB analysis and probable cause from the NTSB dataset