Starter Motors

[Skytrucker87]

Anyone got an idea why the starter motors fitted to RR engines installed on B757 have such a high fail rate and when they fail the failure tends to be catastrophic. Any ideas?

[spannersatcx]

perhaps it's the operator?

[near enuf is good enuf]

Workin' 75's for 10 yrs and never heard of it!!!!
But then again I am Avionics.

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So that you may not be the martyred slaves of Time,
get drunk, get drunk,
and never pause for rest!
With wine, poetry, or vitrtue,
as you choose!"

[This message has been edited by near enuf is good enuf (edited 15 October 2000).]

[Blacksheep]

According to the info before me right now, world fleet unscheduled removal rate for Starter P/N 774984-1 is 0.05 per 1000 component hours flown over the last 12 months, 0.06 over last 3 months.

MTBUR = 20,000 hours or 8,900 cycles.

Make what you will of the numbers, but they don't look like too much of a problem to me.
Nevertheless, as my old school teachers used to say "Could do better"

**********************************
Through difficulties to the cinema

[HiSpeedTape]

Not had to replace one in the past five years. Weekly check / replenishment of oil level and mag plugs is all that is generally required in my experience.

[Lu Zuckerman]

To: Blacksheep

Dear Blacksheep or, should I say Baa Baa (joke).

Skytrucker87 was addressing what he felt was a high failure rate of the starter motors on the RR engines on a B757 and that is not the same as MTBUR. If your figures defined the MTBUR as 20,000 hours then the mean time between failure for that component is 23,529 hours. Another point to consider is that the calculated or predicted MTBF is a statistical mean for the fleet of B757s and not the failure rate for one starter motor. That means from a statistical point of view every 23,529 operating hours for starter motors in the fleet you would expect one starter motor to fail. However, since the starter motors are just used to start then you can use cycles instead of operating hours as for a generator which operates from block to block. If it were determined that one cycle was .1 of the block to block time then the MTBF would be one failure every 117,645 hours of aircraft operation since there are two starter motors per aircraft.

A calculated MTBUR is derived by multiplying the calculated or predicted MTBF by a constant which for this type of equipment is .85 or, 23,529x.85= 20,000 hours.

These figures are developed by the manufacturer of the unit under analysis.

The MTBUR figure you quoted was derived from the operational history of the starter motor. What you have to do is to calculate the differences between the predicted MTBF and the demonstrated MTBF. If the demonstrated MTBF is less than the predicted MTBF then you have a claim on the warranty
for the starter motor. I am not disputing what was mentioned in the posts above that referencec magnetic plugs and oil or, operator error. All of these things come into play as modes of failure and their resultant effects. That's why the manufacturer is required to perform a Failure Mode Effects Analysis (FMEA)

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The Cat

[jetfueldrinker]

Can anyone tell me what MTBUR and MTBF stand for please?

[Blacksheep]

MTBUR = Mean Time Before Unscheduled Removal and MTBF = Mean Time Before Failure. Statistical terms that have distinct and very precise definitions in reliability engineering.

Lu is very detailed in analysing the meaning of the terms, but I preferred not to confuse the issue by going into detailed statistical analysis. The MTBUR came from reliability data circulated among us Technical Services people. Put simply, the MTBUR hours and cycles figures given suggest that the B757/RB211-535E4 starters do not have a fleet reliablity problem.

spannersatcx said it more succinctly in four words. Skytrucker87's company may have an in-house problem.

**********************************
Through difficulties to the cinema

[This message has been edited by Blacksheep (edited 20 October 2000).]

[jetfueldrinker]

Thanks Blacksheep. I must admit that I have not come across too many unschedualed starter motor replacements in the 8 or so years that I have been playing, er..... I should say, working on 757's, but the starter oil does get changed on OOP, 'A' check and 'C' check intervals. Perhaps the problems that our friend has experienced may be due to the oil that is used in his companies aircraft. We had problems with, I think, ASTO 555, but after we put 560 in those problems, mainly found on IDG's, went away. But back in the days of good old 2380 there were no problems what so ever. The only reason for the change was financial as 2380 is about double the price of 555 and 560 is about 3/4 the price of 2380. It is a bit like putting cheap oil in your car really; it might be alright for a year or so, but if you want good service from your engine then you put good oil in it and have it changed regularly.

