The 777 has long been established in its market of medium- and long-haul routes, as the world's largest twin engine commercial aircraft. The 777 entered service in 1995 via the 777-200, and now comprises five passenger series: the 777-200, -200ER, -200LR, -300, and -300ER. There is also a freighter version, the 777-200F. The 777 seats 310-390 passengers, depending on the series, and class configuration and layout of passenger accommodations (LOPA).
There are two main engine options available for the 777 variants: the General Electric (GE) GE90; and the Rolls-Royce (RR) Trent 800 engine families. The PW4000-112 can also equip both the -200 and -300. 473 passenger configured 777-200 series aircraft remain in service, in addition to 747 passenger configured 777-300 and -300ER aircraft.
The A380 now competes in some of the same markets as the 777, sharing many destinations on several operators' route networks. Emirates, for example, operates a fleet comprised solely of 777s and A380s. British Airways (BA) operates the -300ER and the A380 to Singapore and Hong Kong. The A380-800 is powered by the Engine Alliance GP7200 and RR Trent 900 series. To date, there are 125 passenger-configured A380s powered by the GP7200, and 83 equipped with the Trent 900. Although Airbus has suggested the A380-800 could carry up to 544 passengers in a three class LOPA, operators typically have 490 seats on long-haul routes.
While the 777-200 and -300 legacy fleets are in decline, the A380 is growing. According to Flight Global Fleet Analyzer, 106 passenger-configured A380s are on order with Airbus, of which 70 are Trent 900-powered.
The GE90, GP7200, Trent 800 and Trent 900 families will therefore be examined. Each engine has previously been summarised by Aircraft Commerce (See Big engine in-service performance & maintenance, August/September 2008, page 41, Operators and Owner's guide: GE90 Family, Issue 84 Oct/Nov 2012; Global engine shop activity, Issue 64 Jun/Jul 2009; Operators and Owner's guide: Rolls-Royce Trent family, August/September 2012, page 3). This examination aims to show approximate removal intervals, shop visit (SV) costs and the performance capabilities of each engine. Where applicable there will be insight into key removal drivers, modification work, and service bulletins (SBs) or airworthiness directives (ADs) that might impact SV workscopes. Such factors may also force early removals and therefore affect removal intervals, or the overall mean time between removals (MTBR) if an issue is found to be fleetwide. Life limited part (LLP) demands will also be provided.
Naturally, not all engine maintenance is routine. Newly certified engines may undergo hospital visits to inspect and restore core modules if performance loss is monitored or an irregularity observed. Unscheduled SVs can also occur. These fall outside the scope and definition of a scheduled SV; the SV pattern typically alternating between a hot section or performance restoration, and engine overhaul. LLPs will usually be exchanged during an overhaul. Hospital visits are usually quick-turn and require a limited workscope, with modular inspections and limited repair or component replacement, rather than full core disassembly. Fuel nozzles may have to be changed, for example, or blend repairs carried out due to borescope inspection. Overall, the workscope is light, although the hospital SV may affect and interrupt the subsequent removal to the next planned SV.
Engine performance for each engine is determined by the following parameters: specific fuel consumption, engine flat rating temperature; exhaust gas temperature margin (EGTm) or turbine gas temperature margin (TGTm); average engine flight hour (EFH) to engine flight cycle (EFC) ratio; take-off de-rate; and ambient operating temperature in addition to overall removal intervals. Engine performance allows operators to establish exactly how the engine is working for their fleet efficiency, in terms of how many EFH and EFC the engines are accumulating on-wing before they require removal and extensive maintenance in the form of a performance restoration or overhaul.
"EGTm loss is typically monitored against EFC, since it is a more accurate parameter than EFH," explains Graeme Crickett, senior vice president and head of technical at Sumisho Aero Engine Lease. Crickett explains that other factors, such as high pressure turbine (HPT) module performance, will influence EGTM, as is currently the case with the GE90-110/-115 series.
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Pre-Covid, IBA forecast strong growth across the entire aftermarket: narrowbodies, widebodies and regional aircraft. There was an expanding fleet, heightened utilisation and increased demand for shop visits. The situation has evidently altered enormously and the most vulnerable assets, mature widebodies, will be the first to be withdrawn from shop visits.
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