View Full Version : Robinson R44 Sprag Clutch Failures

What Limits
24th Sep 2008, 18:42
We are beginning to see far too many of these at the moment. Anyone else experiencing failures/slipping/banging? Or has anyone else inspected one early and found excessive wear or damage?

24th Sep 2008, 18:53
Have these just been found at inspection or reported by pilots? :confused:

What Limits
24th Sep 2008, 21:22
We have had pilot reports and have discovered these problems during overhaul. Some clutches haven't even made it to mid-life before having to be replaced. Just wondering if its us or if others are having similar problems.

25th Sep 2008, 09:54
The following may be of intrest.

would be interested to hear of issues with r44 sprag clutches. The NZ CAA has issued an AD requiring them to be inspected every 500hrs. As far as I can find out almost every clutch inspected has required either complete replacement or replacement of parts i.e. bearings or the sprag unit.

I think NZ is the only country requiring this inspection ( Robinson only require that an engineer listen for noise with a stethascope - mine had no noise but still required a replacement sprag unit ) which raise the possibility of lots of R44's flying in other parts of the world with clutches that would be unserviceable here.

Robinson had a court battle with Dana, clutch manufacturers, a few years ago re defective units . This resulted in a $M+ settlement but these are not the units now giving trouble here.

Comments ?


Re: R44 Sprag clutch
« Reply #2 on: 04/19/08 - 21:21 » Quote Modify Remove

Hi Grant,

As far as I know there have been no in flight failures. Things started when some clutches that were making "strange noises" virtually fell apart when disassembled. In my case the clutch was " one of the better ones " at 500hrs but had wear on the sprag teeth and the maintenance folk weren't ( I think ) prepared to re assemble it with their name on it !

It has occurred to me that given how these things operate maybe some wear on the sprags is normal and maybe we are just being over cautious. On the other hand pulling in power and discovering that the engine is no longer connected to the rotors would be a bit of a nuisance so I wasn't prepared to argue.

I guess the point is that if this is a the scenario every 500 hours it will add a lot to operating costs and in other countries, if our CAA are right, could be an accident waiting to happen.

FurDefect, Occurrence # 07/1614
Part: Spag and Clutch shaft Part Manufacturer: Robinson Helicopter Company
Aircraft Model: Robinson R44 II ATA Chapter: 6300
Part Model: Raven 2 Part Number: C-188-3
Date: 09 May 07 Date Released: 04 Apr 08
TSI Cycles: TSI Hours:
TSO Cycles: TSO Hours:
TTIS Cycles: TTIS Hours: 900

After numerous reports of premature clutch failures, the operator requested a special inspection. Clutch sprag was found to have 3 broken pawl segments. A total of 14 other premature failures are also noted on the CAA database for the R44 helicopter. Airworthiness Directive DCA/R44/23 has been published, reducing inspection intervals from 2200 hours to 500 hours.

Main Sources of Information: Industry Reports


ther .....

RJ Kanary
25th Sep 2008, 13:49
Is this one way clutch perchance the Epilogics® Mechanical Diode? It seems like it is.

It's been used in some automotive and light truck transmission applications with what is best described as limited success.

Some applications that require operating in the free wheeling or over run mode for extended periods of time have demonstrated catastrophic failures in an unacceptably short time.{In spite of the patent holder's allegation that the locking plates 'fly' on a cushion of oil, preventing metal to metal contact. }