The Ejection Site

F/A-18 Martin-Baker SJU-5/6A Seat

The seat shown here is a Martin-Baker Mk. 10US seat as fitted to the F/A-18. Many F/A-18s are also equipped with the SJU-17 NACES seat. In this case, the SJU-5/6A is the older style seat, but still a very good seat. The Mk. 10 is also used in many other aircraft including the Tornado IDS, and the Alpha Jet. The SJU-5/6A is also commonly used in experimental aircraft at NASA's Dryden Flight Research Center, where these photos are from.

The Timer Release Mechanism is very similar to the type used in the earlier versions of the Martin-Baker seats such as the Mk. H-7 seat used in the F-4 Phantom II. The main difference is in the way the TRM releases the scissors shackle. This photo of the headrest shows that the parachute box headrest has been placed on the seat, but not connected. The drogue shackle is visible with the blue nylon loop near, but not in, the scissors shackle connection in the center of the photo. The scissor shackle is somewhat different from prior versions as well. The dual gas lines to the catapult initiator are visible at the base of the picture. The catapult initiator is between the legs of the scissor shackle. The TRM connection is on the right hand side of the picture.

Since the parachute is not fully rigged, this picture shows the inertia reel strap fittings on the risers hanging loose. The SEWARS salt-water actuated releases on the Koch fittings are clearly visible. The SEWARS units are a prime part of the survival gear. In case of a water landing, the SEWARS would disengage the parachute risers by shattering the crosspiece under the nylon. This allows the parachute to drift away from the crewman and hopefully prevent it from either dragging the crewman or landing on the crewman and making it difficult for him/her to keep his/her head out of the water. The hook/loop fastener pads near the Koch fittings are used to hold the risers against the side of the headrest on the hook part of the pads which can be seen here just under the red "DANGER DO NOT PULL /// HANDLE". This is to allow the crew to enter the cockpit and strap in easier. Once seated in the cockpit, the leg restraints and risers would be connected as soon as possible to allow for a ground ejection in case of a problem on the flight line. Just under the headrest is the inertia reel unit, which unlike previous Martin-Baker systems is wider and mounted in front of the main beam assembly. Also visible is the composite back section which the padding is attached to. Nearer the top, the Drogue Gun Unit is visible, as well as the top latch wheel (golden star shaped unit) which is used to unlatch the seat from the catapult and allow the seat to be removed for maintainance.

The seat bucket contains most of the controls on the SJU-5/6A as well as the survival kit with the internal emergency oxygen system. As seen in this view, the seat safety control is at the front right of the bucket. The control is in the safe position. When it is tilted back into the armed position, the ARMED label would be visible to the crewman. Directly behind that is the manual separation handle (sometimes called the scramble handle). This is used to separate from the seat if there is a believe that the seat mechanisms had failed. Centrally located on the front of the bucket is the ejection initiation handle. This loop shaped handle is tilted forward in this photo so the top of the yellow and black stripes are visible. The clear plastic under it is the cover for the initiators. On the left thigh area there is a visible hole in the padding which is used to see the oxygen bottle guage in the survival kit. The hoses at the rear of the kit are for the emergency oxygen (right side of the kit {left in this picture}), and the REDAR hose and communications connection on the left side.

The leg restraint line snubber boxes are visible under the front protrusions of the survival kit. The blue nylon lines hanging down from the seat are attached at one end to the cockpit floor and fed through the snubbers then through the crewman's garters, and back to the snubber unit. On ejection, the lines are puilled throught the snubbers to hold the crewman's legs against the front of the bucket. The floor attach points have shear pins on them so that when the legs are in fully back, the lines are released from the cockpit. On seat separation, the snubbers are mechanically released.

The straps are the lap belt to the rear with the black adjusting boxes, and the survival kit straps with the green connectors forward of that. The green boxes connect to the crewman's harness at the hip. After seat separation, these straps hold the survival kit to the crewman as he/she decends under the parachute. These fittings are more typical of the USAF type seats. This seat from NASA is being modified to the NASA standard which uses the USAF PCU-15/P or PCU-16/P parachute harness with the F-16 ACES II type Frost riser connections on all their normal seats. This allows the crewman to use a single harness for several different type of aircraft. The riser fittings have not been changed yet on this seat.

On the other side of the bucket, the guarded switch raises or lowers the seat bucket on hte main beams for proper position in the cockpit. The mechanical lever just aft of that is used to lock or release the inertia reel straps, which like the shoulder belt in an automobile allow for leaning forward, but will lock under a decelleration load. The aircraft units also can be manually locked with this control. The inertia reel unit is visible just under the headrest in this picture.

Mounted below the seat bucket is the underseat rocket. Consisting of seventeen rocket proppellant tubes connected to a manifold which also has four nozzles and an initiator tube. In the accompianing photo, three of the nozzles are protected by ground safety caps. The one on the left of the photo is uncovered showing the press fit disk inside of the nozzle. As the pressure from the rocket tubes builds after initiation, these disks are forced out allowing the rocket exhaust to boost the seat clear of the aircraft.

Here are some additional photos
Left side Seat Bucket
Note the other SJU-5/6A back left and the F-15 ACES II to the right rear
Another view of the bucket
Left rocket attach point
Right rocket attach point
Seat in Cockpit Photos
Right Side,
note the trip-rod attached to the bulkhead,
and the rocket tubes under the seat bucket.
Left Side,
The trip-rod for the drogue gun unit is visible.
Also note the inertia reel unit from this angle.

Thanks to Nick Kiriokos for providing these photos.

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