I don't think you know them well enough to quote them then dis them.

It does beg the question.....and remembering the two crashes were not Bristow machines. Were they doing something the other operators were not?

Perhaps you are not familiar with the history of discussions about the various merits of the 225 and 92 that went on here for years.

Thus, you might not t have the background to make the comment you just did.

No, you have no evidence that reducing torque would have made any difference and one thing was certain, reducing cruise torque resulted in increased vibration. Not only obvious vibration from the rotor head, but vibration in the tail pylon are too. Vibration being a fairly destructive thing.


This idea was often mooted by folk with no technical knowledge but every time, EC (as they were then) said it was a bad idea.


Mind you, even at reduced cruise power it was still a lot smoother than an S92!

The 225 was the greatest thing since sliced bread according to virtually all the pilots (we did have one weird one who preferred the S92). Right up to the point, after 100s of thousands of hours, where one had a rotor head fall off. Yes that is a pretty serious achilles heel which unfortunately ruined the type, but in every other respect it was fantastic.


Bristow engineering did what they had to do and more. I don't know what the culture at the other operators was but from where we stood, it did sometimes seem as though they only did what the had to do. HUMS downloads being an obvious example.

HC,

Reducing Cruise Torque did alleviate the problem in the gearbox though did it not?

That is what I was told seemed to make the major difference in the frequency of MGB replacements....or was I told wrong?

During acquisition of the 225....did the issue of increased loading of the MGB become a topic of discussion?

Not really interested in that fanboy fight. But I know BHL well enough to pick out your BS.

Please feel free! We would all like to hear what you have to say.

If you are referring to the early days of the AS332 on the North Sea, there were excess wear issues with the gearbox when operating it at “fast cruise” pitch setting of 16° pitch which Bristow did for some time in order for the Bristow “Tiger” not to be outpaced by the Bell 214ST which was being operated by British Caledonian Helicopters (BCal). Bristow had a very high rate of in-service gearbox rejections during this period but I must emphasise that normal maintenance routines did not allow this to become a safety issue, it was purely a financial and maintenance burden. At or about the time Bristow bought BCal, Bristow reduced their normal cruise setting to 15.5° in line with the other operators.

North Scottish/Bond Helicopters always flew the AS332 at 15.5° pitch which was the recommended normal cruise pitch setting and never had any issue with gearbox rejection rates. It also made for a much more comfortable ride.

There is no point comparing the AS332 historical experience with that of the EC225 as it is a different gearbox. The EC225 is always best cruised at just below max continuous power. It keeps the vibration level down and there is absolutely no evidence that normal cruise power settings (used by all operators) cause any reliability issues.

BHL used 16.5 degrees pitch when 332 operations started then reduced to 16 degrees

16.5° could only be used below a certain mass, the exact value I cannot remember but it equated to about 3/4hr of flying if take-off was at MAUM. Vibration level was not good at max pitch and specific fuel consumption worked against you unless flying into a strong headwind.

15.5° was the recommended cruise pitch by AS which is what BHL reduced to after management came to their senses.

Recommendations maybe but in BHL marketed the 332L at 145 KTAS. Take off from ABZ in April 1982 was at 18410 lbs Planned fuel burn 1140lbs and planned TAS 145 at 16.5 degrees from TOC.

So what's exactly your point?
(Apart from showing again that you are a dyed in the wool Sikorsky admirer?)

Any new findings?
Any sign that the early Gearbox changes of the original 4 - blade Puma family had any failure path similarities with the problem in the 225?
Wear and internal cracking are totally different beasts. The 225 didn't (literally) lose its head due to simple wear.
Reducing torque wouldn't have necessarily prevented the cracking. The level of vibration isn't a linear function of torque. It is a complex function of multiple variables and there will often be vibration spikes at lower torque levels.

In the case of the 332L, yes definitely. But that was a different beast. It was rough as old boots at 16.5 CP. But presumably the reduction in CP was as much about sustained gearbox torque as it was about reduction in airframe vibration. I don't know.


In the case of the 225 it was much smoother at MCP than it was at reduced power. Also it was designed to be flown coupled in 4 axis but once you decided to reduce power, that was a bad idea (lots of collective adjustments being automatically made to hold a set speed). Or of course you could fly it in 3 axis but that had its own safety implications (look at the Sumburgh L2 accident) and the 225 had a big variation in torque with turbulence and roll. Although in both modes (3 and 4 axis) the 225 "protected" against overtorque by lowering the lever, in 3 axis this only happened after MCP was exceeded, in 4 axis it maintained torque a % or two below MCP.


And one has to be careful not to create new problems with a knee jerk change of policy. So if we had reduced cruise power, and lived with the increased aiframe vibration and slight safety reduction, who knows what damage that might have accumulated over 100s of 1000s of hours. Maybe the gearbox would have lasted longer but maybe something else would have failed sooner. Bear in mind this gearbox issue only manifested itself once in the hundreds of thousands of hours - albeit in a pretty catastrophic way. What other failures could increased airframe vibration due to cruising slower have created in those 100s of thousands of hours?


On your point about topics of discussion, yes having gone from the L to the L2, I felt that the L2 might have been a step too far in terms of the engines and transmission. And then along came the 225 with MUCH more power, same phyisical size engines, MUCH higher MTOM, a cruise power similar to both engines a OEI max contingency power on an L. Impossible!


But the reality was that it seemed less stressed than an L2, and in the context of Bristow did 100,000 hrs or so without major issue. Once people flew it, their doubts vanished.