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Old 19th Dec 2012, 10:32   #81 (permalink)
 
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I don't think the AS350 is the only type that's ever suffered from servo problems, eg cyclic hardover etc.
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Old 19th Dec 2012, 13:19   #82 (permalink)
 
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Can't you guys stopping speculating on the unknown or shall we remove the first 'p' of PPRuNe?
Not posting often here, but really tired of reading post from self-called professionals...
Keep the rumour mill turning, but for god sake stop the speculation going a one way strret when we all know that most of incident/accident are happening when more than one hole of the swiss cheese align...
Good day
Kami
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Old 19th Dec 2012, 18:37   #83 (permalink)
 
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Kami - historically a great deal of the speculating done on these pages has turned out to be surprisingly accurate come the final publishing of the Accident Report - despite protestations from others.

This is, after all, a virtual crewroom and therefore both informed speculation and wild-ass guessing are acceptable

Last edited by crab@SAAvn.co.uk; 19th Dec 2012 at 18:38.
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Old 19th Dec 2012, 19:01   #84 (permalink)
 
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It seems pointless to keep urging people not to speculate after a crash for it is the most common (you could call it natural) thing for pilots and engineers to do.

We all know that nothing is definitive until the report is out so, those of you getting upset about other people's opinions should try and pipe down a little.

I don't think anyone has come out saying "this is the absolute cause of the accident" so, live and let live.

These suppositions are what many are interested in reading about and, as CRAB has said, a good many professional guesses have incidentally proven correct in the end, meaning that such idle gossip might not be all bad after all.
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Old 20th Dec 2012, 01:09   #85 (permalink)
 
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Thank you Crab and Anthony,
May be my past participation to a few 350 accident investigations made me more cautious than I should in this forum. I am not in anyway saying that it cannot be a servo issue, but I have learned the hard way that not keeping a clean brain just hamper your ability to find the real root causes and may lead to improper hasty/easy conclusions.
I'll wait and see how it develops.
Fly safe
Kami
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Old 20th Dec 2012, 06:17   #86 (permalink)
 
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Why is Hyd problems even on the table here? Does anything in this accident point in the direction of a Hyd problem? In the picture of the aircraft it looks like controlled ditching, and with a hyd problem you donīt ditch in the water..
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Old 20th Dec 2012, 07:01   #87 (permalink)
 
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MRotor - you are making a lot of assumptions about the skill level, experience and currency of the pilot.

It may be possible that a hyd failure (given the heavy pedal loads hyd out on the squirrel) might be misdiagnosed as a TR problem, especially at night in sh*t weather over the water (not in everyone's comfort zone).
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Old 20th Dec 2012, 07:08   #88 (permalink)
 
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Maybe so, but if you get a hyd problem you get a red HYD light in the panel..
This is also required training on PC/OPC every 6 month. I was just wondering what in this case point in the direction of a hyd?
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Old 20th Dec 2012, 08:17   #89 (permalink)
 
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MR - to be fair, the more we hear about this sad accident, the less it looks like hyd failure/servo transparency but it was brought up at the beginning of the thread by a very experienced test pilot and investigator - it should still not be totally discounted, especially as a contributory factor.

A hyd failure might be easy to diagnose and manage on a PC/OPC when you know it is coming and during daylight - it would be a whole different ball-game at night in poor weather when you were already working hard to keep orientated.

Last edited by crab@SAAvn.co.uk; 20th Dec 2012 at 08:17.
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Old 20th Dec 2012, 08:27   #90 (permalink)
 
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Quote:
It may be possible that a hyd failure (given the heavy pedal loads hyd out on the squirrel) might be misdiagnosed as a TR problem, especially at night in sh*t weather over the water (not in everyone's comfort zone).
...but this accident happened at daylight in good WX!
And the official statement of the BFU-inspectors was, that the T/R driveshaft failed. And i think, that they should be able to determine wether the shaft broke in flight or at the impact on the water surface. Just my 50cts....

skadi

Last edited by skadi; 20th Dec 2012 at 09:38.
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Old 20th Dec 2012, 09:33   #91 (permalink)
 
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Quote:
It seems pointless to keep urging people not to speculate after a crash for it is the most common (you could call it natural) thing for pilots and engineers to do.
And rightly so. Pilots want to know immediately if there is something dangerous about the helicopters they fly and how to minimize the risk. Anything that can help to make it safer to fly until the actual cause is found is welcome.

The main interest of the manufacturers is to blame the pilot and continue selling their helicopters. Now new AS350 have dual hydraulics despite many crashes over the years due to hyd failures. It did take about 35 years to make the aircraft safer.

Hydraulics may not have been the cause to this crash. But it has been the cause of many AS350 crashes. Many during training and some due to failures.
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Old 20th Dec 2012, 10:02   #92 (permalink)
 
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Skadi - apologies, I was misled by earlier posters about the time of day and weather.
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Old 20th Dec 2012, 10:04   #93 (permalink)
 
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It seems there may be some correlation between AS350 accidents and poor visibility and I am now speculating (sorry but I am) as to whether this is something to do with servo-transparency?

Having never had ST in a Squirrel I don't know how it feels like but - if a pilot induced a rapid rate turn with moderately high G in order to avoid IIMC perhaps he could encounter this and, if unfamiliar with it "freak out"?

