Turbine Engine Failure Rates?

[Friendly Black Dog]

Can anyone point me in the right direction to find some stat's regarding the "failure" rates of turbine engines installed in helicopters. Ideally I would be able to disregard running out of fuel as a "failure" cause.:ugh:

Cheers

[riff_raff]

FBD,

You can get some great technical reports on military rotorcraft here at this website (http://www.dtic.mil/dtic/). Just search the technical report database using criteria like "rotorcraft failure modes".

riff_raff

[Shawn Coyle]

One of the major problems with data is that in the USA, helicopters operating under Part 91 that have an engine failure and are able to land with either no damage, or damage within prescribed limits, don't have to report the failure to the NTSB.
This skews the data enormously. And no-one seems to know of a solution!

[catseye]

Ogsplash may be able to assist. I had some very long discussions with him in relation to Single engine vs multi engine safety relating to engine failure other than running out of fuel. He has some recent hands on incident investigation experience at least for Oz trends.

now retreating back to High Wollemi.....

[Friendly Black Dog]

Hey Cat,
Would Ogsplash be on tour in the highlands at the moment? If so I'll email direct.
Cheers

[HeliTester]

Certain European twin engine Commercial Air Transport helicopter operations require engine failure rates no worse than one per 100,000 hours. Many different models have successfully demonstrated that capability, but I’m not aware that the statistical data are available within the public domain.

[Savoia]

Is there any substance to the claim that Turbomeca's Astazou (first run in 1957) has the most reliable service record of any turbine in rotary wing history?

Is there a turbine which has been identified as achieving this accolade?

[Shawn Coyle]

Savoia:
I don't have any hard data, but I can tell you something from an accident that I worked on in Romania in the early 90's that involved an Alouette III. Turbomeca told the Romanian authorities that aside from someone not servicing the engine properly with oil, or running out of fuel that they had had no more than two engine failures reported on the Astazou model.
The UK CAA at one point about the same era had stats that showed the failure rate of Turbomeca engines was 1/20th of another popular model, and I'm sure the numbers in favor of Turbomeca were heavily skewed because of the Astazou (there being few other engines of their manufacture at the time).
But no hard numbers that I'm aware of.
And some of the reliability had to be at the price of fuel consumption - the Astazou was about 25% more thirsty than the competition for the same horsepower as I recall.

[fly911]

I was wondering the same thing when I started flying turbines in 1980. As close as I could get was that Allison claimed that the rate of "early removal" on their 250 series engines was one in 50,000 flight hours. While it doesn't answer the question directly, it says something about reliability.
There are many reasons for an engine failure, from a loose fitting on a fuel control to sloppy refueling practices. The best defense against engine failure is a good preflight inspection. A wise instructor of mine once told me that a helicopter will almost always warn you before it lets you down. (Ok, he didn't say 'Almost', but I had to throw that in for credability). It's up to you whether to heed or ignore the warning signs.

[catseye]

FBD, I think he is about mid tour at the moment. :cool:

Probably should say that trying to run engines on vapour is a common thread.

[500guy]

http://flightsafety.org/fsd/fsd_aug91.pdf

Here is a great report with all that info, but its old.
Rolls Royce claims allison 250 series engines have a 1:10,000,000 flight hour Design/Manufactured parts (properly installed) failure rate.

[Friendly Black Dog]

Thanks Cats'

He audited the hell out of me a couple of weeks ago! I well and truly have his email.

Cheers

[S3R]

Hi all,

Does anyone know of any new data on this? Specifically, the failure rate per 100K flight hours for a gas turbine - in a helo.

Thanks.

3R.

[md 600 driver]

Savoia:
I don't have any hard data, but I can tell you something from an accident that I worked on in Romania in the early 90's that involved an Alouette III. Turbomeca told the Romanian authorities that aside from someone not servicing the engine properly with oil, or running out of fuel that they had had no more than two engine failures reported on the Astazou model.
The UK CAA at one point about the same era had stats that showed the failure rate of Turbomeca engines was 1/20th of another popular model, and I'm sure the numbers in favor of Turbomeca were heavily skewed because of the Astazou (there being few other engines of their manufacture at the time).
But no hard numbers that I'm aware of.
And some of the reliability had to be at the price of fuel consumption - the Astazou was about 25% more thirsty than the competition for the same horsepower as I recall.

shaun didn’t the Romanian Alouette’s have an artouste engine. I know there is a variant of the Alouette 111 (319) that has a astazou engine but I don’t believe the Romanians had them I imported 6 ex Romanian alou 111 (316) and they were all artouste

steve

[JimL]

S3R,

Data is collected by all the engine OEMs and sent to the airframe manufacturers; it is then combined with airframe failures (those that are not directly related to the core engine). The aggregated data is then distributed, as information, to (some) operators and as a more detailed analysis to the State's CAA.

In general, most engine/airframe combinations will meet a reliability rate of 1:100,000 hours. In recent years some manufacturers have achieved better than 1:1,000,000 hours for some of their types. On the other hand, some manufacturers have experienced issues and have not maintained their 1:100,000 reliability rate.

The 1:100,000 is the (engine/airframe) reliability rate that is used by some States to qualify their operators for the use of 'exposure' (where a failure would result in a hazardous or catastrophic event). When this target rate is not achieved, the manufacturers make a great effort to establish the cause and rectify it. To smooth the rate, a moving window of 5 years (data) is used - this removes problems due to skewing (because there are so few failures). However, as has been seen recently, failures tend to bunch; this calls for expeditious action as soon as a trend is noted.

