The Head-up Display presents flight information to the pilot by projecting an image onto a semitransparent sheet of glass in front of the pilot, called the Combiner. The HUD projector is installed above the pilot's head and includes an image source that displays the green symbology and EVS video, if selected.

Lenses in the overhead unit are used to project the image onto the HUD Combiner that is precisely located to reflect the image into the pilot's eyes. Because the Combiner is designed to only reflect the specific color of light projected by the image source, the pilot is able to see the projected HUD image overlaid on the outside world without any noticeable distortion. The Combiner is also a collimator that makes the projected image appear to come from optical infinity - the same as the outside world - so the pilot does not need to refocus their eyes to see the symbology. The projector is connected to the HGS Computer that calculates and draws the symbology on the image source.

The HGS Computer

The HGS computer is what distinguishes the Rockwell Collins Head-up guidance System from a simple HUD. Based on inputs of the essential flight data from the aircraft systems, the computer claculates the precision guidance and flight path information and sends it to the overhead unit for projection on the combiner for the pilots. The computer can also accept video signals from enhanced vision sensors or synthetic vision generators and combine it with the symbology for display. The computer is a standard 6 MCU size.

The overhead unit

The overhead unit, or HUD Projection Unit (HPU), is installed above the pilot's head in the flight deck. It projects flight information and EVS video onto the combiner. The overhead unit includes an image source (either a CRT or an LCD) with the electronics to drive it, and a set of lenses.

The combiner

The combiner is installed in front of the pliot, attached to the structure above the windshield. The combiner can be tucked away when not in use by releasing a catch and stowing it like the sunvisor in a car. The combiner glass in transparent, but has a special coating that reflects the green image projected by the overhead unit. Knobs on the combiner mount allow the pilot to control the brightness and contrast of the images.

The control panel

On some aircraft, a dedicated control panel is installed that allows the pilot to monitor HUD status - and to enter parameters used by the system. If a Multipurpose Control Display Unit (MCDU) or equivalent is installed on the aircraft, the HGS can be configured to use the existing unit. If the HGS is fully integrated into the flight deck, then all interaction with the pilot can be through the central control interface.