Electronics and aircraft tracking

The missing Malaysian aircraft has, in some ways, highlighted the limitations of modern communications and the ability to keep track of all airliners during their scheduled flights. Today’s aircraft safety electronics are, without doubt, at the leading edge of technology, which only deepens the mystery of what happened to the Boeing 777 on its flight to China.

The complex electronics in a passenger aircraft can be broken down into roughly six areas: anti-collision, control, communications, monitoring, navigation and weather. Probably the oldest technology on board is radio, but even today’s modern units still have a limited range and even with satellite contact with the ground, it is patchy. However, VHF radio in AM mode is regularly used for aircraft to aircraft communications and for contact with airfield controllers. HF units can also be used on long flights and to link up with satellites.

For navigation, many aircraft use a VOR system (VHF omnidirectional radio range) that consists of a series of ground stations that send out an omnidirectional master signal and a very directional secondary signal, which are fed to a phased antenna that rotates in space 30 times a second. The signal phase is timed to vary as the second signal rotates. By comparing the two signals, the bearing of the aircraft can be calculated, which is then displayed in the flight deck.

Good as the VOR system is, GPS satellite navigation is taking over as being more accurate. The GPS sends several signals to the onboard receiver, one of them being from the satellite’s atomic clock. This signal, from several satellites, is measured, enabling the receiver to build a clock of its own. By comparing the two, and taking signals from several satellites, a form of triangulation positioning can be made. With just a few satellites, worldwide coverage can be achieved, which is why it is being adopted as the standard for in-flight navigation.

Radar has become very sophisticated, although only about 10% of the world is covered by radar. Again, satellites are providing tracking systems, including Doppler, that make it very difficult for an aircraft to get ‘lost’.

An autopilot is a well-known component of flying and is usually integrated into a flight management system that automates a wide range of tasks, particularly the management of the flight plan. This information comes from various sources including VOR, GPS and distance measuring equipment (DME) to ensure the plane’s precise position and course. Some aircraft carry traffic alert and collision avoidance systems (TCAS), but other aircraft must be fitted with an answering transponder for the radar to work. Ground proximity systems using a radar altimeter ensure the plane flies at a safe height and sometimes there is a digital terrain map to warn of high towers or mountains.

The flight recorder has become a vital device in determining the reasons for a crash or major accident. In addition to the more familiar flight data recorder and the cockpit voice recorder, some aircraft are fitted with a quick access recorder with its information stored on a removable medium. Special equipment is needed to read the data that is designed to attach to a desktop computer for easy access.

To survive crashes at sea, the two main recorders are fitted with locator beacons that are automatically switched on in a crash.  However, the beacon batteries have a working like of only 30 days.

One of the latest developments to ease crew fatigue is the ‘glass cockpit’, where the old analog display dials and toggle switches have been replaced with computer-like flat screens that show much of the information needed by a pilot on a routine flight. As a result, the LCD panels, some of them touch screens, are now the favoured method of showing flight information. They can display terrain, weather, approach charts and navigation images, and in most cases dispense with the traditional flight engineer crew member.

Transponders are devices that react to a radio interrogation. They help identify an aircraft on air traffic control radar. Although primary radar can track range and bearing, it cannot measure height. Secondary radar, via the transponder, can give pressure altitude identification for ground control.

ACARS (aircraft communication addressing and reporting system) is a digital installation that sends short messages between aircraft and ground stations using satellites. It is a system that will be gradually replaced by a new protocol for air traffic communications using the internet. On the aircraft is an avionics computer and on the ground a network of radio transceivers controlled by a computer that sends a data link message to airlines that are members of the network. Information such as engine performance can also be sent over the network and the system allows the crew to send and receive messages similar to email.

It has been suggested that ACARS could become an airline ‘black box’ to avoid loss of data when the conventional flight recorders cannot be salvaged after a crash. Unfortunately, a lot of bandwidth is needed for this system, which makes it expensive.

With all this electronics on board a modern airliner, flying has never been safer. However, accidents do happen, and with every incident meticulously investigated by specialist personnel, the cause or causes are usually found. In some cases it can takes years, as in the case of the Air France crash in 2009