The Heads Up Display [HUD] is an avionic display system that allows certain flight, weapon, and targeting information to be presented to the pilot at eye level. This allows the pilot to view the information while still observing his surroundings. This is in contrast to the conventional instrumentation package that requires the pilot to look away from the cockpit windows and down at the instrument cluster. The first HUD was installed in the 1950’s. It was developed from the reflective gunsight technology that had been implemented on fighters in the Second World War.
This sight used a generated aiming sight reflected off a glass pane. The projector was mounted on top of the instrument panel, so that the generated image was in the pilot’s field of view. The sight was not automated; the pilot was required to calibrate the instrument each time a different type of aircraft was engaged (Ingman 2005, p. 7). The reflected gunsight was replaced by the Cathode Ray Tube (CRT) in the late 1950’s. This implementation utilized computer technology to control the sight.
The programming automatically compensated for bullet drop, speed, range, and other factors. This marked not only the birth off the modern HUD, but also the beginning of airborne computers in the cockpits of aircraft (Ingman 2005, p. 8). Flight data was added to the HUD in the 1960’s. This data not only assisted the pilot in combat, but also on landings. The essential flight data was displayed such that the pilot was no longer required to look down at his instruments during the landing cycle (Ingman 2005, p. 10). Civil aviation was slower to utilize the technology.
The first commercial HUD was developed during the 1980’s. Air Inter (later absorbed by Air France) installed HUDs on their MD-80 Aircraft. These units simply repeated data and information from the aircraft’s other HEADS UP DISPLAY IN AVIATION PAGE 2 of 10 instrumentation. Rockwell developed the first standalone HUD in 1984. The unit was named the “Head Up Guidance System [HGS]”. This unit allowed reduction in the takeoff and landing minimums (Ingman 2005, p. 8). The HUD system consists of several major components.
The computer receives data from the flight sensors and provides information to the projection unit. The projection unit projects this information onto a glass screen in the pilot’s field of view. The unit is controlled by the HUD control panel (Civil Aviation Safety Authority [CASA] 2004, p. 6. 21-1). The computer consists of two subsystems, the processing unit and the symbol generator. In addition, there is a complete redundant system that checks for failures. This system consists of a duplicate set of sensors, a parallel computer, and a system status monitor (Ingman 2005, p.10).
The dataset the computer receives comes from a variety of sensors. The Inertial Reference System provides x,y, an z positions, velocities, and accelerations. The Air Data Computer inputs airspeed, vertical speed, and barometric altitude. The radar altimeter provides the altitude above the terrain. The gyroscope set sends pitch, yaw, and roll. The navigation radios give bearing, distance, glide slope deviation, and course deviation (Ingman 2005, p. 10). The computer also takes input from the HUD control panel (CASA 2004, p. 6.
21-1), as well as from FLIR and other imaging cameras (European Aeronautic Defense and Space Company [EADS] 2005, p. 16). On military aircraft, the HUD computer also receives targeting data from the aircraft’s RADAR, Infrared [IR], and other sensors. Weapon status is received from sensors in the weapons themselves and on the mounts (Federation of American Scientists [FAS] 2000, p. 1). HEADS UP DISPLAY IN AVIATION PAGE 3 of 10 The computer translates the flight and combat data into flight path, altitude, attitude, pitch, heading, and airspeed.
This information is processed by the computer’s symbol generator, which creates the symbols that the display generator will process (Ingman 2005, p. 10). They are designed to be intuitive symbols that the pilot will be able to process without being distracted (EADS 2005, p. 16). This information is then sent to the display unit (Ingman 2005, p. 10). A duplicate dataset is sent from the HUD computer to the system status monitor. This data is compared with the dataset the parallel computer generated.
If there is a discrepancy, then warning messages are sent to the display unit (Ingman 2005, p. 10). The display unit consists of a cathode ray tube [CRT] and a combining glass. There are two basic types of HUD display units. In the refractive HUD, the [CRT] is normally mounted in the panel facing up. The image is passed through a collimating lens, which splits the beams. The images are reflected on the glass toward the pilot. These images are combined at the glass with outside light. This design allows the pilot to view the images from any angle (Ingman 2005, p. 9).