The irony is woefully obvious. Aero engines developed for the newest generation of airliners are designed and built to be super fuel efficient, quiet and environmentally clean. But the Rolls-Royce Trent 1000, which powers around 45% of the worldwide Boeing 787 fleet, has been brought down, in part at least, by something as common as air pollution.

A large portion of Trent-powered 787s have been affected by the engine reliability issues.  Dozens of 787s have been parked airports around the world, their engines removed to be inspected and modified. Air China, Air New Zealand, British Airways and Virgin Atlantic are among those affected. Air New Zealand has suspended routes from its international network partly because of aircraft shortages caused by the issue after being forced to make significant schedule changes earlier to accommodate the inspections and repairs mandated for its 787-9s. Many other airlines are also experiencing schedule disruption because of the engine issues.

The baseline problem, Rolls discovered, was caused by “hot corrosion” in which the thermal barrier coating on the IP turbine blades was stripped away prematurely, exposing the underlying material to low cycle fatigue. Analysis of the phenomena indicated it was tied primarily to operations in and around airports in the Asia-Pacific region with high atmospheric sulfur concentrations. 

“It’s fundamentally pollution around big cities that have ‘dirty’ industries,” Rolls Large Engines chief engineer Frank Haselbach explained.

Adding to Rolls’ challenges, fatigue cracks were also discovered in the Trents, prompting an EASA engine-inspection directive issued in tandem with an aircraft-level FAA order limiting extended range twin engine operations (ETOPS) flights to 140 min. from the nearest suitable airport for certain aircraft, reduced from the 787’s normal 330 min. The order applied to Package C-powered aircraft with at least one engine having accumulated 300 or more cycles since new or the last IP compressor blade overhaul.

Rolls said in mid-September it was completing development of the final element of a suite of modifications to fix the issues and was confident the compressor blade redesign would be cleared for introduction in the next few months.

But the cost to Rolls and to its customers, the affected airlines, is in the multi-millions of dollars.  

None of Rolls’ engine manufacturer rivals (the GE GEnx is the alternative engine option for the 787) are crowing, however. Wherever you look in new aero-engine development, there are cases of in-service problems.

The other most notable problem has been the multiple in-service issues with the Pratt & Whitney PW1000G geared turbofan (GTF) that powers Airbus A320neos and A220s. This year, a problem surfaced with that engine’s knife edge seal. This impacted around 100 engines and cost Pratt some $50 million. The seal was introduced into new production engines in mid-2017 to eliminate an inspection requirement, but problems began to emerge within weeks of entry-into-service on new A320neos. Fractures caused rotor vibration and stalling in four engines, two of which resulted in inflight shutdowns and two in rejected takeoffs.

The incidents led Pratt and Airbus to issue urgent recommendations to affected A320neo operators to make sure aircraft had no more than one affected engine installed and banning ETOPS flights. By the time the problem became apparent, 43 engines had entered service on 32 aircraft.

Pratt and Rolls each identified the problems, found the fixes and have worked round the clock with their customers to get aircraft back in the air.

What seems to be happening is the engine manufacturers are being caught by problems in service that were not seen in development; even though they have all significantly increased the amount of development testing they do to ensure maturity at entry into service. The Trent corrosion issue is one that had not been seen before, presumably because the materials used are different, so it was not anticipated. 

The cracking issue also seems to show how even small changes in design can cause problems. In the GTF case, Pratt changed the knife seal—a seemingly miniscule component—and suddenly started seeing problems. 

It also seems that these new engines are so pushing the boundaries of technology, that the unforeseen becomes more probable. To be fair to the manufacturers, the airlines—and, indeed, the regulatory and national authorities—insist on higher and higher emissions standards coupled with better and better fuel efficiencies. So the engine manufacturers respond with technology. They say they will increase development testing even more for their next engines to ensure service entry mature, but it will be hard to guarantee there will be no new problems. 

After all, if polluted city air was not foreseen as a corrosion factor by engineers who specialize in designing eco-friendly aero-engines, what else is out there to surprise the industry? 

—Guy Norris and Graham Warwick contributed to this article.