What happened
On June 10, 2015, at approximately 19:15 UTC, a Neiva EMB-712, registration PT-NTH, was conducting a flight instruction mission from São José dos Campos to Guaratinguetá, Brazil. The crew consisted of a flight instructor and a student pilot.
While executing the NDB approach procedure for the orbit at Guaratinguetá Aerodrome (SBGW), the aircraft suddenly experienced loud noises and intense vibrations. The instructor immediately took control of the aircraft, declared an emergency to air traffic control, and shut down the engine. The aircraft subsequently landed on runway 02. Upon inspection on the ground, it was discovered that one of the propeller blades had fractured, and the missing piece of the blade could not be located. The aircraft sustained light damage, and both occupants were uninjured.
The investigation
CENIPA investigators focused their analysis on the propeller's maintenance history and a laboratory examination of the fractured component. The propeller, a Sensenich model, was sent to the laboratory of the Department of Aerospace Science and Technology (DCTA) for stereoscopic failure analysis.
Technical examinations revealed that the propeller blades exhibited multiple impact marks and nicks across their entire surface. The laboratory analysis identified a fracture surface characteristic of material fatigue. The investigation established that a specific nick on one of the blades acted as a stress concentrator, which facilitated the fatigue failure.
Findings
- The propeller blade failure was caused by material fatigue.
- The fatigue process was accelerated by an impact mark that created a point of deformation and concentrated stress within the metal.
- The propeller blades were covered in various impact marks and nicks prior to the flight.
- It is hypothesized that the crew and ground personnel failed to recognize the severity of the existing surface damage during pre-flight inspections.
Safety action
CENIPA issued a recommendation to the National Civil Aviation Agency (ANAC) to work with the São José dos Campos Aero Club to verify the adequacy of their maintenance supervision procedures, specifically regarding propeller inspections.