The system used by a number of States (soon to be adopted by ICAO) allows failures to be washed out of the data when faults are established and rectification put into place.

In answer to your question: there does not appear to be a centralised system of data aggregation; however, it can be assumed that the 1:100,000 reliability is achieved unless information is present to the contrary. It should not be assumed that a turbine installed on one helicopter type achieves the same reliability as one installed on another; experience has shown that failures due to the installation are more prevalent.

Jim

[megan]

Jim, does an engine pulled before reaching its overhaul time count in the statistics? It's a long time ago but seem to remember we were pulling engines on the 76A after about 400 hours, at overhaul they were blueprinted. We operated them hard, always max EGT on take off with about five to seven landings per hour. Only ever had one engine blow up in flight over a period of some eighteen years in a fleet of six.

[JimL]

Ensuring that engines achieve their predicted reliability is governed by several factors - e.g. continuing airworthiness using condition monitoring and power assurance. This sometimes results in engines being replaced before their scheduled in-service life time. Here is a copy of some guidance on engine reliability / monitoring:

Engine Reliability / Monitoring

The reason for monitoring engine reliability is to eliminate ‘abuse’ or to spot a ‘trend’ that will eventually lead to failure if no action is taken; this is particularly important when the helicopter is used in a dual role – i.e. aerial work as well as commercial air transport. A reduction in power revealed through a scheduled ‘power assurance’ check is a useful indicator, providing it is used in accordance with manufacturers procedures for rectification or removal. No over-temp or over-torque is likely to result in immediately failure, but they can be precursors to eventual failure.

It is unlikely that any current system (apart from chip warning) will provide an ‘immediate’ warning of impending failure; in any case, if operating in PC3 over a hostile environment an indication of failure could not be acted upon without consequence.

An operational approval system should require the engine/type to be assessed for reliability – and specify a means for achieving that. This requires the reliability analysis and reports, produced by manufacturers, to be available to States on request. The measure of reliability is a principal element (power unit failure rate per 100,000 engine hours). Generally, for turbine engines, reliability for the helicopter/engine combination is established by major manufacturers.

Flagging exceedances, eliminating abuse and spotting trends, is a way of ensuring that the ‘reliable’ engine/type, used for operations with exposure, stays within its reliability target. Monitoring systems may be used to encourage pilots not to abuse engines, and operators to control trends and report failure. Thus, instilling a culture of caring for propulsion units.

With modern control of engines using Full Authority Digital Engine Control (FADEC), and other systems, there is often built-in control and potential for monitoring. Abuse of engines is prevented by FADEC or shown as an ‘indelible’ flag that must be recorded and investigated.

Only with legacy helicopters should it be necessary to ‘bolt-on’ an engine usage monitoring system. Such systems are now relatively low cost and can pay for themselves just by eliminating hot starts.

Statistically, most engines can be shown to be within the 1 x 10-5 to 1 x 10-6 reliability range. Abuse control is aimed at ensuring they stay within that range. Further improvement in engine reliability by monitoring is unlikely to change the risk profile to any discernible degree.

In assessing how much weight to give to engine monitoring systems in the risk assessment, it is necessary to be realistic about the effect of reliability on the risk profile of the exposed operation. It is likely to be less than one order of magnitude. Potential gain may have already been realised by manufacturers installing the latest engine control and monitoring equipment as standard.

Considering the statistical reliability of engines is one way to assess risk. Not all aircraft engines have the same reliability and it is reasonable to require a higher level of dependability for particular ‘types of operations’ or flight over specific ‘geographical areas’. Certain aircraft/engine types might, appropriately, be deemed unacceptable for some high-risk operations.

Assessment of reliability is a complex task because it relies upon the reporting of failure, regardless of outcome, and an accepted method of collecting and collating flying hours for the helicopter/engine type. Without these, it is extremely difficult to establish failure rates on which any measure of reliability can be based but neither failure nor flying hours are required to be reported under the existing regulations of some ICAO Member States.

A comprehensive usage monitoring system, as well as the provision of failure and usage reports to the manufacturer, can provide data for trend monitoring and local analysis of health as well as reports of exceedances. These are likely to have a beneficial effect on local culture and reliability statistics as well as providing evidence of the precursors of failure.

Maintenance

It is essential that when operating with exposure, the maintenance programme includes the helicopter/engine modification standard using the preventive maintenance actions recommended by the helicopter and/or engine manufacturer. This representative guidance has been useful in establishing the categorisation of failure – with respect to exposure – and providing a method of establishing and promulgating reliability rates.

Maintenance is often overlooked as a risk mitigation strategy since it is considered a normal aspect of any air operation. If a quality maintenance program is in place, an additional preventative maintenance and trend monitoring regime can be considered as risk mitigation for operations with exposure. This must be part of a controlled system to avoid Human Factors events in unnecessary intervention procedures.

The modification standard that is applied to any helicopter/engine combination is dependent upon the assessment by the State of the susceptibility to known failure(s) of a component, and the subsequent risk to operations. For example, where a component is an element of a redundant system, rectification might be contained in a ‘bulletin’ rather than a ‘directive’, or time to rectification might be less stringent.

In cases where redundancy provides no protection: for PC2, exposure in the take-off and landing phases; or, for PC3, exposure in any phase, the State should ensure that operators are made aware of, and apply, the most stringent of modification standards with respect to any known susceptibilities.

In addition, the State should ensure that a system of preventative maintenance and trend monitoring is used to spot precursors ahead of failure as an element of the maintenance system and the overall operator Safety Management System.