The pressure is on for operators in European airspace to comply with the latest mandatory requirement for air safety systems

Emma Kelly/LONDON


The safety of Europe's skies is set to improve further from 1 January, when the first phase of the continent's airborne collision avoidance system (ACAS II) mandate is due to be implemented.

From that date, all civil fixed-wing turbine-engined aircraft with a maximum take-off weight exceeding 15,000kg (33,000lb) or with more than 30 seats, operating in European Civil Aviation Conference (ECAC) airspace, must carry the latest Version 7 traffic collision and avoidance system (TCAS) equipment. Under the programme's second stage, aircraft exceeding 5,700kg or more than 19 seats must carry ACAS II equipment from 1 January, 2005.

In reality, operators have some breathing space - until 31 March 2001 - to meet the ACAS II mandate, because of the later-than-expected release of the technical standard order (TSO) by the US Federal Aviation Administration - in December 1998 - and subsequent problems with equipment availability, installation and certification. If operators are unable to have their aircraft equipped with Version 7 TCAS by 1 January, 2000 - and the vast majority of them won't - they can, under special conditions, apply for an exemption from Europe's ACAS II requirement.

ECAC airspace challenge

Until Version 7 equipment is available, operators are advised to fit its predecessor - Version 6.04a - and upgrade to Version 7 software during the transition. Operators can be exempted on the basis of, for example, late parts delivery, late approvals, unexpected technical or airframe installation problems or unavoidable delays to the certification process.

But it will still be a challenge to have the 5,000-plus aircraft operating in ECAC airspace equipped with the latest TCAS hardware by 31 March, 2001, concedes John Law, Eurocontrol's ACAS programme manager. Although Europe's ACAS mandate was issued in 1995, the late release of the FAA's TSO has made TCAS manufacturers' and operators' tasks more difficult.

ACAS II is an independent airborne system that interrogates the air traffic control transponders on nearby aircraft, tracks their flightpaths to determine whether they pose a collision threat, and computes resolution advisories (RAs) to indicate the vertical direction in which the aircraft should manoeuvre to avoid the threat.

Version 7 equipment, which is the only TCAS system to meet the International Civil Aviation Organisation's (ICAO) ACAS II standards and recommended practices (SARPs) and Europe's mandate, has only recently started to become available. AlliedSignal (now Honeywell) equipment has been available since August/September, Rockwell kit was approved in October and Honeywell equipment has only just received its TSO.

There is "a lot of pressure" to have the fleet equipped by the end of the implementation transition period, says Law. To help operators, Eurocontrol has set up an ACAS support unit as a focal point for any ACAS questions and to co-ordinate the ACAS exemption process. "There are very few Version 7 [TCAS systems] flying," says Law. "We are experiencing a very high level of exemption applications."

By early December, Eurocontrol's ACAS support unit had handled exemption requests from 400 operators, involving "a sizeable number of aircraft". Operators are required to say when they expect to have their fleet, airframe by airframe, equipped with Version 7 and keep to those dates.

The disturbing fact, however, is that despite all the publicity about the programme, a number of operators are only now beginning to contact TCAS vendors with a view to ordering equipment to meet the mandate. Law admits that Eurocontrol is "quite concerned" about this and urges operators to talk to their vendors now.

"This is a very challenging date [31 March, 2001] and it depends on everyone doing their job," he says.

Meeting operators' needs

Eurocontrol has talked to equipment vendors to ensure they can meet operators' needs. "They [equipment manufacturers] have assured us that they will have the production capability in time, but operators need to act early. There's no slack involved - the pressure is on."

Eurocontrol has also monitored operators' ability to meet the deadline. The percentage of the scheduled air transport fleet fitted with Version 6.04a TCAS is good - 60-70% - says Law, although the figures vary greatly in different European countries.

The Brussels-based air navigation organisation has also worked closely with the corporate aircraft community to ensure compatibility. "The European Business Aviation Association and the [US] National Business Aviation Association have been very helpful and supportive," says Law. "There is no overt hostility from business aircraft operators to the requirement. We are having a good response from business aircraft operators to the transition period exemption requirement."

