British Aircrew Mask PEC Combined Oxygen and Mic / Tel
Stores Ref: believed to be 6D/3643 - needs confirming
This special connector was used in the RAF for the Folland Gnat.
A "combined oxygen and mic / tel" connector for low altitude, it provided connections for: breathing oxygen, emergency oxygen, and communications.
A unique design of PEC where the communications contacts are combined within the oxygen connector, making one action to conenct both services, but the loss of intercom was also used as a warning that a lack of oxygen was imminent.
Only used with the P4-Type oxygen mask, which had a special combined oxygen and mic-tel hose and conenctor, which in turn required the G-Type or Mk2A helmet to have a special headset wiring harness installed to usitlise the microphone socket as a headphone socket.
The system was not adopted to other aircraft. This is believed to be mainly because the tiny wires bonded ot the sides of teh oxygen hose of the P4-Type and P4B-Type oxygen masks would break down with use (constant flexing) and the masks hose mic / tel assembly would need replacing. I have witnessed private operators of Gnats bypass this system and use helmets with regular NATO plus for communications by adding a flying lead to the cockpit with NATO socket.
Exhibits
Gnat ejection seat harness
Gnat combined oxygen and mic / tel connector mounted on seat harness. Note the emergency oxygen hose is removed.
It is clearly visible how a similar combined connector is also used to connect the oxygen hose to the aircraft - a Jubilee clip attached to a webbing strap withdraws the connector upon ejection.
Also visible is the short anti-G suit supply hose, but this would normally be fitted to the aluminium clamp on the harness.
This image inside the upper socket shows the electrical contacts for the microphone and telephone elements of the helmet headset, and also illustrates the method of locking the mask hose plug in place using bayonet spigots.
The lower plug (cockpit floor) used a profiled skirt to clip around a sprung ring which would be pulled free on ejection.
RAF Resources
AP1182E, Volume 1, Section 4, Chapter 8, (AL 107, May 1964)
Cross-sectioned drawing showing the Folland Gnat combined oxygen and mic / tel connector.
AP109B-0200-1 (March 1970)
Quote:
Helmet, mask and tube
75. The Integral Protective Helmet, Mk2A flying helmet, a helmet connector and an oxy/mic/tel Type P4 mask is used (fig. 29). The lower plugs of the mask tube and seat hose each incorporate four annular rings to make the mic/tel connections.Mask tube connection to P.E.C.
76. Two external pins are fitted to the mask tube plug and these pins must be inserted fully into the socket slots of the P.E.C. before electrical contact is made with contact blades in the socket.77. The P.E.C socket is provided with a spring-loaded, knurled, outer sleeve and both the socket and sleeve are provided with bayonet slots. The slots in the socket and sleeve coincide only when the sleeve is depressed and this occurs automatically when inserting the mask tube plug, which can be done with one hand, the socket bayonet pins depressing the sleeve. After the plug has been fully inserted, the sleeve returns to its normal position under spring pressure and the plug is locked in the socket. To remove the plug it is necessary to depress the sleeve wit hone hand whilst removing the plug with the other.
78. The plug and socket are so designed that mic-tel communication is broken before oxygen leakage can occur due to partial disconnection; this joint should be checked immediately in the event of communication failure.
AP109B-0200 Fig 27 (March 1970)
This image demonstrates the combined oxygen and mic / tel system as a whole, as used in the Gnat aircraft.
