I think there are only 5 225s on the N register?

Five is also what the Flightglobal article indicated.
I think the SASless note above is entirely on the money. The 225 is incidental at best in terms of jurisdictional interest for the FAA, so they have no reason to try to second guess the EU authorities, but can let the courts resolve the issue.

They can return them to service but I know most of the UK offshore workforce are committed to not flying in them again. Pressure is being applied to the UK operators to follow Statoils lead. Confidence has been lost completely and the rush by AH to get them flying again before the accident investigation is completed is doing even more damage to the reputation.

The gear that failed
 

The gear that has been identified as the one that probably failed looks small. Working back from the rotor RPM and the related gear ratios can any tell me how many rotations these gears do in a life time?

Just to keep the thread alive and generate further posts I’d say impossible to tell, depends on usage.

From information previously posted on the crash thread, the Service Life Limit used to be 5000FH and the TBO 2000FH but the TBO is said to have been reduced to 1500FH. With a rotor speed taken as 265 rpm and the 2nd stage sun gear rotating at 820 rpm, I reckon the 51 tooth planet gear should ‘rotate’ at approximately 1013 rpm (about its own centre). To achieve the original 5000FH SLL a planet gear would have to rotate approximately 304 million times.

To answer the question asked though, in a ‘lifetime’ the planet gear may rotate anything between 607,800 and 304,000,000 times. That 'lifetime' would be based upon the directive to manually inspect all EC225 MGB magnetic chip detectors every 10 flying hours applicable, it would seem, to even brand new gears. It should be noted for fatigue considerations that cyclic bending stresses occur twice per rev of the planet gear.

SLL does not take into consideration ground runs or start up and taxi times etc. so these revolutions should be regarded as min figures/flight time only and assuming a constant Nr of 100% that the EC225 does not have.

I would say that SLL is a simplistic concept in that it measures time only. Fatigue crack propagation is also a function of load level with each cycle. I would hope that SLL is set with very conservative assumptions on the spectrum of load levels. Otherwise you would need to consider not only Nr but simultaneous Torque during all running. Even then, fatigue damage done in early life can be more significant than later. This was the case IIRC with tests on the bevel gear shafts.

You make a very valid point. From the outset this was one accident too many. Confidence was already very low when it happened. So the problem is not that the H225 is inherently an unsafe aircraft (I can't answer that), it is that a very high percentage of its passengers are absolutely convinced it is. The problem in an already declining NS is that why would an E&P company persist with this aircraft when current market conditions mean they don't have to. To most E&P corporate types another fatal accident involving a Puma gearbox is quite simply unthinkable! You need to get the culture here this isn't just about aviation.

The Chinook, a helicopter that has had decades of trustworthy service and is still is was effectively wiped off the North Sea and the international O&G patch because of a fatal accident as a result of a gearbox failure.

They solved the problem by stepping back a little. Perhaps Airbus could step back to modifying the 330/332 gearbox arrangement.

How many 234 Chinooks were there? Six. Not quite the same. And what happened to British Airways Helicopters in the North Sea is probably as relevant as what happened to the Chinook.

What if there had been accidents as a results of transmission failure in the workhorse type of the time?


S-61: NM in 1970, QA in 1973 (4 fatal), HN in 1977 (rotorhead), SZ in 1977 (rotorhead)(12 fatal), QS in 1978 (18 fatal), NL in 1983 and ID in 1988.

There would have been more. Bristow was prepared to 'buy the bullet' as far as the purchase was confirmed. The hold up was as to whether their customer companies would reinforce their decks. Mine, and other, names were down for the first conversions. The crownwheel gear disassembly put paid to that and so the Tiger (AS332L) was born.

They could engineer the snot out of the gearbox.

What people have problems with is there attitude to safety.

This can never happen again………..oh dear it has………..(Bevel shaft)

This is the only possible cause of the accident……..oh dear apparently it isn’t.

Not confidence building.

Good point about the planet gear teeth being subject to a full reverse bending load cycle twice per rotation. The EC225 MGB epicyclic output stage has a fixed ring gear, sun gear input, and planet carrier output. The planet carrier is coupled to the main rotor mast, so the number of planet gear tooth bending load cycles per rotor rev would be the no. of ring gear teeth divided by the no. of planet gear teeth multiplied by two. However, I would point out that the gears used in helicopter MRGB's are typically designed for unlimited fatigue life in tooth bending. Since root fracture of a gear tooth due to bending fatigue is a failure mode you never want to occur.

Your later comment about how the magnitude of load cycles and when they occur during the component's lifespan can have different effects on fatigue life is also relevant. Here is a good explanation of the Goodman relation.

Fasreastdriver

There were 10 BV234s, not six. As well as the six BAH bought, Helicopter Service bought four.

I take it this means bent in one direction at the sun followed by bent in the other at the ring once per rev?

A moment worth remembering.

The 234 continues to be the Star in Forestry and heavy lifting for Columbia Helicopters and are being joined by Surplus US Army CH-47's!

Anyone care to argue that Offshore Passenger flying is harder on the aircraft than Logging work?

Not at all. Columbia have lost a 234 in South America in the last year or two. I'm sure there have been other incidents too.

With no jibbering ballast in the back, logging accidents don't hit the headlines in the same way as offshore accidents.

If we look at the history of S-61 accidents then the ones in the back may not be the biggest issue. Two other things are going on.

The 234 stood out because it carried a lot of passengers and put a larger number of people at risk in a single event.

The Super Puma stands out because it has been the dominant offshore passenger carrying tool in the internet age when the outrageous views of the ignorant carry more weight than informed alternatives.