Tackling LEAP issues

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Oman Air’s Boeing 737 MAX A40-MA powered by CFM56 engines.

IN PART because CFM is used to manufacturing and delivering very large numbers of engines annually (CFM56 deliveries in 2017 totalled 1,444 and LEAP deliveries totalled 459), its production ramp-up for the LEAP engine is even larger-scale than Pratt & Whitney’s ramp-up for the PW1000G. CFM expects to nearly triple to about 1,200 engines the LEAP production rate this year and is planning to be able to deliver 2,000 to 2,200 LEAPs annually by 2020. By then CFM56 production will have fallen to a long-term residual rate, CFM only manufacturing new CFM56s as spare engines and as powerplants for the 737-800-based Boeing P-8A Poseidon maritime surveillance aircraft programme.

Like Pratt & Whitney with the PW1000G, CFM ran into production and in-service technical issues with the LEAP programme in 2017. LEAP production last year ramped up a little more slowly than CFM had planned, creating a delay of four to five weeks for any given engine, but the manufacturer expects to complete rectifying the productionrate issue this year. Meanwhile, CFM has completed retrofitting installed LEAP engines starter air valves which needed replacing. The company has inspected and reinstalled more than half of the 70 turbine rotors which needed to be removed from installed LEAP-1As because of a potential productionquality issue.

Another technical issue has also affected initial LEAP engines in service: peeling of the waterresistant coating applied to the high-pressure turbine stage 1 shroud, the first component in any commercial-aircraft engine made from ceramic matrix composite material. This issue has caused exhaust-gas temperature (EGT) margin degradation in some engines, affecting their performance levels. However, CFM says both the LEAP-1A and the LEAP-1B have additional EGT margin capability over that normally provided by the engine-control software. The company is also making that capability available in affected engines by updating the software.

CFM is also addressing the core CMC-coating peeling issue by developing a more robust coating for the stage 1 turbine shroud.

However, one potentially disruptive LEAP issue in LEAP- 1B engines may still have to be addressed. According to UK aviation consultancy IBA Group, the extensive early deployment of Boeing 737 MAX 8s on longhaul routes by low-cost carriers Norwegian, flydubai and Lion Air has required their engines to be operated at very high levels of take-off thrust far more often than CFM expected. The engines of these aircraft are achieving only about 2,000 hours on wing before needing to be removed for overhaul, where they should be achieving up to 30,000 hours on wing. Whether this issue is related to the premature EGT margin deterioration caused by peeling CMC coating is not yet clear.