What happened
On September 5, 2017, at approximately 19:00 UTC, a Neiva EMB-712, registration PT-NVH, was conducting a private flight from Belo Horizonte to Biritiba-Mirim. The aircraft was carrying a pilot and one passenger. While cruising at 6,500 feet, a portion of one of the propeller blades fractured.
Following the structural failure, the crew executed engine shutdown procedures and transitioned into a glide. The pilot successfully performed an emergency landing in an uninhabited area near Pedralva, Minas Gerais. The aircraft sustained light damage, and both occupants were reported uninjured.
The investigation
CENIPA investigators examined the aircraft's maintenance records and conducted laboratory analysis on the fractured propeller blade at the Institute of Aeronautics (IAE). The investigation found that while the pilot held valid medical and flight certifications, and the aircraft possessed a valid airworthiness certificate, the maintenance logs for the airframe, engine, and propeller were not up to date. Furthermore, there were no records of compliance with three specific Airworthiness Directives (ADs) related to the propeller model.
Laboratory testing of the fractured blade revealed that the failure was caused by fatigue. Microstructural analysis showed grain growth and a reduction in mechanical hardness in the fractured region compared to the intact blade. This degradation was attributed to heat exposure that reached temperatures high enough to cause recrystallization.
Findings
- The propeller blade fracture was caused by material fatigue resulting from improper heat treatment.
- The propeller had likely been subjected to unauthorized heating, possibly in an attempt to repair a previous deformation, which violated the manufacturer's repair manual and FAA Advisory Circular 20-37.
- Maintenance records for the airframe, engine, and propeller were not properly updated.
- There was no documented evidence of compliance with three relevant Airworthiness Directives (AD 69-09-03 R3, 2003-13-17, and 2005-14-11) during the propeller's last overhaul.