The US FAA has finalised an airworthiness directive (AD) that will require operators of more than 500 Airbus A320 family aircraft to update critical avionics software related to the aircraft's traffic collision avoidance system (TCAS).

The estimated costs of the upgrade, which takes four hours to complete, is roughly $15,000 per aircraft.

FAA's decision to adopt the new rule is the result of two near mid-air collisions that occurred between A320 family aircraft, incidents that prompted the European Aviation Safety Agency (EASA) to issue an airworthiness directive on the TCAS alerting function in November 2008.

Investigators concluded that human factors issues related to the incidents, which involved resolution advisories issued by TCAS, included a lack of visibility of "relevant information" on the primary flight display regarding the flight control inputs necessary to avoid a collision.

"This condition, if not corrected, could result in erroneous interpretation of TCAS resolution advisories, leading to an increased risk of mid-air collision," says the FAA. The FAA rule is identical to the original directive issued by EASA.

FAA first proposed to mandate the software upgrade in July 2009, calling for changing out the Airbus electronic instrument system software with a new version that "consists of a change in the needle colour and thickness and an increase in the width of the TCAS green band".

The rule requires operators to change out the software, per a January 2008 Airbus mandatory service bulletin, within five years.

Source: Air Transport Intelligence news