Mk11 Stores Ref: 6D/2248247 | Drawing No: MX2468-738C
The Mk11 PEC was only used in the RAF for Vulcan B2 and Victor K2 rear crew.
A "Swivel Seat Type" PEC for low altitude, it provided connections for: breathing oxygen, bail-out oxygen cylinder, and communications.
Modification MX98 introduced a new coupling to the aircraft hose, making this the MK11, and replacing the Mk7 PEC, as explained in the quote below.
Note: This PEC is commonly know as an "SSC", or Swivel Seat Conenctor, but this term is absent from documentation I've found so far.
Quote:
The oxygen mask hose assembly Mk 11 is a low altitude assembly used by rear crew members of Vulcan and Victor aircraft. It is designed to replace the oxygen mask hose assembly Mk 7 by the embodiment of Modification MX98 which introduced the personal hose assembly coupling Mk 2 in lieu of the quick release ocygen connector. The assembly permits high altitude bail-out without loss of the pressure breathing facility from the emergency oxygen system.
This image shows a Mk11 PEC, and clearly depicts the personal hose assembly coupling Mk2 at the bottom.
Unfortunately the way this image has been taken, the personal hose assembly coupling Mk2 is obscured slightly and appears at first glance like the quick release connector of the Mk7 PEC, but is not.