Helicopter Crash During External Load Operation at Chimney Site

Casualties unknown • Pautzfeld, DE

A pilot was killed when an Eurocopter AS 355 F2 struck a chimney structure while attempting to lift a heavy component during an external load operation.

What happened

On December 20, 1999, an Eurocopter AS 355 F2 was engaged in an external load operation at a 130-meter-high chimney in Pautzfeld. The mission involved moving a condenser separator (TWA) from a working platform to the ground. After successfully delivering a preliminary load, the pilot attempted a second approach to lift the TWA.

During the lifting process, the helicopter drifted from its position over the load and lost altitude. As the aircraft moved toward the western side of the platform, the main and tail rotors made contact with the chimney's superstructure. The helicopter fell vertically, striking the concrete ground at the base of the chimney. During the descent, the aircraft also struck a factory hall, which caused the tail boom to break away.

The investigation

The BFU investigation examined the wreckage and interviewed witnesses, including technicians on the working platform. Physical evidence showed that the tail rotor blades were severely damaged and one blade had broken at the root. The investigation also reconstructed the configuration of the lifting gear, finding that the lifting chains had become tangled and unevenly tensioned due to the geometry of the TWA and the chimney structures.

Investigators also reviewed the flight company's operational procedures. It was noted that the pilot, who was also the flight operations manager, had decided to forgo an onboard observer to save weight, based on a calculated load of 800 kg. The ground-based signalman was unable to monitor the critical phase of the load attachment from 130 meters below.

Findings

  • The pilot underestimated the complexity of the operation and the spatial constraints between the chimney structures.
  • The absence of an onboard observer meant the pilot lacked essential visual references to monitor the precise position of the load and the aircraft relative to the chimney.
  • An unexpected tensioning of the lifting gear occurred because one of the three lifting chains had shortened by 3 meters, causing the load to pull the helicopter out of position earlier than anticipated.
  • The pilot failed to decide to jettison the load in a timely manner once the instability began.

Probable cause

The accident was caused by the pilot's failure to promptly release the external load after the helicopter was pulled out of position by an unexpectedly tensioned lifting chain, a situation exacerbated by the lack of an onboard observer to monitor the load's position.

Frequently asked questions

What happened in the 1999-12-20 EUROCOPTER AS 355 F2 accident near Pautzfeld, DE?

A pilot was killed when an Eurocopter AS 355 F2 struck a chimney structure while attempting to lift a heavy component during an external load operation.

What aircraft was involved and where did it happen?

The accident on 1999-12-20 involved a EUROCOPTER AS 355 F2, at Pautzfeld, DE.

What was the probable cause of the accident?

The accident was caused by the pilot's failure to promptly release the external load after the helicopter was pulled out of position by an unexpectedly tensioned lifting chain, a situation exacerbated by the lack of an onboard observer to monitor the load's position.

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