What happened
On July 4, 2022, an experimental ANSSEC 180, registration PP-XDO, was conducting a private flight from São Sebastião do Passé to Ibotirama, Bahia. The aircraft was carrying a pilot and one passenger. During the cruise phase, approximately 136 nautical miles from the destination, the pilot experienced intense vibrations originating from the powerplant and a noticeable loss of engine thrust. Although engine oil temperature and pressure remained within normal operating ranges, the engine RPM gradually decreased.
The pilot performed an engine shutdown. During the subsequent emergency descent, the crew visually confirmed that the tip of one propeller blade had fractured and was missing. The pilot executed an emergency landing in a field at Fazenda Abençoada, Ruy Barbosa, where the aircraft subsequently struck the ground (pilonagem). Despite the substantial damage to the aircraft, both occupants were uninjured.
The investigation
CENIPA investigators examined the aircraft and the fractured propeller component. The investigation found that the pilot was properly licensed and qualified for the flight, and the aircraft held a valid Airworthiness Certificate (CVA). However, investigators could not access maintenance records or flight hour logs to verify recent maintenance history.
A failure analysis conducted by the Materials Division of the Institute of Aeronautics and Space (IAE) focused on the fractured propeller blade. Metallographic analysis revealed that the fracture surface exhibited "beach marks," which are characteristic of material fatigue. The examination identified corrosion pits on the upper surface of the blade. These pits originated from coarse sanding marks left from a previous maintenance procedure. These surface irregularities acted as stress concentrators, leading to intergranular corrosion and the eventual initiation of a fatigue crack.
Findings
- The propeller blade failure was caused by material fatigue.
- The fatigue crack initiated at a corrosion pit on the blade's upper surface.
- The corrosion pits were triggered by improper sanding marks (coarse sanding) during a previous maintenance or repair procedure.
- Inadequate aircraft maintenance contributed to the occurrence.