What happened
On August 23, 2007, an EUROCOPTER EC135 P2+ was preparing for a primary emergency mission at Mannheim-City airfield. The aircraft was positioned on a mobile transport platform and connected to an external power supply. Following standard procedures for the previous aircraft type used at the station, the physician disconnected the power cable and placed the plug on the ground in front of the platform.
As the pilot transitioned the helicopter into a hover and began to accelerate forward, the aircraft suddenly entered a steep nose-down attitude, reaching an angle of approximately 80 degrees. The rotor blade tips passed within one meter of the ground. During this maneuver, the aircraft became tethered to the transport platform, dragging the 1,940 kg platform approximately 10 meters along the ground. The aircraft then rolled around its longitudinal axis and underwent a 180-degree yaw. The tension eventually caused the cable to detach from the skid, allowing the pilot to regain control and perform a controlled landing. There were no injuries and no damage to the aircraft.
The investigation
The BFU examined the sequence of events, the configuration of the transport platform, and the transition in aircraft types at the medical center. The investigation focused on why the power cable became entangled and why the pilot was unable to detect the hazard during the initial takeoff phase. The investigation also reviewed the station's operating procedures, which had been established based on the requirements of a different helicopter model.
Findings
The formation of a cable loop around the right skid was the primary cause of the incident. The physician inadvertently created a loop of the black power cable around the tip of the right skid while placing the plug on the ground. Because the cable and the skid were both black, the lack of visual contrast made the loop difficult to detect.
Several contributing factors were identified:
- Change in aircraft type: The station had recently transitioned from using the BK117 to the EC1135 P2+. Unlike the previous model, the external power socket on the EC135 is located at the rear right of the fuselage. This required the cable to be routed around the aircraft, passing over the right skid.
- Time pressure: The requirement to launch an emergency mission within 120 seconds created tension and urgency during the startup sequence.
- Inadequate platform configuration: The transport platform was configured for the older aircraft type, placing the voltage converter in a position that necessitated routing the cable over the landing gear.
Safety action
The operator has since modified the transport platform by relocating the voltage converter and routing the cable along the edge of the platform to prevent snagging. Additionally, the operator has updated training protocols and implemented color-coded markings for external power cables.