The GE 90 includes 26 life-limited rotating parts and three stator parts. The lowest limit is found on the HPT with a 3,500 flight cycle limit, while the highest is 30,000 cycles. One part in the HPT has a life of 3,500EFC, another 9,500EFC and others 15,000EFC. Other engine parts, such as the HPC, have lives of 9,800EFC, 10,000EFC and 11,000EFC. The list price for a full shipset of LLPs is $8.07m.
Life limits are defined by the engine’s operational thrust rating and operators must ensure the life used is properly tracked.
The average GE90-94B time on-wing for first run is 16,000-18,000FH. Considering the limiting LLP life is 3,500 cycles, engines operated at the lower ratio will have to be removed to replace this part, while long-range engines will not be affected and are removed for performance deterioration. Once removed, the motor will typically need a core performance restoration — i.e. high pressure compressor and combustion chamber modules will need refurbishing and the high pressure turbine will need overhauling in order to replace the limiting HPT interstage seal.
Once the engine has had a first shop visit, it should have enough performances to remain on-wing for 13,000-16,000FH when operating at a flight ratio of six. At the time of removal, an overhaul will be necessary. The total hours and cycles accumulated will be 29,000-34,000EFH and 4,000-5,700EFC; consequently the replacement of LLP will have to be carefully evaluated considering the expected on-wing time following the repair.
For some airlines, operating the engines at a ratio of two and with engines reaching an interval of 14,500EFH and 7,300EFC, a few LLPs will have to be replaced.
The interval post overhaul is usually equivalent to the first run (16,500 - 17,500EFH and 4,000 - 4,400EFC for operations at 4.0EFH per EFC and 18,500 - 20,000EFH and 2,300 - 2,500EFC for operations at 8.0EFH per EFC). It should be noted that GE has now introduced a new HPT seal with higher life limit; therefore the 3,500 limit will no longer be present.
The GE90-115B engine is still in the ‘young phase’ and removals have been few. This is mainly for technical issues and not for performance restoration, making available information limited. Since the engine is used in ultra-long flights, cycles are limited. The expected EGT margin of new engines is in the range of 40°C for the -115B and 60 Deg C for the -110B version. Based on the experience accumulated on the “smaller” engine model and on on-wing performances, the manufacturer and operators are expecting a first run of between 2,000 and 20,000 flight hours. Similar to the smaller version, a performance restoration will be necessary to restore serviceability and achieve a second run of 15,000-17,000FH, with the limiting factor being most probably the HPT interstage seal. An overhaul type of shop visit will allow the engine to be on-wing for a time similar to the first engine run.
SGI’s experience is a first shop visit costing in the region of $4m. The second shop visit will be both more extensive and more expensive, in the range of $5m. Shop visits are highly dependent upon engine thrust, utilisation, environment and engine standard. Considering the two shop visits costs and the intervals indicated, cost of the engine is between $252 and $310 per hour.
The average utilisation hours/cycles ratio is 5.4. China Southern and Saudia use the GE90-powered on medium-haul services at FC times of 2.5-4.0FH. Air France, Austrian, British Airways, Continental and KLM use the aircraft on long-haul services at FC times of 6.5-9.5FH.
Because of the newer and long range aircraft application, the 115B version has a much higher average ratio (7.1) and accumulated 3 million FH and half a million flight cycles. The 110B1 version with Air India is usually operated at a ratio of 11-13.
The above from a GE handout.
According to Gulfstream, by way of comparison, the GV, which is a long range business jet capable of 14 hour legs, has a ratio of 2.2 hours.
Since your favourite is the Citation, I checked the usage pattern of one model, among the many available, and CESCOM reports an average annual utilisation of 275 hours and the average trip length 435 miles. The Encore had a trip length of 393 miles.
Vast difference between airline and business jet.
It will be noted in the above that an airline engine may be removed for rectification, not because it has reached an hour or cycle limit, but because fuel burn has become excessive. Having to off load pax or freight in order to load extra fuel for a hungry engine at some point becomes self defeating economically.