Abstract: An aircraft head-up display system has a combiner comprising a block of transparent glass and a plate of transparent glass cemented to the rear of the block. The plate carries a reflection holographic element on its front surface abutting the block. Light from a display on the screen of a cathode-ray tube is projected into the combiner through one edge, at an acute angle onto its front face. The light is then reflected rearwardly through the holographic element to the rear face of the plate where it is reflected forwardly again. The holographic element is arranged such that some of the light incident on it from the successive reflections within the combiner is reflected at right angles to the surface of the plate, forwardly through the front face of the combiner and into the line-of-sight of the observer. Successive reflections cause light to emerge at several locations along the length of the combiner so as thereby to increase the field of view of the system.