British Aircrew Underwater Escape / Ejection
The issue of not being able to properly eject under water was realised, and a system for underwater escape was called for.
This article examines the equipment modified for this purpose.
The aircraft which were eqipped with this system were the Buccaneer and Sea Vixen. Other Fleet Air Arm / Royal Navy aircraft of the era (Phantom and Harrier) employed differnt methods. Originally these aircraft has just standard ejection seats designed for land / air use with no way of ejecting under water. This modification gave the existing ejection seats the capability of safely assisting the occupant out of a sinking aircraft.
The extract below from AP4744B-AN describes the system in great detail, so only additional information will be presented here.
Aircrew Equipment Assembly (AEA)
Certain items of the AEA had specila features to facilitate underwater escape.
Personal Equipment Connector (PEC)
Originally the Buccaneer and Sea Vixen both used the Mk4 PEC. The underwater ejection modification entailed adding a small bore hose to the PEC to trigger the life jacket's inflation head, so the modified PEC became the Mk8.
Life Jacket
As it is typical to see PEC's left permanently clipped to life jackets when not in use, having the small bore hose reaching over to the left hand side to reach the bottle, while it is clipped to the D-Ring on the right hand side would hinder donnong / doffing the life jacket; this would require disconnectig the hose every time the aircrew dressed / undressed. This issue, I believe probably led to the bottle being moved ot the right hand side, the same side as the D-Ring the PEC is clipped to. The right hand side is also the side that the PEC is on for the Buccaneer and Sea Vixen. The CO2 bottle capacity was also increased for underwater escape to be able to fully inflate the stole under the pressure of the water.
The RAF / RN AP information I have refers to a "modified LSW" to denote the CO2 bottle being moved to the right hand side. However, I have found a brochure by Beaufort, which mentions the Mk8 and Mk8A being the designations of these life preservers.
Manufacturers Resources
Braufort Life Preserver brochure, date unknown
Quote:
The Mk. 8 and Mk. 8A lifejackets are fitted with an 86 grammme CO2 cylinder and relief valve to permit underwater escape from aircraft.
Service Images
Fleet Air Arm / Royal Navy 809 Squadron Buccaneer Aircrew
This image clearly shows the Mk8 life jacket, having the CO2 bottle moved to the right hand side, special bottle release head with side hose connector. The special release head is connected to the small bore hose of the Mk8 PEC. Also shown is a Mk2A helmet.
RAF / RN AP Resources
AP4744B-AN, Part 1, Capter 13, Paragraphs 14 and 15, AL6, 1969
This extract from the Buccaneer S Mk.2 Aircrew Notes does a fantastic job of describing the system. It is assumed that the Sea Vixen may have used a very similar (if not the same) system for underwater ejection. This AP uses the term LSW (Life Saving Waistcoat), later AP's use the term LSJ (Life Saving Jacket).
Quote:
14 Underwater escape system, general description
(a) Provision is maded for a fully automatic underwater escape system. This is capable of ejecting an unconscious occupant from the aircraft, separating him from his seat and supporting him on the surface by his fully inflated LSW, without any action being necessary on his part. The main components and their function are shown in the following sub-paras.
