AVIONICS – A DIGITAL REVOLUTION

Date 14.6.2019

Avionics are without doubt the system which is undergoing the fastest evolution of all aeroplane parts. They have a key impact on plane efficiency, capabilities and safety, because they provide the interface for operating all systems, starting with flight controls, up to weapons and sensors, and therefore have always to be ahead of the development of other aeroplane systems. Currently, a new generation of advanced digital avionics systems is being introduced into service, with other improvements in the pipeline.

FLIGHT DATA ARE ESSENTIAL

Although the currently used MFDs in cockpits are far away from early 20thth century analogue gauges, their purpose has remained unchanged – to display information. Originally, until the middle of WWII, the purpose of all on-board instruments was to provide the pilot with information consisting of crucial flight data (speed, altitude, heading etc.) with the additional display of systems information as well (pressure and temperature of various systems). All those were needed for proper and safe performance of a flight, but the visual reference, when the pilot was looking out of the cockpit was still widely used. Later, the importance and precision of flight instrumentation increased as soon as the first all-weather planes capable of flights at night and in bad meteorological conditions started to enter service.

Additionally, the increased performance of planes also necessitated proper flight instrumentation as this helped to avoid dangerous areas of the flight envelope. With the post-war beginning of the jet era and rapid development of on-board sensors such as radars and guided missiles one more task appeared – the locating of targets and weapons guidance. At that time, analogue gauges were still used for flight instrumentation with simple CRT displays normally used for radar operation. Around the late 1950s the WWII-era collimator gunsight gives way to early Head Up Displays (HUD) presenting basic flight data.

With continuous evolution of the flight decks, pilots had more and more gauges available and the HUD allowed them to focus on the area in front of the plane with full control and awareness of the essential flight data viewed with special symbols on the HUD glass. In the 1960s the first multifunctional displays (MFD) also appeared in the cockpit, at that time still presented by CRT technology. There were several reasons for their introduction. Firstly, the amount of data needed to be presented grew significantly with more and more systems being introduced onto the plane. While a gauge can only display a limited amount of data, MFDs came with the paging concept where a single MFD was able to display several pages with different functionalities. Second, presentation through analogue gauges had technical limits and MFDs permitted the display of 3D data such as a digital moving map or a radar detection area. Additionally, MFDs allowed for simpler modification due to the fact only the processor generating the picture had to be updated or replaced in the event of aircraft systems modernization, while the gauge was normally replaced entirely.

With the development of silicon microprocessors and LCD technology in the 1980s, the first MFDs based on LCD displays with their own computer within the display appeared on the market (known as “smart displays”, because they are not working simply as a display, but technically represent a flight computer processing its own data based on aircraft data sources). Their processing capability allowed a further extension of their role and display capabilities. Originally, the majority of these “digital” display units were monochromatic, but full-colour variants soon appeared. Based on research in Europe, USA and the USSR the 4×4 inch display format was selected more or less as a standard, enabling easy-to-read data presentation. In the late 1990s larger displays appeared with some of 8×6 inch size almost doubling the originals.

NEW DISPLAY POSSIBILITIES

Since 2000 “glass cockpits” have become optional equipment for majority of planes with some planes offering it even as a standard. Their share of the market grew significantly, mostly due to lower implementation and updating costs, low maintenance requirements and high flexibility allowing wide customisation to customers´ specific needs. With the introduction of “glass cockpits” into regular service, new opportunities for further growth appeared and they had a heavy impact on which data are presented on the MFDs and how. While the early MFDs presented basically the same data as analogue gauges, new requirements and opportunities were possible after 2000 due to new warning and assistance flight systems available in the industry and new safety regulations requiring obligatory implementation of these.

Generally, the displays secure three fundamental functions – flight and aircraft control, navigation and communication with other functions as secondary, such as special systems management. Each of the functions’ associated data expanded, with probably the highest growth in the area of navigation. With new safety systems available, all aircraft OEM shifted to the increased “situational awareness” concept of the pilot as a way to improve flight safety.

While in 1980 the pilot needed to know his exact position and the position of the landing area, thirty years later the need to predictively display possible threats on route became standard. Such threats include everything from other planes in the area (so called TCAS systems – Traffic Collision Avoidance System), dangerous proximity to the ground (TAWS systems -Terrain Awareness and Warning System), dangerous meteorological conditions (weather radar) and other threats. Systems such as TAWS were later coupled with externally mounted IR and daylight cameras allowing overlay of the actual external situation picture with 3D database data. With the incredible growth of the special systems available, a new display system was needed in order to avoid crowding a pilot´s mind with too much information. This is how the first synthesised display systems appeared. These are focused on limiting the number of parameters displayed to the pilot while still heavily using all new systems. A typical example is advanced monitoring of the aircraft systems status, with the pilot being notified only of potentially non-standard values or values already exceeding the limits.

