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North Sea heli ditching: Oct 2012

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North Sea heli ditching: Oct 2012

Old 24th Nov 2012, 17:18
  #561 (permalink)  
 
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Yes. Right on! I vote for a new shaft without any weld, except that it would take years to certify.
Except that the 332l has been flying with a welded shaft for over thirty years.
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Old 24th Nov 2012, 18:51
  #562 (permalink)  
 
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Of course. However in the 332L and L2, it was subjected to lower torque and consequent bending/flexing/vibrations?/whatever other manifestations of stress might exist.

The EC225 seems to have reached the limiting threshold for welding in this application.

(Edited to add this genius idea.) How about thickening and extending vertically the wall of the lower shaft, at the top where it meets the upper shaft, cutting a screw thread into both shaft sections with suitable radii to minimise stress risers and screwing the shaft sections together?

I think I'll apply to be a consultant for Eurocopter. All I'll ask is Euro 250k per annum and little perks, like a comfortable pension.

Last edited by Colibri49; 24th Nov 2012 at 19:07.
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Old 24th Nov 2012, 20:00
  #563 (permalink)  
 
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Long bolting could be worth a look but screw threads on the component mess up alignment and are not useful with gearing.

Last edited by jimf671; 24th Nov 2012 at 20:02.
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Old 24th Nov 2012, 20:10
  #564 (permalink)  
 
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However, it is funny how the welded shaft was fine for the first 120 or so EC225 aircraft and 75,000 hrs just in the Bristow fleet.

Last edited by HeliComparator; 24th Nov 2012 at 20:11.
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Old 24th Nov 2012, 20:41
  #565 (permalink)  
 
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However, if I was a gambling man I would put money on the next accident NOT being related to a Super Puma family gearbox issue. By the time we resume flying it will surely have had more scrutiny than just about anything else! Something unrelated will come out of the woodwork on that or another type.
HC,

I think you are a brave man to make such assertions. Maybe, just maybe all the Super Puma MGB issues are the symptoms of a more fundamental sickness. If so the regulatory/investigative diagnosis must be absolutely thorough. Otherwise EC will be reaching for the first aid kit when only major surgery will cure this malady. I desperately hope your feelings are based on hard fact not blind faith.

Colibri,

The day they let a pilot design a helicopter gear box is the day I stop sitting in one. Screw threads are for bottle tops, not holding shafts together.
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Old 24th Nov 2012, 20:51
  #566 (permalink)  
 
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Yes thats a puzzle... apart from the change in the countersinking of the hole -maybe they changed supplier ?
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Old 24th Nov 2012, 21:00
  #567 (permalink)  
 
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Screw threads

Droopystop, quote " Screw threads are for bottle tops, not holding shafts together".

Or rotor heads?
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Old 24th Nov 2012, 21:07
  #568 (permalink)  
 
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FERetd,

How many heads are screwed directly onto the shaft, ie the axis of the screw thread coincides with the drive shaft axis and the torque is transmitted throught the threads?

Last edited by Droopystop; 24th Nov 2012 at 21:08.
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Old 24th Nov 2012, 21:28
  #569 (permalink)  
 
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Droopystop, maybe they are all a symptom of fundamental sickness. Maybe the gearbox internals are made of cheese, just like the moon? Maybe a mouse got inside to eat the cheese?

On the other hand, perhaps you are just over-reacting to a very successful transmission design that has had 2 problems. One catastrophic (L2) the lack of an exact explanation for which does make me uncomfortable until I remember the 3 million flight hours that the identical design has flown without a problem, and that it probably wouldn't have happened if correct maintenance procedures had been followed. And recently, the other problem rearing its head which is non-catastrophic but we suspect the result of a design change. Hardly an indication of fundamental sickness unless you are determined to exaggerate the problem.

The S92 churning events were of similar severity to the shaft breakages, requiring an immediate landing. Ditto the vespel drive failures which required an immediate landing according to the RFM of the time. The difference is they didn't happen in UK waters and you have forgotten about them!
Clearly the gearbox is not perfect, but it is no more imperfect than any other helicopter.

Last edited by HeliComparator; 24th Nov 2012 at 21:30.
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Old 25th Nov 2012, 01:46
  #570 (permalink)  
 
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Ditto the vespel drive failures which required an immediate landing according to the RFM of the time.
Sorry HC, but you are wrong. The S92 RFM has always had a Land Immediately requirement when the MGP Oil Px is below 5 psi. A single vespel spline failure/oil pump failure did not produce an Oil Px indication below 5 psi.

Also the first churning event produced a number of (startling) indications that resulted in the crew electing to carry out a forced landing, however it was not an RFM instruction but an airmanship decision.
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Old 25th Nov 2012, 03:04
  #571 (permalink)  
 
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it was not an RFM instruction but an airmanship decision.
Correct insofar as the decision at the time was airmanship based, but actually with the smoke in the cabin the RFM did say "Land Immediately." You may recall that SAC wanted to remove that line subsequently!

Anyway, back to the 225.......
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Old 25th Nov 2012, 06:48
  #572 (permalink)  
 
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so what is being used now in place of the 225s, have the old tigers had a call up, sorry if this has been answered
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Old 25th Nov 2012, 08:16
  #573 (permalink)  
 
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Well irony of ironies you know that Italian machine that had a tail boom that kept falling off? Well guess what? It is now doing a sterling job in certain parts of the North Sea flying up to 10 hours per day taking up the slack.
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Old 25th Nov 2012, 09:56
  #574 (permalink)  
 
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Bottle tops?

