PMD Film Transport Assembly

This Projected Map system predates the modern digital systems and uses 35mm film as the data store. The film is stored on spools mounted in a moveable carriage. A tungsten halogen lamp provides the light source to project the map image via an optical system on to a ground glass screen. A fresnel lens covering the screen gives even illumination and intensifies the image in the pilot’s field of view. The film strip is driven between the two spools at a rate proportional to the Easterly ground speed while the carriage holding the spools is driven in a perpendicular direction proportional to the Northerly ground speed. The map can be presented as North or Track oriented. The screen can be rotated and has a track arrow. The aircraft’s present position, track and track to the next waypoint can be presented. A film can cover an area of about 750 by 750 nautical miles with a Scale change for 1:250 000 or 1: 500 000. The PMD was used in the Jaguar Navigation and Weapon Aiming Sub-System NAVWASS. The Marconi Avionics system was replaced with TIALD from 1995