Airbus is investigating further uncommanded altitude changes on A350 twinjets despite modifications implemented after a similar situation emerged on the type two years ago.
A350 crews had previously been given a revised altitude-selection procedure after investigations found that a failure of the altitude-selector dial – located on the flight control unit – could result in changes to the target altitude.
This target could change by 100ft or 1,000ft, depending on the interval setting, and lead to unexpected deviation from the intended vertical trajectory.
The European Union Aviation Safety Agency stated in 2021 that incidents of unwanted altitude changes by the auto-flight system had been traced to a manufacturing flaw on the altitude-selector knob’s encoder.
Airbus developed a new flight-control unit standard – known as H6.0 – which enabled operators to withdraw the amended altitude-selection procedure on updated aircraft.
But EASA has newly disclosed that “several operators” have reported uncommanded altitude changes on aircraft which have undergone the modification.
“Airbus is investigating the cause of these reported events,” says the regulator.
It states that the temporary procedure revision for altitude selection is being reinstated, to cover all A350-900s and -1000s – including those with the updated flight-control unit – as a precautionary measure.
EASA says its directive is an interim step and it could instruct operators to take further action.
