Operators of Airbus A330s and A340s will have a four-month window to replace Thales Avionics pitot probes once Europe's safety regulator firms up the proposal for an airworthiness directive it published last week.

The European Aviation Safety Agency is inviting comment on its proposed mandated changes until 7 September. It has taken the action following several instances of aircraft suffering unreliable airspeed indications, and evidence of a similar situation before the loss of an Air France A330-200 over the South Atlantic on 1 June.

EASA had previously indicated that it intended to issue a directive requiring carriers to replace at least two Thales probes on A330/A340s with probes manufactured by Goodrich.

Its proposal says that occurrences of "airspeed indication discrepancies" have been reported during flights at high altitude in inclement weather conditions.

Investigations have indicated that aircraft with Thales pitot probes "appear to have a greater susceptibility" to the adverse conditions than those with Goodrich probes.

Thales developed a new probe, known as the "BA" type, to replace its older "AA" probes. EASA says the "BA" probe has improved airspeed indication behaviour on Airbus A320s, and is an option for A330/A340s.

But it states that this probe has "not yet demonstrated the same level of robustness to withstand high-altitude ice crystals" as the Goodrich "0851HL" probe. No other pitot probes are approved for the A330/A340.

EASA's directive will require operators with Thales-equipped A330/A340s to replace at least two of the probes - regardless of whether they are "AA" or "BA" - with Goodrich probes at positions 1 and 3.

If the carrier retains a Thales probe at position 2, says EASA, it must be the "BA" type. Operators can choose to replace all three Thales probes with Goodrich. The work must be completed within four months of the effective date of the directive, yet to be fixed.

EASA says the airworthiness directive is a "precautionary measure". Airspeed discrepancies could result in autothrust and autopilot disconnection, says EASA, and reversion to "alternate" flight-control law on the Airbus aircraft, as well as possible reduced control.

Source: Flight International