What happened
On March 17, 2016, an agricultural flight operation was underway near Jaborandi, Bahia, when a Neiva EMB-202, registration PT-UKT, experienced a catastrophic structural failure. The aircraft had departed from Fazenda Santa Maria for a ferry flight to Formosa, Goiás. During the flight, the pilot identified an agricultural landing strip and decided to perform a low pass to assess the surface conditions.
While recovering from the low pass, the left wing of the aircraft separated from the fuselage. Following the loss of the wing, the aircraft entered an uncontrolled descent and struck the ground in a flat, unobstructed area. The impact caused substantial damage to the engine, propeller, fuselage, wings, and cockpit. The pilot sustained serious injuries.
The investigation
CENIPA investigators examined the wreckage, noting that the aircraft components had been moved from the crash site to the operator's farm without authorization, which hindered the initial analysis. Laboratory testing of the wing spar components conducted at the Institute of Aeronautics and Space (IAE) revealed that the failure was caused by a fatigue process.
The investigation found that a crack had initiated at the lower flange of the spar, specifically at the hole of the fifth lower bolt. This fatigue crack propagated through more than 70% of the flange section, significantly reducing its mechanical strength and eventually leading to a final failure due to overload.
Investigators also identified that the installation of the bolt had caused rough threading marks on the surface of the hole, creating stress concentrators. Furthermore, the holes for the five bolts on the left wing semi-spar had been painted, a practice not authorized by the manufacturer. While a recent Airworthiness Directive (AD) had mandated Eddy Current inspections to detect corrosion and cracks, the investigation determined that the cracks were already present and advanced prior to the last scheduled inspection.
Findings
- Fatigue-induced structural failure caused by a crack in the lower flange of the left wing spar.
- Presence of stress concentrators due to improper bolt installation (forced threading).
- Ineffective maintenance oversight, as previous inspections failed to identify the existing cracks.
- Inadequate maintenance supervision and organizational processes regarding the execution of required inspections.