What happened
On May 27, 2018, at 16:40 LMT, a crew was preparing for a medical mission to Stęszew from EPPO Poznań. As the pilot began the engine start sequence, a paramedic boarded the cabin to prepare the medical equipment. While accessing the medical cabinet, the paramedic observed sparking near the structural frame where the cabinet is mounted. The sparks were observed falling onto the medical oxygen valves. The paramedic immediately alerted the pilot and signaled to abort the start procedure. The engine start was subsequently halted.
The investigation
An investigation conducted by the operator's technical team revealed that the sparking was caused by a chafed power supply cable for the medical drawer, which resulted in an electrical short circuit. Following the incident, the operator consulted with the Technical Coordination Center and decided to remove the helicopter from service. To ensure continued airworthiness, the operator's management ordered a temporary grounding of the entire fleet to inspect the power wiring for the medical cabinets.
Following consultation with the medical cabin manufacturer, the damaged drawer was sent to the manufacturer for analysis. On June 5, 2018, the manufacturer issued Service Bulletin ASB-18-007, which mandated the deactivation of the medical cabinet in the event of wiring damage. After inspections were completed across the EC 135P2+ fleet, the aircraft were returned to service.
Findings
- The direct cause of the incident was the chafing of the insulation on the power supply cable for the medical drawer, which led to a short circuit.
- The sparks posed a significant risk due to their proximity to medical oxygen valves.