Japanese airline group ANA Holdings, Inc. (Tokyo, Japan) is cancelling flights as it checks for corrosion in the Rolls-Royce engines on a number of its Boeing 787 aircraft. The airliner has experienced two cases this year in which aircraft had to return to their departure airports due to engine-related irregularities.
As a result, ANA has been working with Rolls-Royce, the designer and manufacturer of the engines in question, to implement technical solutions. According to analyses by Rolls-Royce, the issue was determined to be fatigue cracks in the blades of the engine’s intermediate pressure turbine.
Such cracks are the result of sulfidation corrosion caused by chemical components in the atmosphere, and the propagation of these cracks correlates with the number of flight cycles that an engine has been used for, ANA says.
Aircraft operating on international routes typically fly through airspace which has higher atmospheric concentrations of the chemical components, and their engines also produce higher temperature exhaust gases due to greater power output. These factors were determined to be more likely to generate fatigue cracks.
As a result, ANA implemented a program earlier this year to determine the number of flight cycles at which intermediate pressure turbine blade cracks could occur, based on analysis of each engine’s flight environment and flight cycle count. Accordingly, ANA says engines are being systematically replaced before that number of flight cycles is reached.
Meanwhile, aircraft operating on domestic routes within Japan fly through airspace with lower atmospheric concentrations of the chemical components in question. Additionally, their engines also have a lower power output.
Therefore, it was determined that fatigue cracks due to sulfidation corrosion were less likely to occur on domestic airliners, and these engines will not be subject to systematic replacement, ANA says.
However, the same issue occurred on a recent ANA domestic flight on August 20. Therefore, the airliner says it decided to replace the engines on aircraft used for domestic operations earlier than what was designated by Rolls-Royce. This led to a temporary reduction in available aircraft, which spurred flight cancellations.
“Going forward, we will be replacing the engines with new ones which are equipped with improved, corrosion-resistant turbine blades as a permanent solution,” ANA says in a statement.
“As a measure to prevent the occurrence of cracks until this solution is fully implemented, engines which have been removed from aircraft will be fitted with brand new or minimally-used turbine blades of the type that is currently in use,” the company says.