Incident Overview
On 27 May 2018 at 16:40 LMT, the crew of an EC 135P2+ helicopter in Poznań (EPPO) received a medical flight assignment (order no. 199/R9/2018) to respond to an illness in Stęszew. After the pilot occupied the cabin and began the engine start procedure, a paramedic entered and took a seat. While performing pre-flight preparations using the medical cabinet, the paramedic observed sparking near the attachment frame of the cabinet. The sparks fell onto medical oxygen valves. The paramedic immediately notified the pilot, exited the cabin, and signaled for the pilot to abort the engine start. The pilot complied and halted the start sequence.
Technical Findings
Following consultation with the Technical Coordination Center, the helicopter was withdrawn from service. A maintenance mechanic from the Technical Service Station determined that the cause of the sparking was chafing of the insulation on the power cable supplying the medical drawer, which led to a short circuit. The medical cabinet was subsequently deactivated in accordance with MEL procedure 85, section 8.6.2, category C (valid for 10 days).
Fleet-Wide Action
On 28 May 2018, after consulting with the medical cabinet manufacturer, the person responsible for continuing airworthiness management ordered the entire EC 135P2+ fleet to be grounded until inspections of the power harnesses supplying the medical cabinet were completed. On 30 May 2018, the damaged drawer was removed from the cabinet and sent to the manufacturer to establish a procedure for handling such damage. On 5 June 2018, the manufacturer issued Service Bulletin ASB-18-007, mandating deactivation of the medical cabinet in the event of electrical bundle damage. The manufacturer is working on a solution for safe power supply to the medical cabinet. After performing inspections on all EC 135P2+ helicopters, the fleet was returned to service.
Cause
The direct cause of the incident was chafing of the insulation of the power cable supplying the medical drawer, which led to a short circuit.