David Learmount/LONDON

THE UK IS TO BE the first European country to demand the use of traffic-alert and collision-avoidance systems (TCAS) in its own airspace. The UK Civil Aviation Authority says that it expects to give the go-ahead "within a matter of weeks".

The CAA says "Our research and operational studies show that TCAS II does provide a useful safety net against mid-air collisions. Under perfect conditions, TCAS II collision-avoidance logic can reduce the risk of collision by about eight times."

TCAS II is the version which provides the pilot with a "resolution advisory" [RA] instruction [action to take], as well as a relative traffic position/vector display.

An implementation date for UK TCAS is expected to be set at the same time as the go-ahead decision - making it the first Eurocontrol and European Civil Aviation Conference (ECAC) country to follow the US lead.

An Eurocontrol task force will report on the issue of general airborne collision-avoidance systems (ACAS), not necessarily TCAS, later this year. Its chairman, Richard Jenyns, says that early indications are that use of ACAS would improve safety.

Officially, the CAA says that, given the continuing work to improve the system, it hopes that Eurocontrol will sanction a TCAS II implementation policy for ECAC airspace.

The CAA study is continuing in conjunction with the UK Defence Research Agency, which has a BAC One-Eleven flying laboratory fitted with an AlliedSignal CAS-81 TCAS II. The CAA says that the intention is to work with the US Federal Aviation Administration and the avionics manufacturers to upgrade the US-mandated 604A software-standard TCAS II to a new level, known as version 7, by late 1997.

The improvements towards version 7, says AlliedSignal senior programme manager (TCAS) Tom Mullinix, will include:

introduction of a horizontal miss-distance filter to reduce conflict-alert warnings - the CAA says that, particularly with fast-moving aircraft such as military types, the RA can be triggered with traffic 5nm (9km) distant, and even with traffic diverging;

improvement to interference-limiting algorithms;

software logic extension to enable TCAS to cope with the situation where a pilot carries out evasive action contrary to the RA (it cannot now cope with this);

improvement to multiple-aircraft logic;

real-time RA downlink to air-traffic controllers, to pre-empt possible confusion over potentially conflicting advice from the ATC display short-term conflict-alert system.

Source: Flight International