Except during the unprecedented and temporary Covid19 situation, one of the most important goals of all air traffic control service providers is to increase airspace capacity to accommodate increasingly dense air traffic. There is a need to increase the capacity of individual airports and to take into account the growing number and operations of land mobile vehicles. Today, modern technologies for monitoring and controlling ground traffic are rapidly being introduced at large airports. One of the most serious safety risks at airports is the possible collision of ground mobile vehicles with taxiing, taking off or landing aircraft. Thanks to surveillance systems such as SQUID by the Czech company ERA, collisions can be effectively prevented.
In the past, even at large international airports it was quite common that the eyes of crews and drivers were the basic means of ensuring the safety of aircraft and ground mobile vehicles at airfields. Adherence to safe distances was based only on visual contact or visual observation by the aerodrome control tower. With reduced visibility, the movements of aircraft and vehicles were coordinated mainly by their own position reports.
During the early 1990s, the term Advanced Surface Movement Guidance and Control System (A-SMGCS) began to be used in civil aviation, where air traffic controllers could use the synthesis of information from several technologies simultaneously to create an accurate picture of the airport’s situation. Among the most important and now also very widespread technologies is multilateration, which is derived from Czech developed military passive surveillance systems and ADS-B systems (automatic dependent surveillance - broadcast). Most importantly for airport traffic management within the A-SMGCS concept is that multilateration and ADS-B make it possible to achieve significantly greater accuracy, reliability and durability than with secondary radars all at lower acquisition and operating costs.
SQUID beacons
Today, ERA’s SQB (Squitter Beacon) system, also known as SQUID, is one of the most widely used means for tracking and identifying mobile devices at airfields. Work on the SQB project began 15 years ago, at a time when many aspects related to ground monitoring at airports had not yet been firmly standardized. The main goal was to develop a simple, reliable and easy-to-operate device that would allow the A-SMGCS to display vehicles just like any aircraft. In other words, to develop a kind of vehicle transponder.
This has finally happened successfully and today SQUID is widespread at many major airports around the world. It is a compact beacon that in standard mode S transmits at a frequency of 1090 MHz a squitter, i.e. a standardized message containing the identification address and position information, vehicle identification, vehicle category and type code. The SQB obtains position information from its own GPS receiver, which, including its antenna, is integrated into one unit with the other components of the device. The beacon is protected by a cover and is designed to be able to operate in extreme climatic conditions at temperatures from -40 °C to + 70 °C and up to 100% relative humidity.
Around 2003, the first generation of SQUID was tested in cooperation with Prague Airport, which was then put into normal operation in 2004. A year later an improved version was available, in which the manufacturer achieved a further reduction; now one beacon weighs only 1.2 kg and is only 16cm high. It is attached to the vehicle using screws or a magnetic holder. Its big advantage is very low power consumption, which is less than 3 W, and it only minimally burdens the on-board electrical network and batteries of the vehicles on which it is located. It is possible to supply it by direct current with a voltage from 9 to 32 V.
However, the largest changes concern significantly wider user setting options. “While for the first SQUIDs the identification address was hard programmed and its change was possible only at the manufacturer, for the current beacons the address can be set by the user. They can also set other specific performance of the beacon, such as in which parts of the airport it should broadcast and in which not,” says the father of the SQUID, ERA developer Jaroslav Urban. It is possible to program, for example, an airport perimeter, areas not falling between movement areas, hangars and other places where it is not necessary to identify vehicles.
SQUID’s compact beacon is fitted to vehicles and transmits a squitter
A key feature of SQB is its seamless compatibility with all current multilateration or ADS-B technologies, including systems from other manufacturers. SQUID can thus be easily included as one of the elements of existing A-SMGCS airport systems. This is one of the key requirements for users of the beacons. The first was Prague Airport (they use 232 today), however in 2005 ERA was successful at Schiphol Airport in Amsterdam, the Netherlands, which is one of the European pioneers in the implementation of A-SMGCS. To date, 480 SQB beacons have been delivered there, making it the largest user of the system.
Other important users include Oslo (410 units), Berlin (402), Copenhagen (305 units), and outside Europe, Montreal (359), Kuala Lumpur, Malaysia (200 units) and Johannesburg (177 units). Hundreds more are in use at airports in places such as Turkey, Indonesia, New Zealand, Singapore. A total of 40 countries use the system. ERA’s most recent success was in Spring 2020, when it won a contract to supply 135 SQUIDs for Stuttgart Airport in Germany. The total number of SQUIDs produced and sold worldwide is almost 8,000.