Beartrap (hauldown device)

A helicopter hauldown and rapid securing device (HHRSD) or beartrap enables helicopters to land on and depart from smaller ships in a wide range of weather conditions.
In the mid-1950s, the navies of the world were faced with the challenge of how to land a large helicopter on a rolling, pitching flight deck of a smaller ship. The problem was solved in the early 1960s when the Royal Canadian Navy's Experimental Squadron 10 (VX 10), based at Shearwater, in collaboration with Dartmouth's Fairey Aviation, developed the world's first HHRSD. The CH-124 Sea King was the first Royal Canadian Navy helicopter to be equipped with this system.
To use the beartrap, a helicopter hovers over the landing pad on the deck and lowers a line with an attached probe on the end. This probe is attached by the deck crew to a heavier cable that passes through the centre of the beartrap from a winch below the flight deck. The cable is pulled back up and secured to the helicopter. The pilot then increases power to balance the pull of the winch with the lift of the helicopter. This synchronizes the helicopter with the ship's movements and puts the helicopter in the "high hover" position. As the pilot decreases the power, the helicopter is slowly pulled by the winch to the "low hover" position just above the deck while maintaining sync with the ship. When the landing safety officer (LSO) determines that a relatively quiet moment is approaching, he instructs the pilot to land. The beartrap is then "closed" to capture the helicopter's main probe, securing the aircraft to the flight deck. The tail is secured by a second probe.
Once the helicopter is secured and straightened, the beartrap is used to move the aircraft in and out of the hangar. This allows movement in and out of the hangar in more severe conditions than if aircraft had to be towed in the conventional way.
The HHRSD was subsequently adopted by navies around the world, including the United States, Australia, and Japan. Other navies use different helicopters aboard different escort ships with a broadly similar system of a probe or grappling device lowered on a steel cable into a flight deck grating, before winching itself down while secured to the deck of a pitching vessel in heavy seas.