What happened
On May 8, 2022, a Bell 206B helicopter, registration PT-HQB, was performing a passenger transport flight from Aldeia Terra Nova to Cruzeiro do Sul, Acre. The aircraft was carrying one pilot and six passengers, including two infants. While cruising approximately 20 NM from its destination, the aircraft suffered a sudden loss of engine power. The pilot was forced to execute an emergency landing in a dense, swampy jungle area.
The impact caused substantial damage to the aircraft, including a broken skid assembly and damage to the main rotor blades, main rotor shaft, and the tail rotor. While the pilot and five passengers sustained minor injuries, one passenger suffered serious injuries.
The investigation
CENIPA investigators examined the Allison 250-C20B engine, which was removed and subjected to disassembly and technical analysis. The investigation included microscopic examinations (SEM and EDS) to identify the failure mechanism.
Technical analysis revealed that a Stage 2 compressor blade had detached due to fatigue initiated by corrosion. The presence of high levels of oxygen and chlorine in the crack region confirmed that corrosion-fatable processes were at work. The detachment of this blade triggered a chain reaction, causing the release of additional blades in Stages 2 and 3, which subsequently perforated the compressor housing and caused secondary impact damage to other internal components. Investigators also noted evidence of excessive vibration within the assembly.
Findings
- The primary cause of the engine failure was corrosion-fatigue of the Stage 2 compressor blades.
- The engine compressor showed significant degradation, with corrosion sites acting as the origin for fatigue cracks.
- Maintenance records indicated that while scheduled inspections were performed, there was no evidence that specific procedures for daily engine rinsing (as outlined in CSL 1135) were effectively executed to mitigate corrosive environments.
- There was a possible shortcoming in the execution or supervision of maintenance procedures regarding compressor cleaning and preservation.
- The aircraft was within weight and balance limits, and the pilot was fully qualified and held a valid medical certificate.