The Transport Accident Investigation Commission (TAIC) says it is unsure how many planes are likely to be affected by a defective switch which caused an engine on an Air New Zealand Airbus A320 plane to shut down during a flight last year.
An inquiry into the incident which saw the flight from Wellington to Sydney make an unplanned landing in December 2024 has shown up to six instances where faulty or damaged fire switches caused A320 planes' engines to shut down unexpectedly.
Aircraft from the Airbus A320 family have been in the news recently after a global recall was sparked when it was revealed that intense solar radiation could corrupt elements of the planes' flight control systems.
The plane is the most popular single aisle commercial jet with over 11,500 sold to airlines around the world.
Pilots heard a loud clicking sound as engine lost power
On the afternoon of December 1, 2024, Air New Zealand Flight NZ249 departed Wellington with 154 passengers and crew on board heading for Sydney.
About 40 minutes into the flight the pilots heard a loud clicking sound coming from switch panels above and just behind their seats and instruments showed the number two engine was reducing its thrust.
The pilots carried out an engine shut down checklist before they declared a mayday and descended to an altitude the plane could maintain with only one engine.
Cabin crew and passengers were then informed the flight would divert Auckland where it landed safely.
The TAIC inquiry showed subsequent inspections of the plane revealed a fire switch for the aircraft's number two engine was protruding from the panel in its activated position.
Chief investigator of accidents Louise Cook said the switch was designed to shut down fuel supply to the engine and arm fire extinguisher systems in the event of an engine fire.
"The switch is part of a panel above and behind the heads of the pilot and co-pilot; neither had touched the switch, and post-shutdown procedures didn't tell them to check it," Cook said.
Multiple engine shutdowns attributed to faulty switch
The commission's report said weeks later a similar shut down happened where a fire switch popped out during a flight from Milan to Lisbon.
Enquiries with Airbus also revealed the company was aware of three similar occurrences with one dating as far back as 2016.
A common factor in the shutdowns was the presence of damage to the panel unit and a pin locking system in the affected fire switches.
Later inspections of the component on the Air New Zealand flight showed a guard over the switch and its mounting panel were deformed and a retention pin designed to keep the switch in place was out of shape and position.
Problems with the switches — believed to have been caused by mis-handling either during shipping or installation — had been identified earlier in the year.
Extent of the problem remains unknown
The switch's manufacturer had issued a pair of service bulletins ahead of the December flight relating to 125 panels — recommending they be removed from aircraft and sent for inspection.
They noted that the recommendation only applied to a percentage of panels which had been previously repaired and returned to operators and may have had external damage, but had not been assessed for damage to the switch internals.
Following the Air New Zealand incident, another plane experienced a similar problem but its component was not one of the group identified in the service bulletins.
Airbus subsequently issued service bulletins earlier this year covering all A320 aeroplanes where panels were showing signs of external damage.
The bulletins were classed as 'recommended' and to be completed with 1000 flight cycles of the bulletin being issued.
A later European Union Aviation Safety Agency Airworthiness directive issued last month stipulated that any panel where external damage was identified must be replaced with six months.
In February this year, the director of the Civil Aviation Authority of New Zealand pointed out to the European Union Aviation Safety Agency that the extent of the problem with the panels remained unknown.
The TAIC report noted that Air New Zealand had proactively removed affected fire panels and had advocated for clearer inspection criteria from the manufacturing and service agents behind the fire panels.
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