The Australian Travel Safety Bureau (ATSB) has released its comprehensive report into an Airbus A320 mishap, prompting an “anticipated” global software retrofit.
The report was stirred by an investigation into the unexpected disconnection of an Airbus A320’s auto-pilot and auto-thrust, on board Virgin Australia Regional Airlines flight VA9053 in 2015, which resulted in a string of safety alerts triggering in detection of several problems on board the flight.
However, a fault caused by erroneous airspeed readings, which occurred as a result of blocked drains in pitot probes—an instrument used to measure air flow in pipes—, was removed from the pilots’ safety alerts screen during the incident, the ATSB report shows.
Following the incident, the flight crew continued their ascent to 20,000 ft, where they levelled out to troubleshoot the issue, before returning to Perth.
“During the approach, when the flight crew were aligning the aircraft with the instrument landing system, they received a stall warning,” the report states.
The warning stopped after six seconds and the approach continued, with the aircraft landing safely back in Perth. The investigation has been ongoing since September 2015, when the incident occurred.
At the time it was not immediately clear what caused the auto-pilot and auto-thrust to disconnect at 8,500 ft during the plane’s ascent, due to the ship’s onboard Electronic Centralised Aircraft Monitor (ECAM) prioritising engine-related faults—including angle-of-attack—during the flight.
ATSB has stated the more immediate danger was the unreliable airspeed associated with the disconnection of auto-pilot on board the A320, which should have been prioritised by the aircraft’s ECAM system.
“[T]he NAV ADR DISAGREE alert was not immediately visible to the flight crew due to the limited space available on the ECAM display,” the report states.
In August last year Airbus informed the ATSB that it would proactively roll out several modifications to its flight warning system to address the issue, which are currently planned for 2019, the report states.
Following these modifications, which will include a re-prioritisation of Airbus’ NAV ADR DISAGREE alert—an alert relating to unreliable air speeds—Airbus will conduct a “worldwide retrofit” of related flight software.
The retrofit of related flight software is to ensure that in the event of a similar scenario, a NAV ADR DISAGREE alert would be directly visible to flight crew.