The upgrade of existing seats has been documented in other places in a superficial way. What exactly was done to the Mk 4 and Mk 5 seats to bring them to the new Mk 6 and Mk 7 standard seats respectively?

Lets look at one example in detail and follow the process of an upgrade.

The original Dassault Mirage was fitted with the best seat of its time, the Martin Baker Mk 4. This was the first of the new generation "lightweight" seats and was very capable compared to earlier seats.

However it did have some shortcomings:

In 1961, Martin Baker had proved that a rocket assisted zero / zero ejection was practical and later seats went on to combine the successful gun / rocket system still in use today.

 They went on to design and manufacture a modification kits to retrofit to existing Mk 4 and Mk 5 seats to bring them up to the new standard. Many Air forces who used the Mirage adopted the modification and the system has been proved many times since.


Apart from fitting a rocket pack!

The brown shaded parts show the new or modified components:


Martin Baker introduced what it Called the "Principle Modification Items" and was dominated by the rocket pack component element of the project. However the remaining components had a very important part to play in the success of the modification programme.

 The rocket pack consisted of a central manifold to which were attached a number of tubes containing the propellant type KU.

Also attached to the manifold was a tube containing a gas pressure fired firing pin assembly and cartridge to ignite the propellant. There were four efflux nozzles.

The whole pack was fitted to the seat pan of the seat by two mounting bolts and a rigid arm protruded from the rear of the rocket pack and located into a track attached to the main beam of the seat. The angle between the track and the seat pan runners was divergent which resulted in the alteration of the rocket pack as the seat was adjusted. In this way the thrust of the rocket is automatically adjusted to compensate for the centre of gravity shift which occurred as the seat pan was adjusted. Later seats utilised a manual "dial in weight" system that adjusted the thrust through the whole mass of the ejected package.

The rocket motor was fired by the action of the Rocket motor initiator which was fired after the seat had travelled 71 inches from its installed position.

 A coiled static line is stowed in the breech mechanism (see drawing on right) situated near the top of the port side of the main beam. The free end of the line is attached to the drogue gun trip rod.

As the seat moves up the rail during ejection the coiled static line is paid out until it becomes taut at the end of 71 inches of travel. It then pulls out the sear, fires a cartridge and the gas travels down a tube to the rocket firing mechanism under the seat. The gas pressure actuates a firing pin which fires a cartridge that ignites a rocket initiator charge and in turn ignites the rocket propellant instantaneously.


In order to accommodate changes in the system so far the following modifications to the parachute assembly were also introduced:


Other modifications were introduced to bring the older seats up to a new standard. These comprised of the following: