Well, here's one example.

The stress in a highly heated part of the rotated machinery in a gas turbine is highly dependent on the temperature of operation, especially the peak temperature. Such that a change in operating temperature of only a few tens of degrees can commonly double or half the effective fatigue life of the component.

the parts are not manufactured to different standards; they are USED to different standards.

Military fast jets are not manufactured to lower standards than civil airliners. yet hardly any military aircraft manufactured in the 70s is fit for continued operation without substantial rework - think of all the rewinging programmes the military routinely conducts to extend the service life of older aircraft. When was the last time you heard of a civil aircraft being re-winged? They dont need to it, because they are "babied" compared to their military brethren - one aircraft flies at a sedate 0.8'g' to 1.5'g', the other between -1'g' and +6'g' perhaps.

It's all dollars and cents.

To design to an airline-standard cycle life (more specifically, Low Cycle Fatigue or LCF) a part will likely be heavier, use higher grade materials, have a more expensive manufacturing process, and/or more stringent inspection. This all adds to the cost.

Applying all these goodies on a bizjet engine that only flies 500 hours/year and which may become obsolete before it wears out, becomes a pointless exercise; and might drive the engine cost to uncompetitive levels.

In short, it can be done, but what's the point?

Blank Check, SSG, Kanetoads, whatevernext

I suggest you download the following presentation and educate yourself before your next posting on this subject.

SmartCockpit - Airline training guides, Aviation, Operations, Safety

In fact, there are quite a number of presentations on the smartcockpit website that would be beneficial to you :):)

Mutt

Mad - The only differentiation in 'USE' between airlines and GA jets would be reduced thrust departures and possibly a more vigorous inspection program.

So I'll give it to you that an airline submits an operating - maintenance program that helps the engine manufacturer feel more comfortable about allowing longer cycle limits. I am just curious what information the engine guys are crunching.

It's not hard to figure out that an airliner can push the engines out as far as the mechanic with a boroscope will allow based on visible evidence of damage, etc.

At issue are components like bearings, that can't be inspected, that are just allowed to run out say 4-5 times farther on an airliner, based on what?

I see it like this. Obviously the manufacturer doesn't want broken parts bringing down planes, but at the same time the airlines won't accept 3500 engine overhauls due to the obvious cost. I surmise that the engine manufacturers are being really conservative with corporate jets. (Greed)

So what's fair is fair, if the airlines can run their engines out until the mechanics see a problem, corporate should to. In fact I might talk to my local FSDO about this.

Our airline uses reduced thrust whenever possible. The program reduces the available takeoff distance by 1,000 feet to add some fudge factor when factoring the numbers.

Nice touch of conservatism, and I won't argue with it, as long as it produces the average fleet % reduction per the OEM's warranty.

But there's conservatism already built into the assumed temperature (flex) method, in that engine thrust is set per the flex temp, but the airplane wing is flying in the real OAT. So performance is better than book @ the real hot day condition.

BlankChecks,
Have you stopped to wonder why you are a lone voice on this subject? There are many tens if not hundreds of thousands of flying hours experience on the thread let alone site, who from experience know the theory to work in practice. Supported by evidence from the manufacturers and a big thumbs up from the shareholders and the passengers who fly in ever increasing numbers. Failure rates continue to fall as do operating costs, so please please tell me why you can't see the benefits?

SSG in all your various guises,

You do know that a number, increasing at that, of corporate engines are "on condition" including the CF-34 (CL-600 series), HT 7000 (CL 300), BR 710 (GLEX, GLF) to name a few. The HT 7000 is hugely derated. The BR 710 offers flex power take-offs thru the FMS.

Please stop extrapolating from one data point--the aging JT-15D. You are making the pros flying newer business planes look like an uneducated group of Neanderthals. Just saying'

GF

Off topic a bit
 

SSG et al. brings up an interesting point, namely bearings. He seems to be aware of a bearing life issue that's outside my limited (45 years) experience.

Bearings and lube systems on our engines have generally been very reliable; I can only recall one bearing on one engine type that required special attention, and it is no longer a worry item after the type achieved maturity.

Who else finds bearing life or reliability a significant worry?

My apologies. John banned me, and it took 5 minutes to get back on.
 

Another first time by SSG Version 11!, will we see another?

First, it is "you're", not your. It is a contraction, not the possessive.

Second, I am proud to be associated with Pprune members, such as mutt, Brian and FEHoppy. Can we add Old Smokey, if so, I am humbled?

Third, which way does the rotor thingy go?

Fourth, barit1, the only bearing failure I have heard of, as a design failure was of a military jet. A friend, tech rep and bearing engineer at the manufacturer and ANG pilot, was handed a handful of obviously broken parts, reported to be a main bearing. Asked what the original bearing looked like and a set of drawings, was told that he didn't have a clearance to see them. "Then, he replied, it broke.". j58, btw.

GF

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.