[Aogman]

Skytrucker's question was well backed up with failure rates - I can't remember the figures now but I know it's bl**dy expensive at $22000 US a throw. We have troubles on the same operator with FFGs and IDGs I like the oil theory although Woodward Governor and Sundstrand ( the respective OEMs) say there is no correlation.

Throwing in different unit what do people know about the BSCUs and trouble shooting? Our NFF rate is 50% (industry average is a very high 25) Messier put this down to poor fault finding. Does the BSCU have too much to do for a single unit? I'd be interested to hear in any comments these things cost my company a fortune.

[mriya225]

Okay kids, take it easy on me - I'm still a rookie: :)

I would initially suspect lube trouble; barring that I'd double check my alignment and torque values (this is assuming I've checked the manual to be sure I'm using the correct starter [parts ordered/delivered may not be correct])...

If I'm doing everything right there--then I probably need to back up and look for an electical problem with damaged wiring, poor connections, voltage regulation or a faulty generator. I would also check the clearances on my cranking shaft just to be sure there isn't a wear problem tearing up the component.

Starters shouldn't burn up with any noticeable regularity...this is just what I would do to find my culprit. Be kind if I'm wrong.



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Patience is letting your motor idle when you feel like stripping your gears.

[near enuf is good enuf]

mriya225,

I'm totally with your KISS (keep it simple simon) approach. 99% of defects will be sorted out through just checking the basics IAW the MM.
The only problem with your troubleshooting of the RB211-535 starter is that it is an air starter!!!!

------------------
So that you may not be the martyred slaves of Time,
get drunk, get drunk,
and never pause for rest!
With wine, poetry, or vitrtue,
as you choose!"

[SchmiteGoBust]

Iagree Mryia225,
Is the problem related to a particular installation?It may be worth checking the correct bleeds are open on the start cycle..could just be one jammed shut loading the compressor!!
Worth a guess anyway, stranger things happen at sea....


[This message has been edited by SchmiteGoBust (edited 21 October 2000).]

[mriya225]

Before I lose all credibility, let me explain...

The school I'm attending (C.A.T.) had ONE turbine left, until about five months ago. That class was doing their first inspection & run-up--like all of us are dying to do from the minute we agree to pay $20,000 for the priveledge--when there was a high pitched whirring followed by three very deep KA-BLUNG's.
They shut that old JT8D down but the fifteen foot cone of fire, jetting out the back, took a good seven to eight minutes to die down. I don't need to tell you all that that engine is wasted...
We still don't have a replacement (or even the hope of one in the near future).
I haven't gotten to turbines yet--not that it matters--it'll all be theory anyway. Hell, even our recip training has been primarily theory (many of them are missing parts, all are badly out of tolerance and none of them will actually fire up and run).
So essentially, I'll come out of school $20g's in debt, having never worked on an engine and seen it run afterwards; nothing more than theoretical knowledge in powerplant. Believe me when I tell you that it scares the hell out of me too!
Suffice it to say, that I do everything I can to pick up as much knowledge as I possibly can, from wherever I can. So, if at times, I come off as a little dense, please try to understandd that I'm really trying to keep up but I'm poorly equiped.
These forums are so helpful, and even though sometimes I look foolish, even that can be instructive. So, be patient with me while I stumble towards a better understanding and a greater degree of competence.

Cheers,
m.

[SchmiteGoBust]

With you all the way Mriya. We're all still learning all the time through personal experience or other peoples experiences. Anybody who thinks he knows it all is a danger!! Keep your learning head on-it will always stand you in good stead. Good input in any case!!

[jetfueldrinker]

To Mriya

We in this industry can and never will stop learning. The day we stop is the day we die, and this is because of the nature of the job that we take on. I have been in this industry since 1973, both military and civil, and there is no way that I can ever say that I know it all. And it would be a foolish person who reconed that he did. So keep at it, sue the ground school for having inadequate facilities and good luck for the futuer. BTW, when I was going through training someone burned out the turbine of a turboprop during ground runs. He pushed the throttle to it's open stop instead of just going up to max. torque. Ouch! But he learned from that.

[mriya225]

SchmiteGoBust & jetfueldrinker,
Thanks so much for the wise and encouraging words.