AS350/H125 Hydraulic related accident statistics

[jellycopter]

Does anyone know if there is a database available that details AS350/H125 hydraulic-related accidents. I'm interested in training incidents as well as the real thing. In particular, if anyone has any knowledge of hydraulic servo runaway or seizure (slider valve seizure) on the AS350 series, that information would be very useful. I'm not interested in servo transparency/jackstall incidents (ie Colin McRae). Thanks. JJ

[John R81]

In the UK, the AAIB search facility (https://www.gov.uk/aaib-reports) can be used with aircraft type and key-word search

[nigelh]

Hi Jelly .... I would guess that almost all of the 350 Hydraulic accidents have been as a result of training !!
it would be so much easier , I would have thought , to just put two systems in there and stop all hyd off training ... then no more write offs !

[SASless]

It is a very poor design in my opinion....far too many Pilot Traps in the way the system is controlled and operated.

But then....there's lots of "cheap" about that aircraft type.

[nigelh]

Sas ....not sure I agree with that . The systems are pretty straight forward ( if you are talking about the sequence of cutting off hydraulics for training ) and if you can't get that right maybe you are in the wrong job !!

[tqmatch]

From both an engineering point of view and piloting, the Hyd system is simple and robust, and from most of the reports I've managed to locate, a high proportion of the hyd related incidents are training related. I think the biggest "gotcha" has to be lack of knowledge as to "why" we drill the way we do, and the need to consider the yaw compensator. I know from personal experience how easy it is to get behind the aircraft and be tempted to flick the hyds back in, but quickly reminded that this is a bad idea!

[HeliboyDreamer]

be tempted to flick the hyds back in, but quickly reminded that this is a bad idea!

I don't know anything about the 350 but would be interested in understanding what you mean above. Can you explain further or direct me to some technical reading on the matter?

[jellycopter]

"I know from personal experience how easy it is to get behind the aircraft and be tempted to flick the hyds back in, but quickly reminded that this is a bad idea!"
I'd welcome an explanation of that too. I know the controls suddenly become lighter and can initiate a momentary left roll, but surely it's better to regain control than fight it to the scene of the accident?
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[nigelh]

Especially if you release pilots pressure at the same time as flicking back on . I wouldn’t hesitate if I say my aob increasing together with more cyclic pressure !!

[SASless]

Nigel, If the system on the 350 is so good....why so many accidents both operationally and in training??

Why are we even having this discussion?

How many buttons, switches, levers are involved in controlling system as compared to other aircraft?

The Chinook with two flight control systems had one three way switch.....System 1, Both, System 2 ..... which is typical of most dual system aircraft.

[nigelh]

It’s all to do with the accumulators . You don’t want to have hyd assistance in one plane without it in the other therefore you have to have them all topped up before you re set to Hyd on ... that works both ways so you cut Hyd off before the are depleted when doing a training exercise . Others can explain better then me but that’s basically how it is . The accumulators give you about three stirs of the cyclic giving you time to come back to around 60-70 knots then they will run out ( but not necessarily at exactly the same time )

[JimEli]

From both an engineering point of view and piloting, the Hyd system is simple and robust, and from most of the reports I've managed to locate, a high proportion of the hyd related incidents are training related...

With the exception that the hydraulics are a low pressure system that can be overridden by flight loads, powered by a belt that was susceptible to breakage, switches confusing labelled HYD TEST, updated to ACCU TEST, which on several occasions being mistakenly confused for the landing light switch, but now incorporating a guard, initially and ridiculously bi-stable but finally mono-stable switch, having another switch labeled HYD CUTOFF but variously named something else throughout the RFM, the same switch having an alternate function under a dual-hydraulic configuration, a caution panel with a single annunciator for both systems, later modified to individual annunciators and a system that allowed depressurizing the tail servo and yaw load compensator without a warning in the cockpit...

I find it difficult to call the hydraulics anything but a human factors nightmare.

[nigelh]

I guess when you put it like that ......!!! Apart from that the hydraulics are fine !

[Mee3]

sasless being sasless. Cannot take a chance off having a cheap slap on EC. How many of these accident pairs a failure with a pilot error during pre flight check?

And Jim, how many of those belt lost was ignorance during maintenance? Might as well install an anti gravity. Shouldn't we been trained into our muscle instead of read FM at the very moment?

[SASless]

Care to answer the question about the various controls, knobs, buttons, levers.....etc for the 350's hydraulic system....and say compare and contrast that to a Jet Ranger series or Bolkow/MBB machine?