What happened
A Canadian Helicopters Bell 212 helicopter, registration C-GDVG, was performing a sling load operation at Goose Bay, Newfoundland and Labrador, when it experienced a series of mechanical and aerodynamic instabilities. While attempting to lift a military utility trailer using a long-line system, the aircraft was unable to clear the ground cleanly due to excessive weight. As the helicopter transitioned into forward flight, the rear of the trailer struck the tarmac, creating a gouge, and subsequently collided with another sling load on the airfield.
The pilot, flying from the left seat, experienced oscillations known as pylon rock. Believing this instability would subside with increased airspeed, the pilot continued the flight. However, as the aircraft turned back toward the airport, the airspeed decreased, reintroducing the pylon rock and causing the load to strike the ground again. The trailer then entered a stand of trees, creating a sudden deceleration that sent massive rearward forces through the cargo hook. These forces damaged the helicopter's internal control components, specifically jamming the throttle and tail rotor control tubes. The aircraft completed two 360-degree rotations before striking the ground in an upright position. The pilot sustained serious but non life-threatening injuries.
The investigation
The investigation focused on the aircraft's weight, the mechanical failure of the control systems, and the sequence of the load's movement. Investigators examined the helicopter's structural damage, noting that the landing gear cross tubes were driven into the belly and the fuel cell was punctured. The examination of the area beneath the transmission, known as the "Hell Hole," revealed significant damage caused by the cargo hook being pulled backward against the airframe. This damage was linked to the trailer tow bar digging into the ground, which caused the sudden deceleration.
Weight calculations revealed that the helicopter's gross weight was approximately 11,420 pounds, which exceeded the maximum allowable gross weight of 11,200 pounds. Furthermore, the weight exceeded the specific limit for out-of-ground-effect hover, which was 10,900 pounds for the prevailing weather conditions. While the cargo hook featured a load cell, it was determined that the load weight had not been accurately verified during the second pick-up attempt.
Findings
- The helicopter's gross weight exceeded both the maximum allowable gross weight and the maximum allowable limit for out-of-ground-effect hover.
- Due to the excessive weight, the aircraft could not lift the load cleanly, causing the trailer to drag on the tarmac and become unstable.
- The pilot's attempt to release the load occurred too late in the accident sequence.