Aviation Week’s Commercial Fleet & MRO Forecast estimates that airlines will spend $33.7 billion, at 2018 price levels, to maintain GE90 engines through 2027. Nearly 30% of demand is from the Middle East, while another 25% comes from the Asia-Pacific region.
Western Europe and North America account for the next-largest outlays for the engine type, with $5.9 billion and $3.7 billion, respectively. China, at $2.7 billion, Africa at $1 billion, India at a little over $600 million and Latin America at nearly $500 million account for the rest.
Demand from the Middle East and Asia reflects the GE90’s role in powering Boeing 777s, which are heavily flown, long-haul workhorses. Average utilization for GE90-equipped aircraft will average 4,717 hr. annually through 2027, or nearly 13 hr. a day.
The total engine count is fairly stable. About 2,500 GE90s are in service. This number should remain roughly constant through 2021, then ease slightly to about 2,400 in 2027. MRO spending will increase with age, starting at $2.5 billion this year and rising to $3.7 billion in 2023.
The mix of types shifts significantly over the 2018-27 period. Newer GE90-100-series engines represent 86% of in-service engines in 2018, rising to 95% by 2027. The number of earlier GE90-76Bs, 77Bs, -85Bs, -90Bs and -94Bs will decline.
Reliability for both older and 100-series GE90s has been 99.9%. Jean-Louis Forest, vice president for engine services at Air France-KLM Engineering & Maintenance (AFI-KLM E&M), says performance retention, inflight shutdowns, delays and cancellations for both -100s and earlier GE90s has been “satisfactory.” For a mature engine, it has few service issues.
The FAA has issued 21 airworthiness directives for GE90s since they entered service in 1995, on average about one per year. Three were issued in 2017, involving compressors and oil coolers.
Early GE90s do have problems with high-pressure compressor distress and tip curl, due to ice-crystal ingestion. AFI-KLM E&M’s monitoring and GE’s remote diagnostics can detect possible tip curl and initiate on-wing fixes.
Another issue is low-pressure turbine 6 (LPT6) blade inspection and replacement. AFI-KLM E&M prevents disruptions by setting inspection limits for LPT6 quick turns on-wing.
Oil consumption and carbon-seal leakage can also be problems. The MRO provider monitors oil consumption and schedules fault-isolation manual tasks on time, rather than using GE’s new carbon seal.
GE90s typically stay on wing 30,000-35,000 flight hours, or 3,500-4,500 flight cycles between performance restoration visits. Earlier GE90s are approaching their third visit and the -100 series its second.
AFI-KLM E&M supports GE90s for its parent carriers and dozens of other airlines. Overhauls also can be done at GE’s Wales facility and MROs at Taikoo Engine Services (Xiamen), Emirates, Air India and Japan Airlines. Last year, GE and Singapore Airlines announced plans to form a joint venture in Singapore to overhaul GE90s and GE9Xs.
Typical shop visits restore performance for a full run, as the high-pressure turbine receives performance restoration. Other modules receive work depending on inspection and the work-scope planning guide. High-pressure compressors should generally be exposed every two visits. The -100 series has a disassembly procedure that limits hardware exposure and work-scope creep. Earlier GE90s do not, so work scope and costs can increase.
AFI-KLM E&M favors an on-condition approach to determining the work scope, for example in the work-scope planning guide for the fan hub frame.
Duration of shop visits varies according to work scope, scrap, part repair and exchange policy. Quick turns to fix specific defects usually take fewer than 60 days, while performance restoration takes at least 90 days. Forest says the supply of used serviceable materials is limited, especially for the -100 series, so salvage repairs and parts supply affect turnaround time. Executive services leader Judd Tressler says GE operates a used material business in Dallas and Amsterdam and has successfully incorporated used materials into engine repairs to meet demand and intended shop times.
Tressler emphasizes GE’s continuing investment in upgrading its engines. In 2017, a fuel-burn upgrade was released on GE90-115Bs that provides about 0.5% of the total 2% fuel-burn savings on Boeing 777-300ERs and 777-200LRs. The upgrade mainly includes a new high-pressure turbine active-clearance control manifold to provide tighter clearances at cruise, optimizing the turbine shroud grind to tighten the tip-to-shroud clearances, and a core compartment cooling valve with improved reliability. GE offers upgrade kits that can be installed during a routine shop visit.