What happened
On February 22, 2018, an AS350B2 helicopter, registration PT-HYW, was performing a cargo and personnel transport flight from Brasília to Crixás, Goiás. Approximately 30 minutes into the flight, the pilot noticed the hydraulic system emergency light and an accompanying audible alarm. The pilot also noted that the flight controls were becoming increasingly stiff.
In response to the failure, the pilot attempted an emergency landing in a rural area of Santa Rita do Novo Destino. During the final approach, the pilot lost control of the aircraft, causing the main rotor blades to strike the terrain. The helicopter subsequently skidded across the ground, resulting in substantial damage to the airframe, including a fractured tail boom and broken rotor blades. The pilot sustained minor injuries, while the two passengers were uninjured.
The investigation
CENIPA investigators examined the hydraulic system and found evidence of significant wear on the splines of the hydraulic pump shaft. This wear likely interrupted the fluid supply, causing the system pressure to drop below the 30-bar threshold. The investigation also noted that the hydraulic fluid filter-clogging indicator was visible, suggesting fluid contamination.
Regarding the pilot's actions, the investigation found that the pilot utilized the "HYDR TEST" pushbutton on the central console to initiate the hydraulic cut-off, rather than using the designated switch on the collective handle. This specific action caused a high load on the pedals due to the depressurization of the yaw load compensator, which stripped the pilot of pedal control near the ground. Furthermore, investigators noted that while the pilot had completed company-mandated training, previous evaluation sheets had specifically recommended that the procedure for landing with hydraulic cut-off be revisited to achieve ideal proficiency.
Findings
- The hydraulic pump shaft splines were worn, compromising the pump's operation.
- The pilot lost control of the aircraft near the ground due to an improper hydraulic cut-off procedure.
- The use of the "HYDR TEST" button instead of the collective switch led to a loss of pedal control.
- The pilot's decision-making was likely impacted by the stress of the mechanical failure, leading to an attempt at a punctual landing rather than a safer running landing.
- There were indications of potential maintenance discrepancies, including the use of expired grease in the maintenance facility and possible inadequate lubrication of the pump drive splines.