New systems and digital displays allowed the introduction of new navigation approaches such as systems called Highway in the Sky, presenting the flight path in a new way, allowing easy correction of directional or altitude deviations. Also, the new large and full-colour MFDs allowed easy presentation of digital display maps where pilots can actually see a 3D model of the terrain. The peak of navigation systems is today represented by the synthetic vision systems combining data from various databases and sensors. Those systems are designed for daylight use as well, but are found to be extremely useful especially during bad weather and night flights.

With the 3D terrain map they allow the pilot to see on an MFD or HUD the complete landscape of the area of operation, even though there is no natural visibility from the cockpit, with highlighting of all threats such as power lines and masts, mountain and hill tops or other aircraft in the area. Improvements in satellite-based navigation should be mentioned as a part of the developments in navigation systems. Several new concepts such as WAAS (Wide Area Augmentation System) permitting an increase in GPS precision were introduced into regular service.

SPECIAL MILITARY LINE 

The leading role in avionics development was for a long time with the military. In addition to the improvements mentioned above these required additional features. One typical example of combined increased situational awareness and mission systems engagement are Helmet Mounted Displays (HMD). Although the “glass cockpit” with HUD allowed perfect data presentation, for fighter and attack aircraft it was still not enough. Their pilots were tasked to focus on the enemy position even during manoeuvers, which is hard to do when the pilot is watching the instrument panel in the cockpit and both one’s own and the enemy plane are moving. In order to combine continuous situational awareness with freedom of head movement, the new system called HMD was introduced. While the HUD is limited by the direct line of sight of the pilot, HMD may be a monocular or binocular system attached to the pilot´s helmet allowing the pilot to still see flight data regardless of head position and eyesight direction. Obviously, such a capability for military planes was connected with weapons-aiming capability.

HMD has become standard for fighters since 2000. Another typical military feature are night vision goggles allowing area observation even at night. They are based on the amplification of ambient starlight, moonlight or other light at night and normally represent by a binocular attached to the flight helmet. Today, the latest systems are using digitally processed picture presented on the helmet windshield using data from helmet-mounted night and IR light sensitive cameras. Connection of the helmet and externally mounted cameras allows the pilot to see “through the aircraft” and view, for the first time, areas of limited visibility. Also, MFDs have undergone significant development in the past few years. From separate MFDs, a new concept of “Large Area Displays” (LAD) is used on the latest military planes.

It normally presents the data as before, but on a large area display occupying the whole instrument board area. Unlike the MFD with its bezel buttons, LADs are typically touch screen operated and allow wide customisation of the visible data scheme. Voice control of non-core functions is also starting to appear in most modern planes. A special line of avionics development may be seen in helicopters. Due to their capability to land away from airports in areas with no ground navigational aids, they have to deal with extra situations such as landing in dusty areas. This is why various sensors from IR cameras up to microwave radar sensors are used for continuous information about the area of operation. Civilian and also military helicopters also use laser detection of obstacles on the flight path such as power lines. In parallel with historical development, civilian planes are widely starting to use originally military features and for example even passenger planes are starting to be equipped with HUDs and LADs. For example, the Boeing B787 Dreamliner uses four large MFD displays with two HUD displays as the basic flight instrumentation.

IN CONCLUSION

Avionics systems have been undergoing continuous evolution for more than a century. While the flight performance of aircraft has reached limits in some areas and just minor changes may be introduced into service, avionics are surely the part of each aircraft which has undergone the largest change. Although it seems the LADs, HMDs and other systems are the most modern devices available, engineers are facing new challenges. New concepts such as Virtual and Augmented Reality are under evaluation. They provide advanced overlay and synthetics of the natural picture with synthetic digital data. For example, the Bell FCX-001 next-generation helicopter technology demonstrator lacks the “standard” instrument board and comes with all displays in 3D glasses only. With the increased importance of virtual reality in other areas of industry and in life in general, it is more than certain that this is the future of avionics.

Text: Jakub Fojtík

Photo: author, Rockwell Collins, Garmin, Bell Helicopter Textron

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