An investigation has found that aircraft engine manufacturer Rolls Royce moved quickly to address important safety issues that impacted Air New Zealand's new Dreamliner fleet.
A damaged engine of one of the aircraft affected by the design flaw. Photo: Supplied/Transport Accident Investigation Commission
Boeing 787 aircraft around the world with Rolls-Royce Trent 1000 engines were grounded when engine blades showed signs of corroding or cracking prematurely.
The Transport Accident Investigation Commission (TAIC) has resolved its inquiries into two incidents in December 2017 involving Rolls-Royce Trent 1000 engines on Air New Zealand Boeing 787s.
In one of the incidents, a blade from the engine was ejected when it broke, and struck the aircraft's tailplane, wing and fuselage.
On 5 December 2017, an Air NZ Boeing 787 was bound for Tokyo from Auckland when an engine started to reduce in speed. The crew checked and shut it down and returned to Auckland without further incident.
The next day another Air NZ Boeing 787 was bound for Buenos Aires from Auckland when readings showed an engine was "over temperature". That aircraft also returned to Auckland.
Taic said that in each incident, a turbine blade in the engine's intermediate-pressure turbine fractured and broke off due to corrosion fatigue cracking, caused by a combination of blade design or construction, engine operation and contaminants in the air.
On the Tokyo flight, the broken blade significantly damaged the engine and small pieces of ejected metal struck (without significantly damaging) the tailplane, wing and fuselage.
On the Buenos Aires flight the damage was mainly confined to the engine.
Taic said it was satisfied that Rolls-Royce had addressed salient safety issues identified in the commission's interim report in 2018.
Deputy chief commissioner Stephen Davies Howard said Rolls-Royce at the time was already replacing affected blades with a new design that used an established alloy with protective coating.
"The Commission resolved that further lines of inquiry would be unlikely to identify further circumstances with significant implications for transport safety; or to enable us to make further findings or recommendations for safer transport in future," Davies Howard said.
"The Commission's early investigations prompted Rolls-Royce to improve its system for forecasting when the fatigue might happen."
Rolls-Royce has now replaced the affected turbine blades in 99 per cent of the global fleet.