What happened
On May 19, 2005, a Schweizer 269 C, registration PT-YZS, was conducting a local flight instruction mission at Jacarepaguá Aerodrome (SBJR) in Rio de Janeiro. The flight involved an instructor and a student pilot. During the third landing attempt on runway 02, the student pilot touched the ground and began reducing the collective pitch.
As the aircraft made contact, one skid was positioned on the white runway marking while the other was on the asphalt, creating different surface textures under the skids. Immediately upon touchdown, the helicopter entered a state of severe vibration throughout the entire structure. Although the instructor attempted to intervene and pull the aircraft back into the air to avoid the impact, the vibration could not be arrested, leading to heavy damage to the airframe. Both occupants escaped the incident without injury.
The investigation
CENIPA investigators examined the aircraft's maintenance history and the physical evidence at the scene. Analysis of the dampers showed they had been displaced due to the impact forces, which prevented comparative testing. However, vibration records from a previous maintenance check indicated the main rotor was within manufacturer limits.
Investigators also noted an excess of grease on the upper main rotor area near the dampers. While the maintenance manual specifies that this area should be clean and lubricated without excess, investigators determined the grease was likely not the primary cause of the loss of control due to the short duration of exposure. The investigation also highlighted that the lack of a suitable grass training area at the aerodrome forced maneuvers to be performed on paved surfaces, increasing the risk of ground resonance.
Findings
- Ground resonance triggered by the interaction of different surface textures (asphalt and runway marking) during touchdown.
- Inadequate training infrastructure, as the lack of a grass area necessitated maneuvers on pavement that are prone to causing structural damage.
- Potential improper application of flight controls by the student pilot during the landing phase.
- Possible lack of effective cockpit coordination and delayed intervention by the instructor.
- Maintenance oversight regarding the accumulation of excess grease near the dampers.