Allison 250 Turbo-Shaft.

[Dennis Kenyon]

Hi Pruners ... I've been asked to produce a 'risk assessment' for an MD 500 operation which requires short periods of hovering at lowish altitude. (say circa 175 feet AGL) I've trawled the RR and Allison internet sites, but cannot come up with information providing historic shut down/failure rates for the Allison C-20/C-20B series engines.

Any whizz kids on here who can help? Thanks in advance lads. Dennis Kenyon.

[Aesir]

I like that you call it an Allison and not RR

I read somewhere (500guy): "Rolls Royce claims allison 250 series engines have a 1:10,000,000 flight hour Design/Manufactured parts (properly installed) failure rate".

http://www.pprune.org/rotorheads/479...ure-rates.html

[lima500d]

Hi Dennis

I have spent a bit of time doing low level stuff in the 500 and to be honest I couldn't think of a better tool for it. Mainly around power lines and fires if that is relevant. Talking to the more experienced 500 drivers and maintenance people they have all talked about when in the rare event the donk does go quiet it is probably one of the best machines to be in. I have been told on many occasion by the guys that work on them that the 250 - C20b is one of the most reliable turbines out there.

Hope this helps

Steve

[Saint Jack]

"...I like that you call it an Allison and not RR...." Heck, I can remember when it was Detroit Diesel Allison.

Seriously, I can't quote any figures but the failure/shut-down rate must be very low for a well-maintained engine - do regular compressor rinsing, regular engine washes (chemical washes) and keep the fuel nozzle clean. Perform regular power-assurance checks to ensure everything is good and it will give you many hours reliable operation.

[spencer17]

Have a couple of 1000 hours on the 500 and never had trouble with the Allison.
We did AG operation, spraying and spreading fertilizer. Really dirty jobs, but thanks to our engineering crew, no let down.
And for the 500: very rugged machine due to the centre frame between front and back seats. I'de rather crash in a 500 than in a 350

"Heck, I can remember when it was Detroit Diesel Allison." Me too sh.t must be age related.

[Shawn Coyle]

…and keep the P3 line B-nut torqued properly (and torque striped too).

[Bob Denny]

Slightly off-topic: History of the Allison-RR Model 250 Turboshaft (acrobat/PDF)

[Dennis Kenyon]

RR/Allison/Detroit ETC 250.

Thanks lads .. some intriguing experiences ... but I need a figure !!!! Cant' really believe the 1:10 million hours suggestion. Any more help please as my deadline is just three days away. The internet hasn't been any help. Thanks again Gents. Dennis K.

[Dennis Kenyon]

250 engine

Oh ... and I just thought I'd add ... my client's idea is to hold a 175 feet AGL display hover around 100 feet from paying spectators. Type will be a 369D or C model. Should provoke some discussion if not produce an actual failure failure figure!

Dennis K again.

[snotcicles]

I've asked Rolls Royce in the past for this kind of information on the 250-C20 series and they don't release it to the public. It is a very reliable engine but for some sort of corporate privacy reason, the statistics appear to be off limits. Bell has some data from several years ago on the 206 which is about as much as I could ever come up with.