Nowadays the greatest part of the transports is done using this equipment. At the beginning instead this technique was used when large quantities of material had to be transported. In these cases usually two wood platforms were erected one parallel to the other. Then the helicopter landed on them and the cargo was set in position and fixed to the barycentric hook.
The picture n° 1 taken in Ambrì in February 1955 during the "St. Gotthard action", shows the Bell 47G HB-XAE piloted by Leo Kunz while landing on the special platform. On the terrain it is visible an oil drum ready to be transported on the massif of the St. Gotthard where a group of workers is repairing an electric power line damaged by an avalanche. The helicopter is equipped with a "Siren" cargo sling kit fitted to the helicopter center frame, near the centre of gravity. This installation featured a manual release. The man near the platform help the pilot with hand signs to land correctly. In the early years of activity the pilots were not in radio contact with the ground crew. The first "Walkie-Talkie" were too much expansive, heavy and had a limited range. Moreover the radio equipment was often taken down to lighten the helicopter.
In 1955 Heliswiss built a new equipment using light aluminium tubes which was fixed to the undercarriage. This equipment prevented the horizontal rotation of the cargo suspended on the cargo sling during the flight.
On the picture n° 2 taken in Summer 1955 this equipment is visible on the Bell 47G HB-XAK while it transports some wood panels used for the costruction of a hut in the Linthtal/GL. This equipment was however soon abandoned.
Much later to observe the hook and unhook manoeuvres the pilots asked their mechanics to install a rear view mirror in front of the cabin.

HAB 12/2009