(b) Water pressure sensing unit
Stainless steel pipes lead from a static pressure hole, in the port cockpit skin, to the pressure sensing diaphragm assembly of a compressed air bottle firing unit at the base of each ejection gun. When the sinkig aircraft reaches a depth of approximately 13 ft. the pressure on the valve diaphragm moves the restraint on the firing pin, allowing it to descend under spring pressure and fire the cartridge in the head of each main air bottle.(c) Main air bottle
A main air bottle charged to a nominal 3000 PSI is behind each seat, integral wih the pressure sensing diaphragm assembly. Pipes from the assembly lead to the base of the ejection gun trip rod release unit. Bottle pressure is indicated on a gauge.(d) Ejection gun
Each ejection gun had a plug fitted to the lower end of the inner piston tube and held in position by two shear rivets. This reduces the volume of air required and also prevents the compressed air from bursting the diaphragm of the primary cartridge and possibly causing it to fire. A non-return valve is fitted into the base of each ejection gun to prevent any loss of cartridge gas into the uner-water escape system during normal ejection. In addition, a modified type of sear is fitted to the firing unit in the ejection gun breech, which allows the firing cable to dis-connect then the ejection gun extends, thus preventing the firing of the primary cartridge.(e) Rocket pack static line disconnect unit (Type 6MSA seat only)
Air from the main air bottle is also piped to the rocket pack static line disconnect unit, via the base of the ejection gun. On underwater ejection, the static line is disconnected, thus preventing firing of the rocket pack.(f) Auxiliary CO2 bottle and bladders
The Auxiliary CO2 bottle is on the starboard side of the seat, above the harness release leaver. When fired by rotation of the harness release leaver, gas is piped to two inflation bladders, one behind the parachute pack, and the other underneath the dinghy pack. The action of these bladders, on inflation, is to force the occupant forward and upwards.(g) Modified LSW
The LSW inflation bottle in the starboard side of the LSW is modified so that it is actuated by air from the main air bottle, via the drogue gun trip rod release unit and PEC. In addition it is increased in capacity from 34 to 86 grammes of CO2 to ensure correct LSW inflation when subjected to water pressure. To prevent a build-up of excessive internal presure, a pressure relief valve, set to 3 PSI, releases excess gas when on or near the surface. Manual operation of the LSW and the oral inflation facility are still available.(h) Modified PEC
The personal equipment connectors are modified to include the air line to the LSW inflation bottle and incorporaes a spring-loaded ball valve in the aircraft portion, held open when the seat and aircraft portions are connected and automatically closed to conserve the air when they separate.(j) Underwater escape selector handle
The underwater escape selector handle, to port of the seat, has two positions: SAFE and UNDERWATER. When SAFE is selected, the handle is in the up position and a slide valve is moved so that it blanks off the delivery ports to the base of the ejection gun and the drogue trip rod release unit. The same movement opens a port so that compressed air would exhaust outside the cockpit should the main air botte inadvertently discharge. Upon selection of UNDERWATER, by depressing the locking knob in the end of the handle and pushing the locking handle down, where it relocks, the slide valve is moved so that the vent to atmosphere is closed and the bottle contects, upon release, initiate the ejection sequence.(k) Manual firing handle
A manual firing handle is fitted to the staroard thigh guard. The action of pulling the handle up withdraws a sear from a breech unit mounted on the compressed air bottle diaphragm assembly. When the striker fires the cartridge, the gas pressure impinges on the valve diaphragm which removes the restraint on the main air bottle firing pin, thus initiating the escape sequence.15 Automatic underwater escape
When the sinking aircraft reaches a depth of approximately 13 feet the pressure on the valve diaphragm removes the restraint on the firing pin, allows it to descend under spring pressure and fires the cartridge in the head of the bottle. The compressed air is thus released and, on entering the bottom of the ejection gun, forces the piston tubes upwards, unlocking the seat and ejecting it from the aircraft without firing the ejection gun cartridges. At the same time air to the type 6MSA seat rocket pack static line disconnect unit operates the unit to disconnect the static line and prevent the rocket pack firing. The air to the drogue gun trip rod release unit forces a plunger out of its housing, and this releases the drogue gun trip rod, preventing the gun from being fired. At the same time the plunger strikes a linkage which withdraws the guillotine sear, thus severing the link line between the drogues and parachute. The movement of the plunger uncovers a port in the unit, allowing the air to proceed to the modified LSW inflation bottle, via the PEC. The bottle is thus actuated and the LSW inflated. As the seat rises on ejection, the time-release unit is tripped and runs for it's normal period of 1 1/4 seconds (1 1/2 seconds Type 6MSA seat), when the plunger descends and strikes the harness release lever. As the harness release lever rotates, it releases the harness locks and at the same time operates the auxiliary CO2 bottle which inflates the seat-man separation bladders. The occupant is thus forced from his seat, and is free to rise to the surface where he floats, supoprted by his LSW.