Abstract: The invention provides a release device for a secondary parachute canopy intended to operate when during a descent after a main parachute canopy should have been opened by normal operation, the rate of descent exceeds a chosen value indicating some form of failure of the main canopy, comprising a negative rate diaphragm arranged to experience atmospheric pressure on a first side and a reference pressure on the opposite side, an operating member which is movable between a canopy retaining position and a canopy releasing position by movement of the diaphragm, a valve arranged to selectively open the chamber to atmospheric pressure to inhibit operation of the diaphragm, an air bleed arranged to allow air to enter the chamber during a descent to balance the atmospheric pressure on the diaphragm, and a float valve sensitive to rate of descent arranged to close the bleed when a chosen rate of descent is exceeded, thus to trap the reference pressure in the chamber and to apply operating differential pressure to the