The Ejection Site

Martin-Baker Ejection Details

Second Generation Seat Systems
The Martin-Baker seat system evolved one step at a time taking in one improvement at a time as each was brought to the attention of the designers. The early seats were designed to get the occupant out of the aircraft safely, and his (Sorry, ladies at that time period it was extremely rare for a woman to be a pilot...) return to earth was up to him. Obviously, in cases where the crewmember was injured or incapacitated, that would not do. In other cases, the crewmember might have ejected, and be found dead in his seat, with no apparent attempt to clear himself of the seat. A fully automatic system was developed to help reduce these situations. The engineering on the Martin-Baker seats was specifically designed to be reliable and positive. The diagrams on this page show a basic view of the main subassemblies of a second generation Martin-Baker seat such as the Mk. GRU-5 of the A-6A Intruder. The same basic functions were in use from the Mk. 3 thru the Mk. 8, including the Mk. GRU-7A used in the F-14, and the later A-6. The seat described here does not include a rocket assist as do the later marks. This means that for the crewmember to eject at low altitude, some forward motion is required to extend the ballistic arc far enough for the time delays described below to function. In the case of the Mk. GRU-5, a ground speed of 100 Kts on the runway would be sufficient for safe ejection. The diagrams are somewhat simplified to make the functions more clear.

Drogue Gun

The drogue gun was designed with a simple clockwork to fire after a second or two of delay from first seat motion to allow the seat to clear the structure and make sure the drogue could be launched into clear air. After that delay the drogue gun fires a slug of metal that weighs about one pound into the air with a cartridge similar to a 12 gauge blank. This physically, and violently rips the drogue chute from its pack in the headrest in front of the main beams. The drogue chute inflates rapidly and slows the seats forward motion, while stabilizing it vertically. Once the TRM functions (see below), the drogue shackle which is attatched to the drogue chute linesis freed and pulls the main chute extraction line. This line has attatchment points on both sides of the headrest which pull out a pair of clips (visible in the pictures of the TRM). These clips release the face curtain and the parachute box retaining lines. Then the chute extraction line pulls out the main chute rip cord pins allowing the pack opening spring to force the flaps of the parachute box open and launch the parachute out to inflate. The drag from the parachute overcomes the friction of the rest of the connections between the crewmember and the seat (all the 'hard' connections are released by the TRM as described below) and pulls the crewmember off the seat. Parts such as the parachute container box, the face curtain and overhead handle, and the parachute box retaining straps, as well as the seat itself continue on their merry way towards the ground.

Time Release Mechanism

The Time Release Mechanism (TRM) was designed to do several functions in two simple co-joined motions. It also functions with a basic clock mechanism that also has a short delay initiated by a trip rod attached to the cockpit bulkhead second delay in it. This timer can be delayed by two possible mechanisms. One is a simple weight and spring mechanism that prevents it from functioning while the seat is decellerating too rapidly. In other words in a high speed ejection the timer delays activation for a fraction of time while the seat slows slightly. Then the barostat inhibiter comes into play. The barostat is mounted on the side of the unit and by pressure differential determines if the seat is above a preset altitude such as 10000 feet. This is to prevent seat separation (and in the earlier seats- separation from the seat mounted Oxygen system) to allow the crewmember to descend to a warm, thicker atmosphere. Then the clockwork timer begins to tick. (Note: the animated GIF has a short delay imposed so that the drogue gun is fired first, then the TRM activates.) Upon its expiration, strong springs drive a rod in the downward direction. The top portion (black in the accompaning diagram above right) retracts to release a 'scissor shackle' which releases the drogue shackle and allows it to do its job. The lower end drives downward and releases by means of a torque tube the inertial reel harness. It also by a set of turnbuckle like links on the torque tube releases the seat kit and harness connections for the lap belt as well as the leg restraints.


The diagram on the left shows the basic function of the catapult and 80 foot per second gun. Catapult initiation is by pulling either the face curtain primary ejection handle, or the secondary ejection handle on the front center of the seat pan. Both handles on seats of this vintage cause the catapult sear to be withdrawn from the top of the catapult gun (which is also the mount that connects the seat to the cockpit. The catapult is bolted to the bulkhead of the cockpit and is made of three concentric tubes. The outer tube is outfitted with a set of rails which mate with six {three on each side} slides on the inner sides of the main beam assembly. The seat is fixed in place by the top latch which is the arrow shaped device on the top left side * of the main beam assembly. The top latch is equipped with an internal indicator which when the latch is set properly appears as a flush central dot on the outside of the top latch. The top latch must be seated firmly in place and all three surfaces {the top latch housing, the top latch, and the top latch indicator} being flush with each other for the seat to be safely in the aircraft). In this position, the top latch is inserted through the top latch window on the outer tube of the catapult assembly and into a 'V'-shaped groove in the breech assembly which is attatched to the innermost piston tube of the assembly. The cartridge in the breech at the top of the catapult then ignites and sends rapidly expanding gas (red) down the tube. When the gas pressure is enough, the inner and middle tubes are forced up the assembly by the pressure and jump over the spring mounted top latch. They then apply force to the main beam assembly and begin the movement of the seat up the rails. The beginning of the seat movement withdraws the sears from the TRM and Drogue Gun by trip rods that are mounted to the bulkhead of the cockpit.