What with servo transparency (which apparently doesn't happen in some helis) and a history of hydraulic system failures plus the current tail rotor issue on the new B3e - I am beginning to lose a little confidence in the 350.

I hope I am wrong because this type has become one of the most popular singles on the planet!
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Old 20th Dec 2012, 10:08   #94 (permalink)
 
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Skadi-...thx my point exactly.

I agree, it has been alot of accident due to the HYD system in the AS350, but I the new AS350 still comes with a single hyd system, with a dual system as an option. Because of the weight issue I belive alot of operators still will bye this helicopter with a single system. So fly safe with this "problem" in the back of your mind if you fly the AS350..

Fly safe

MRotor
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Old 20th Dec 2012, 12:14   #95 (permalink)

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Quote:
Having never had ST in a Squirrel I don't know how it feels like
You should be so lucky, ducky!

Cheers, ST.
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Old 20th Dec 2012, 12:49   #96 (permalink)
 
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And there I was thinking you didn't care!
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Old 20th Dec 2012, 17:53   #97 (permalink)
 
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ST is not the major problem. Lose hydraulics on a 350 and you will be as busy as can be.

·
Simulated Hydraulic failure


(


Except EC 130 B4 & AS 350 B3 equipped with the optional dual hydraulic system):


- In steady flight conditions, simulate the hydraulic failure by depressing HYD TEST push button on the
System Control Unit (


Honeywell or SCU console panel): HYD + Gong sounds to be able to achieve Vy,


CAUTION


: The Instructor must insist to obtain speed reduction before the HYD cutting off.


- The intensity and direction of the control feedback force will change rapidly. This will result in a loss of
control,
- Control loads increase with speed. As control loads increase, be careful not to inadvertently move twist
grip out of FLIGHT detent,
- If necessary during the training exercise, hydraulic assistance can be recovered immediately by setting
back HYD TEST pushbutton to OUT position or by switching back the hydraulic cut-off switch to ON,
- If the HYD TEST pushbutton is not reset on the SCU, no hydraulic assistance can be restored. After
hydraulic cuts off with the switch on the collective lever, do not forget to switch off the HYD pushbutton on
the console.
- Once safety speed set, reset HYD TEST pushbutton to restore hydraulic pressure in tail rotor
accumulator (AS 350 B2/B3).
On previous versions of AS350 equipped with a HONEYWELL console control, do not silence the HORN
by using the HORN switch.
The HORN will be silenced when the pilot selects the hydraulic cut-off switch to off.
If the pilot uses the HORN switch to silence the HORN before using the hydraulic cut-off switch, this
crucial step could be forgotten. This could then result in significant unbalanced lateral cyclic feedback
forces, especially at low speed, if one of the lateral accumulators depletes before the other one.
In addition, de-activating the HORN using the HORN switch, makes it unavailable to warn the pilot of low
or high rotor RPM.
Pay attention to the following:
- Hydraulic accumulators gives energy during approximately 20 seconds, so reduce to safety speed
in this time delay,
- Do not accelerate after switching OFF the hydraulic cut-off,
- Anticipate to perform a shallow approach,
- Perform a running landing,
- Hover flight or any low speed maneuver must be avoided,
- Keep in mind that All Up Weight increase risks of aircraft control loss at low speed,
- The statistics show that a non strict compliance with the procedure increases the level of risk in a

consequent way

Last edited by Gemini Twin; 20th Dec 2012 at 17:57.
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Old 20th Dec 2012, 19:46   #98 (permalink)
 
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Sultan . As Arm out of window says ... The 350 is very flyable with no Hydraulics . I had one for 10 years and regularly did approaches , landing and hovering . This really would not be a problem for a cpl in my opinion .
Lets hope we find out soon .
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Old 20th Dec 2012, 20:36   #99 (permalink)
 
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I don't know what you're getting at with the 'busy as you can be' thing, Gemini Twin - what you've put there is a few simple actions and some notes, and is really a very simple procedure.

Simulate with the test switch.

Slow to a safe speed if required.

Activate the collective-mounted hydraulic isolate.

Reset the test switch.

Plan and fly the landing - usually a shallow approach and run on with a few knots.

To say it's difficult is very misleading.
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Old 21st Dec 2012, 08:05   #100 (permalink)
 
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Not to say even easier for the actual emergency which is basically:

-Set IAS 40-60
-Collective HYD switch OFF
-Shallow approach

Doesn't sound too difficult does it? I am probably weaker than the average pilot, and I have no problems handling the 350 HYD off. And since we train on this every 6 months I'm not losing any sleep over flying the 350. So can we move further HYD discussions to the 350 Hyd thread until there is actually any indication that this was caused by HYD problem? So far there have been none.

To sum up what we actually know about this case:

- the aircraft seems to have made a successful forced landing into the sea
- the occupants have made it out of the helicopter
- preliminary findings point towards possible t/r driveshaft failure
(I find it hard to believe that investigators wouldln't take into account the forces on the driveshaft when impacting the water, so to me it sounds they have evidence this failed prior to impact with the surface)
- the accident happened in day VMC

I'd like to thank Skadi for keeping us up to speed during the search for the helicopter, and for keeping us up to speed on local newspaper articles about the accident. Thanks!

Tom

Last edited by TomAndreas-NOR; 21st Dec 2012 at 08:14.
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