What happened
On May 3, 2014, a Bell 206L-3 helicopter, registration PT-HTQ, was conducting a scenic flight near Aquiraz, Ceará, carrying a pilot and five passengers. Approximately 20 minutes into the flight, the pilot heard a loud, abnormal noise originating from the aircraft's transmission system. Immediately following this noise, the pilot experienced a significant loss of lateral control (roll) via the cyclic command. When attempting to increase power using the collective, the aircraft tended to tilt to the left.
In response to the mechanical failure, the pilot executed a forced landing in the sea, approximately 200 meters from the shore. The aircraft struck the water with its tail rotor making initial contact due to a nose-high attitude, causing the helicopter to capsize and sink to a depth of approximately 9 meters. The occupants successfully evacuated the aircraft through the main doors and were assisted to the beach by nearby swimmers. All 6 occupants (the pilot and five passengers) were unharmed, though the aircraft sustained substantial damage to the engine, transmission, main and tail rotors, cockpit, and rear fuselage.
The investigation
The CENIPA investigation focused on the mechanical failure of the transmission components. After the wreckage was recovered by the Fire Department 48 hours later, investigators examined the debris and found a fracture in the right front Link Assembly, a component that connects the airframe to the main rotor transmission.
Laboratory analysis conducted by the Department of Aerospace Science and Technology (DCTA) revealed that the fracture was caused by fatigue. Scanning Electron Microscopy (SEM) and stereoscopic analysis identified impact marks, deformations, and evidence of material fatigue. Furthermore, investigators discovered that the elastomeric components within the Link Assembly and Arm Assembly were covered in a layer of sealant. This sealant was not authorized by the manufacturer's maintenance manual and had effectively hidden the degradation of the polymer material.
Findings
- The primary cause of the failure was the fracture of the right front Link Assembly due to fatigue.
- The application of sealant over the elastomeric components prevented the inspection of the material's condition, masking the degradation of the polymer.
- The degradation of the elastomeric material led to excessive play (looseness) in the metallic components, inducing vibrations and unforeseen stresses that accelerated the fatigue process.
- Evidence of manual sanding/abrading was found at the fatigue initiation site.
- Maintenance supervision was inadequate, as the unauthorized use of sealant was not identified during routine inspections.
Safety action
CENIPA issued the following recommendations to the National Civil Aviation Agency (ANAC):
- Ensure that maintenance procedures performed by the maintenance facility (TC Oficina de Manutenção de Helicópteros Ltda.) on Bell 206L-3 models strictly adhere to the manufacturer's manual.
- Improve the mechanisms for the supervision of maintenance services performed by the aforementioned facility.