Rolls-Royce knew of engine fault but told Air NZ it was safe to fly, report says
The national carrier is working with engine manufacturer Rolls-Royce on an issue involving Trent 1000 engines.
Two Air New Zealand flights forced into emergency landings had known engine problems, but were deemed safe to fly according to the manufacturer's risk models.
In December 2017, an Air New Zealand Boeing 787 Dreamliner, bound for Tokyo, had to land suddenly after a failed engine caused the aircraft to shake violently with 282 people on board.
The following day another Dreamliner, this time bound for Buenos Aires, also had to turn back when similar problems arose after take off. Air New Zealand told Newsroom at the time that it was "extremely surprised by the two issues experienced".
Two Air New Zealand's Boeing 787 Dreamliner were grounded with failed engines in December 2017.
A subsequent inquiry by the New Zealand Transport Accident Investigation Commission (TAIC) found engine manufacturers Rolls-Royce knew of six in-flight incidents worldwide before the Air New Zealand incidents.
The TAIC interim report, published on Thursday, revealed the engine issues were caused by a known problem that happened earlier than predicted by Rolls-Royce's risk analysis model.
Damage to turbine blades on a Rolls Royce Trent 1000 engine shut down by pilots on an Air New Zealand Dreamliner just after takeoff from Auckland.
"The Commission's continuing inquiries into these incidents suggest that the failures were consistent with a known problem with unmodified Trent 1000 engines," said the Commission's manager of air investigations, Peter Williams.
"Rolls-Royce has been replacing engine components with a new design, and managing the safe operating life of unmodified engines using a risk analysis model.
"After the December incidents Rolls-Royce reduced the number of flights Air New Zealand could make under its risk analysis model, but obviously it would have been preferable that the model had taken the engines out of service before the December incidents could occur.
"After the December incidents Air New Zealand had also voluntarily reduced the maximum time to a diversion airport for which it would fly its aircraft with unmodified engines."
Since the Air New Zealand events, the European Aviation Safety Authority (EASA), which certifies the engines, also directed that aircraft should not be powered by two unmodified engines which had flown similar numbers of flights, he said.
"Since the Commission began consulting on a draft of today's interim report and associated draft urgent recommendations, further action by EASA and the United States Federal Aviation Authority meant final recommendations were not needed," Williams said.
The damaged blades are in the aft section of the turbine blade sections.
The report confirms that all eight incidents occurred during the take-off or climb phases of flight when engines are subjected to the highest stress, and the blade separations have followed cracking in the blade shank that has been initiated by corrosion.
Rolls Royce told the TAIC it is likely a combination of environmental and operational factors are involved and that they may be operator specific.
Rolls-Royce has been replacing blades in the Trent 1000 single-stage intermediate pressure turbine modules with redesigned blades made from a different alloy and with an improved corrosion protective coating.
It had been using a risk analysis model to determine how many flights unmodified engines may make safely.
Air New Zealand has been approached for comment.
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