Droopy, now you are just nitpicking.

The reason that your rotor head stays where it should is because of the friction provided between the threads of the "Jesus" nut and the main shaft. The torque is transmitted by the splines - but you knew that.

If, quote:- " screw threads are for bottle tops", try flying your helicopter without the "Jesus" nut.

Good luck!

P.S. The B747 trailing edge flap drives are of "bottle top" design - works well.
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Old 25th Nov 2012, 10:35
  #575 (permalink)  
 
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FER - listening to too many urban myths! Jesus nuts are fitted to ancient teetering-head helicopters, not to modern articulated head ones.

Last edited by HeliComparator; 25th Nov 2012 at 10:36.
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Old 25th Nov 2012, 10:41
  #576 (permalink)  
 
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HC,

I genuinely hope you are right and I am over reacting. If these three incidents are the only gearbox malfunctions ever experienced by the Puma family then I certainly am and stand corrected. All I hope is that EC catch all their mice so we can sit back and know the MGB is going to work every time, all the time. And that goes for every helicopter manufacturer.

FERetd,

As you point out the thread on the Jesus nut (although big helicopters have a lot more than one) doesn't transmit torque. Colibris solution appears to have a thread that transmits torque, just like a bottle top.
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Old 25th Nov 2012, 12:00
  #577 (permalink)  
 
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VL, perhaps it was before you did your 92 course, but in 2005 before the Norsk vessel spline incident, this is what the S92 RFM said verbatim:

start quote:

MAIN GEAR BOX OIL SYSTEM FAILURE

Symptom:

MGB OIL PRES or MGB OIL HOT or MGB CHIP or ACC 1 CHIP or ACC 2 CHIP

CAUTION
The main AC generators are cooled by main gearbox oil. Loss of cooling oil may result in mechanical failure of the generators and loss of main electrical power.

Confirming:

Main gearbox oil pressure is less than 35 psi, or*
Main gearbox oil temperature is greater than 130 degrees.

Action:

1. Descend to minimum safe altitude.
2. APU - ON
3. APU GEN - ON
4. Land as soon as possible.

If the MGB OIL PRESS warning indicator also illuminates:

1. MGB OIL BYPASS switch - BYPASS

WARNING
BYPASS must be selected within 5 seconds after the warning indicator has illuminated to ensure an adequate quantity of oil remains in the gearbox. DO NOT activate BYPASS if the warning indicator is not illuminated.*

2. Land as soon as possible.

If MGB oil pressure continues to decrease or there are loud/unusual noises, unusual vibrations or progressively increasing power required to maintain flight:

3. Land immediately.

end quote

So, pressure falls below 35 psi, button is pushed, pressure continues to decrease down to a little over 5psi ("continues to decrease" being the operative words) then it is land Immediately. The mention of 5 psi was only added after this event.

Last edited by HeliComparator; 25th Nov 2012 at 12:02.
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Old 25th Nov 2012, 12:18
  #578 (permalink)  
 
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HC.....could we avoid going back through another rehash of bashing the 92 and just stick to the issue at hand. The 225 MGB problems has effectively grounded the aircraft, destroyed faith amongst its passengers, and caused a hell of a disaster for the Operators and Customers.

The cause of the problem, the cure for the problem, and whether the reputation of the 225 can be salvaged....are what needs to be discussed.

We are not here to compare the 92, 225, and 139 to each other.

We are here seeking answers to the problems extant for the 225, EC, and the Operators.

I know it must be annoying to see the 92 prevail over the 225 as you certainly had a lot of "stock" in the 225 and spent a great deal of time talking down the 92 while extolling the many virtues of the 225 as you saw them then.

So....when can we expect to see some resolution of this problem with the 225 MGB? What effect has this had on the Operator's profitability? Are the Operators going to file suit against EC? What is EC's Liability here? How bad has the damage to the 225's reputation has occurred? Tell us your thoughts on those issues and leave off harping on the 92 please.
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Old 25th Nov 2012, 12:36
  #579 (permalink)  
 
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SAS, yes I agree it seems to be going off topic, but my point is that although the spotlight is on the 225/L2 at the moment, it has also been on other modern types such as the 92 in the past for events of the same severity. In part the spotlight was less bright because these events didn't happen in CAA-land.

Yes I am saddened to see the 225 taking a beating because I know just what a good aircraft it is, always accepting that all helis have their issues including this one! But those specific issues aside, it is overall a really good pilot's machine with better range/payload than the competition.

It's interesting to review the S92 EOP and see just how clunky it is compared to the Super Puma family.

Anyway, regarding your specific points yes it is bound to affect profitability in the short term. I suspect that EC's liability in law goes no further than the purchase cost, since consequential losses are always excluded in sales contracts. You wouldn't buy a new car and then sue the manufacturer if it broke down on the way to work and you lost a day's pay.

Yes it's reputation has obviously suffered but hopefully this is only a short term issue and in 5 years time it will all be forgotten, just as its competitors' major events have been.

As to resolution timeframe, I know no more than you do which is that the current thinking is February.
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Old 25th Nov 2012, 13:34
  #580 (permalink)  
 
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HC Just like the Chinook after Sumburgh?
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