Seals on the base of the middle tube prevent the gas from traveling up the area between the tubes. Once the middle tube has moved up the outer tube to the point where the 'pancake charge' (one of the mounts for the pancake charges is visible to the bottom rear of the picture of the TRM) or charges are uncovered. At that point the pancake charges are exposed to the hot gas and ignite. The gas produced (yellow) increases the pressure in the tubes and accellerates the telescoping of the tubes (and the speed of the seat itself). This is done this way to allow a higher speed on ejection without subjecting the seat occupant to excessive Gz. The staggered pulses of the charges therefore are less likely to cause injury to the pilots back (if he is seated properly. In later seats, the inertia reel attatched to the shoulder harness is powered by a cartridge and pulls the pilot upright prior to the seats initial movement.).

Once the middle tube is fully extended, a group of compression rings are crushed to slow it down and prevent it from continuing upward as the inner tube begins to extend. This tube is free to separate from the other two tubes and continues on with the seat. The seat/man package then continues as described above.

Leg Restraints

Mentioned earlier in passing was the leg restraint system. This consists of three major pieces:

  1. Leg Garters - Worn on the lower leg by the crewmember
  2. Restraint Lines - Routed from breakaway links on the cockpit floor via snubber units on the lower front of the seat bucket. From there they go through D-rings on the garters and back to latches on the seat front.
  3. Snubbers and Latches - lock the tightened restraint lines to the seat bucket and are released by the actions of the TRM
As the seat rises up the rails, the crewman's legs under acceleration naturally rotate about the knee to position the legs in front of the seat bucket On the continued ascent the leg restraint lines tighten holding the legs in this restrained position by means of a snubber unit which prevent the lines becoming slack. The pins in the breakaway links are sheared once the lines reach the full extent of their travel. The leg restraints keep the legs from flailing in the wind blast of a high speed ejection. When the TRM actuates the torque link in the seat bucket , the leg line release latches are operated, allowing the leg restraint cones to detach and the leg lines to slip free of the garters and let the crewman separate from the seat.

Manual Override

The Manual Override handle on the right hand side of the seat pan is used in two primary cases. The most common is in the case of an emergency evacuation of the cockpit. When the crewman is strapped to the seat by the lower restraint harness and the upper harness Koch fittings as well as the leg restraints it might take too much time to undo the connectors during a ground emergency. In that case, the crewman would squeeze the handle and raise it to the up and locked position. This accomplishes two things. First it mechanically (via linkages) releases the leg restraints, the survival kit, and the inertia reel. Second, but in the same motion, it withdraws the sear from the gullitine (yes, like the French gullitine) cartridge. This cartridge fires, and by means of a tube vectors hot, expanding gas up to a piston on the upper left side of the seat. This piston has a blade on it that cuts the parachute withdrawal line. The gullitine is the cylinder with the yellow guard over the cutting area forward of the drogue gun. The parachute withdrawal line is what connects the drogue shackle to the main parachute, and pulls it free during seat separation. Once these actions are complete (which takes little more than the time to raise that handle), the crewman stands up and exits the cockpit as rapidly as possible. Attatched to the crewman by his harness and the lap belt are the parachute box, and survival kit (undeployed). These would tend to limit the crewman's mobility slightly, but in an emergency situation would likely go virually unnoticed.

The second primary scenerio is if the crewman feels for any reason that the seat separation has failed to function, to provide a means for the crewman to manually separate from the seat and deploy his chute. This is accomplished as in the previous paragraph, except when the handle is lifted up, the crewman would push himself away from the seat structure, and pull the ripcord to actuate the secondary parachute deployment method. The parachute is normally pulled out of the pack by means of the drogue chute, which pulls the withdrawal line to release the ripcord pins, and then pulls the parachute in its deployment bag out until the chute lines stretch fully, where the drogue continues to pull the bag off the chute for a controlled deployment. In this case, the rip cord handle pulls the pack locking pins out, and the pack opening spring forces the pack flaps open. The opening spring pulls out a separate parachute drogue which deploys the parachute in the same fashion as the seat drogue, only with slightly less force.


The actions of an ejection seat are many and varied. In the Martin-Baker system described here the functions are mechanically activated, although some of them use cartridges to increase the reliability and force involved. The different devices are designed to operate individually and there is a manual backup system for the primary failure modes. Failures of either the drogue gun, or TRM can be handled by the manual separation mode, if the crewman acts in time. There is no substitution for a thourough understanding of all the parts of a seat and their intended function. In the rare case that you, the reader, would have to use one of these seats (and in saying rare, I include the crewmembers who fly planes with these seats), make sure you have understood the principles of the mechanics. These seats will save your life, if you give them the chance to. That means -

Note: The cutaway pictures of the top latch assembly were taken from the front of the seat, leading to them being backwards to the left-right reference. The reference of a seat is based upon sitting in it. The left of a seat would be at your left hand, and the right at your right.

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