Originally Posted by
SASless
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?
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.