Although Eurocontrol is aware of the problems faced by operators in meeting the ACAS II requirement, it stresses that the deadlines will remain and the programme will not slip because of a lack of compliance, as has been the case with earlier mandatory programmes. However, many industry observers believe that Europe will always face a problem with mandatory deadlines slipping because of the continent's lack of an enforcement body. The planned European notice of a proposed rule-making process is the only way to ensure that Europe's requirements are met, they believe.

The ACAS requirement is costly - about $150,000 per aircraft on average in equipment and installation costs - but the need for TCAS Version 7 in European airspace is clear. ECAC comprises a complex region in airspace terms - from light traffic in some areas to highly concentrated air traffic operations, and traffic levels constantly rise. As air traffic becomes more dense, the risk of mid-air collision increases. ACAS II could significantly reduce the risk of mid-air collision or near mid-air collision by at least a factor of two.

ACAS II is also necessary for the next stage in Europe's airspace restructuring - the implementation of reduced vertical separation minima (RVSM) in 2002. As vertical separation levels between aircraft are reduced, Version 7 will be an important safety net. Widescale Version 7 implementation is needed to reap early RVSM benefits across the continent. TCAS is a last-resort safety function to prevent mid-air collision when the primary means of separation has failed.

The Version 7 equipment about to be introduced in Europe is the result of many years of activity developing the optimum safety system. Twenty years ago, ICAO set up its Secondary Surveillance Radar Improvements and Collision Avoidance Systems panel to develop the ACAS SARPs.

Version 6.04a equipment has been fitted to more than 15,000 aircraft, but even that system, which the USA mandated in 1993, is not mature enough and not optimised for European airspace requirements. Analysis of more than 16,000 air traffic controller and pilot reports and 60 million-plus hours of operations of TCAS has resulted in the deficiencies of thesystem being carefully documented.

Version 7 equipment has resulted from a combined effort by ICAO, the FAA, Eurocontrol, the International Federation of Airline Pilots Associations, the International Federation of Air Traffic Controllers Associations, the Radio Technical Commission for Aeronautics and the civil aviation organisations of many countries. The equipment introduces more than 300 changes to Version 6.04a TCAS, including improved safety performance and operational acceptability, changes to the displays of traffic and alerts, logic performance and reduced radio frequency interference. Many of the improvements directly respond to the needs of the European airspace environment.

Resolving inconsistencies

Version 7 resolves inconsistencies in the logic of earlier software, improves safety performance and addresses operational acceptability concerns. The changes affect everything from surveillance and collision avoidance logic, to the display of alerts. RAs are simpler than before, with changes to the aurals and displays, and the vocabulary is more positive.

Extensive controller training continues throughout ECAC states to prepare air traffic controllers for Version 7 operations, and the Joint Aviation Authorities has issued comprehensive training material to help pilots cope with the transition.

Feedback from pilots and air traffic controllers was vital in developing Version 7 software and is just as important for future development of the system. A TCAS monitoring programme has been in operation since 1995/6 and is widespread across Europe. The programme tracks reports of TCAS encounters and analyses them from a safety, technical and operational viewpoint, says Law.

With the introduction of Version 7 equipment, a specific monitoring programme will be launched to provide early tracking of a certain number of Version 7-equipped aircraft, says Law. "It will confirm operationally whether it performs as expected," he says.

The additional monitoring programme will be a "sophisticated" one involving a "fair number of aircraft" of a group of airlines that has agreed to take part in the programme. This further monitoring will allow Eurocontrol to "react quickly to any unexpected issue that may arise", says Law.

Other regions are preparing for their own ACAS II implementation. Three ICAO regions - Europe, Africa/India and Asia Pacific - have made regional air navigation agreements on ACAS mandatory implementation. Also, ICAO's Annex 6 standard, adopted in November 1998, requires the mandatory carriage of ACAS II by January 2003. Yet other regions will be watching Europe's Version 7 experience closely as the world strives to improve airspace safety still further.

Source: Flight International