iscover
Australia acquired 19 Thomson-CSF Monopulse Secondary Surveillance Radars (MSSR) as part of the radar replacement programme. These model RSM 970 sensors are all Mode S capable although there are no immediate plans to introduce the technology into Australian skies just yet. In terminal areas such as at Brisbane airport (shown here), the radar is mounted atop the TA10 primary radars. In other areas the MSSRs are used on their own as enroute sensors and provide seamless radar coverage from the Great Australian Bight around the entire east coast to near the top of Cape York.
Airspace Management
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Tcas Recommended
Our Airspace Management column, “Who is in Control?” (AA April 95) discussed the use of Traffic Alert and Collision Avoidance Systems (TCAS). In that article, we reported that the then CAA had no plans to make the carriage of TCAS mandatory. That looks likely to change following interim recommendations of a Bureau of Air Safety (BASI) report. The interim recommendation follows the ongoing investigation into an airmiss which occurred earlier this year between a British Airways 747 and a Qantas 737. In short, the 747 was TCAS equipped and its crew took avoiding action to avert what may have been a very serious risk of collision. The report said: “Between January 1 1993 and September 19 1994, there were 47 reported airmiss occurrences involving two or more RPT aircraft. In addition, between September 19 1994 and May 25 1995, there have been 47 occurrences in controlled airspace where a breakdown of separation standards involving aircraft not equipped with TCAS occurred, and 10 cases where TCAS activated and assisted crews in their decision making process. Furthermore, Bureau records indicate 29 occurrences outside controlled airspace (OCTA) where an Airborne Collision Avoidance System (ACAS) would have assisted in situations where two aircraft came into conflict.” As reported in this column in April, the US FAA has mandated the fitment of TCAS to all aircraft with 10 seats or more, and the UK CAA is close to a similar ruling. The fitment of a TCAS derivative, Traffic and Collision Alert Device (TCAD) in some Australian GA aircraft has led to three alert situations OCTA. In two of these cases the other aircraft was sighted and avoiding action was taken. In all these cases the installation of TCAD improved the options of the pilots and gave them timely advice for avoiding a potential airmiss. The BASI interim recommendation concluded: “The Bureau believes that there is sufficient evidence to justify the introduction of ACAS equipment in RPT operations at the earliest possible opportunity, and for it to be fitted at a later date to other aircraft engaged in the carriage of passengers for hire or reward.” Meanwhile, Qantas has announced it will spend about $10 million fitting TCAS to its domestic jet fleet following the recommendations of its own safety department. The system will be fitted to some 40 Boeing 737s and Airbus A300s. TCAS is already fitted to the Qantas international fleet to satisfy the requirements of other countries where TCAS is, or will be, mandatory. Ansett are doing likewise.
What Is Mode S?
Mode S, or Mode Select, is an advanced radar interrogation system. It can interrogate aircraft on a selective basis, and permits a two-way data transmission between the ground station and the air. It achieves greater accuracy in dense traffic compared with conventional secondary radar, as the selective function avoids interference from closely spaced aircraft. It is expected to increase ATC capacity and accommodate traffic growth projected in the next 25 years. A unique feature of the Mode S signal is its expanded address capacity. Instead of today’s limit of 4096 aircraft codes, Mode S can assign a code for up to 16 million aircraft. While used primarily to ascertain aircraft identification and altitude, the Mode S datalink between the ground and the air can also transmit other data such as a flight plan, weather, maintenance and similar information. Mode S operates with aircraft equipped with a Mode S transponder. ICAO guidelines require all new aircraft to be equipped with Mode S transponders and programmes in the US and Europe have seen widespread implementation. However, elsewhere the transition is slow. So slow in fact, that in regions where traffic density is not an issue, it is possible that satellite surveillance systems may be in place before secondary surveillance radar and Mode S enhancement. Progress is regional; for example the mandatory collision avoidance equipment TCAS, introduced in the US this year (see above) is Mode S compatible. In western Europe, Mode S transponders are now carried on over 60 per cent of commercial flights.
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