Airbus intends to secure certification this year for a modification that will eliminate the large number of false collision-avoidance warnings generated when aircraft are about to level off from a cleared climb.

Speaking at the Flight Safety Foundation European Aviation Safety Seminar in Istanbul, Airbus experimental test pilot Claude Lelaie revealed the airframer had developed a software modification for flight management systems that reduces vertical closure rate with the anticipated level-out altitude.

False warnings are caused when TCAS assumes a climbing aircraft will not level off but continue to climb into the path of another aircraft immediately above.

The TCAS in the higher aircraft makes the same assumption, leading both to generate resolution advisories that demand evasive action by the pilots. This problem has been exacerbated since the introduction of reduced vertical separation minima, which cut the separation distance between adjacent cruise altitudes to 1,000ft (300m).

Known as TCAS Alert Prevention, or TCAP, the Airbus system will eliminate many false resolution advisories. About 50% of such advisories, says Lelaie, are needlessly generated by aircraft approaching their level-off height.

He says the system is not intended to replace conventional altitude capture, but will "soften" arrival to an intended altitude only if TCAS detects proximate aircraft.

French investigators recommended development of such a system while investigating an airprox event in March 2003. The incident, involving an Air France A319 and A320, occurred at flight level 270 as the jets operated opposite-direction services between Paris and Marseilles.

Lelaie says that the patented system is being presented for certification on new aircraft, with approval possible as early as the end of this year. By 2013, he says, the company hopes to be able to offer it as a retrofit to all Airbus types.

This is the latest TCAS-related modification offered by Airbus which, in the past 18 months, has seen its autopilot-flown, flight-director guided resolution advisory system certificated.

Source: Flight International