British D-Type Partial Pressure Aircrew Flying Helmet
Used for flying at high altitudes in conjunction with a pressure jerkin, in case of a cabin depressurisation. This equipment would allow the aircrew to "get down" safely.
Made by the GQ Parachute company, it is of fabric and rubber construction. It is very similar in appearance to the G-Type partial pressure helmet, but has an aluminium frame around the clear visor.
The purpose of the partial pressure helmet and Jerkin is to attempt to equalise the pressure in the aircrew's lungs with that applied to the outside of the body. This is particualrly important under cabin de-pressurisation at high altitude, where the pressure differential would rapidly increase.
The helmet (much like the pressure jerkin) contains bladders to exert pressure on the head, equal to the oxygen supply pressure at all times.
Images
D-Type partial pressure helmet images kindly supplied by The Science Museum.
