What happened
On January 13, 2009, a HB 350B helicopter, registration PT-HML, operated by the Santa Catarina Military Police Aviation Battalion, was conducting operational training at the Hercílio Luz Aerodrome in Florianópolis. The flight crew was performing a simulated rappelling descent over a grassy area near runway 21.
During the descent procedure of the crew member positioned on the right side of the aircraft, the locking sleeve of the carabiner failed. This failure caused the carabiner to unintentionally open, disconnecting it from the descender (figure-eight). Consequently, the rappeller lost connection to the safety line and fell uncontrollably to the ground, resulting in serious injuries.
The investigation
CENIPA investigators examined the equipment and the sequence of events leading to the detachment. The investigation found that during the preparation for the descent, the descent cable was positioned on the opposite side of what was intended. When the crew member attempted to correct the cable position without disconnecting the hardware, the carabiner and descender became misaligned.
Because the cable was slack, the components were not properly aligned, causing uneven tension during the start of the descent. This stress caused the protective sleeve of the aluminum carabiner to rupture against the eye of the descender. Furthermore, the investigation noted that the carabiner was only partially threaded (not fully locked), which facilitated the failure. The investigation also identified that the crew member's leather gloves were inadequate, as the lack of protection on the index and thumb fingers led to friction burns, which further contributed to the crew member losing their grip on the cable before impact.
Findings
- Improper hardware alignment: The crew member repositioned the descent cable while the carabiner was still attached to the descender, causing the pieces to be misaligned and subject to uneven tension.
- Incomplete locking: The carabiner was only partially threaded, meaning the locking mechanism was not fully engaged.
- Inadequate equipment: The aluminum carabiner used was susceptible to mechanical wear; investigators noted that steel carabiners would have been more suitable for such high-stress rescue missions. Additionally, the crew member's gloves lacked sufficient finger protection.
- Training and supervision deficiencies: There was a lack of continuous oversight for operational training, and the frequency of rappelling maintenance training (only once per year) was insufficient to maintain proficiency. The training phraseology used was also found to be inadequate for ensuring all connections had been verified.