Helicopter crash in Norway today
 

AS350 LN-OFU. Just speculating: jack stall / servo transparency ?

There you go....case solved.....Jack Stall caused it!

That was a new PPRuNe Record time for the cause of an accident being determined.:ugh:

TD.....you better pull. out your Webster's and read up on the definition of "speculation".

Ok, will look up speculation.
 

Not sure how you jump from "just speculating" to "case solved". CFIT is a plausible cause here. A mechanical problem not induced by the pilot is pretty unlikely for a 2 month old helicopter.

in my experience, it's the new ones that have the teething problems...

Godspeed to them all

Six now confirmed dead, Swedish pilot and five locals in their early twenties. Helicopter was performing sightseeing trips for festival participants.
Per

Can someone describe Jack Stall / Servo Transperancy as mentioned above. What exactly is it?
I'm guessing the servos lock up, and it can't be overridden.
Do the accumulators help on the AS350?

This topic has been discussed in detail a couple of times here at Rotorheads.


https://www.pprune.org/rotorheads/pr...ack-stall.html

https://www.pprune.org/rotorheads/25...riences-2.html

The Norwegians must offer quite the scenic tour experience if they are able to end up in jackstall.

Happens more than you think.
I had a pilot at the end of tree-planting season, giving all the tree-planters a ride of their life, high G turns, negative G pushovers, steep banks, nap of the earth stuff....funny thing when he was in view of camp, he flew like a fricken angel. Cant let the wrench see what he was doing you know.
guess he didn't realize sound travels and i could hear every twist, turn and bank from miles away.

bottom line, many pilots fall prey to giving the passengers a ride to remember...if they survive.

Mechanics (Engineers for those who prefer that title) have done in many a Pilot and Passengers too....so what is your point re this particular tragedy?

Problems that can cause a crash? I think not.

The 350 however, is infamously known for what jymil suggest regardless of what you and others might say and have caused several accidents with multiple deaths. One of the more profiled accidents happened in the Grand Canyon in 2003 and the pictures/video collected from the pax's cameras is the reason the Appareo Vision 1000 comes standard in these helicopters today.

Bell_ringer,
Not at all if you know what you're talking about.
The American pilots are also able to provide quite a ride, and there are examples from the rest of the world too.
https://www.pprune.org/rotorheads/10...ce+helicopters (link to the above accident)

Here's a link to another accident with same outcome from Norway being discussed here.
https://www.pprune.org/rotorheads/62...y-today-2.html

For the ones that have got the proper training in the 350, this is old news and is easily avoided.

Kulwin Park,
The short explanation is: when you load the disk beyond the capability of the Hydraulic system, the controls lock up. It disappears as quickly as it comes when the severity of the manoeuvre is reduced. A 350 doing high G manoeuvres at high speed and close to AUW it is really easy to get it in, and one must have sufficient clearance to obstacles in order to recover.

Now, of course it can be a lot of other reasons for this crash.

It's a sad loss regardless the cause of it!

Cause a crash? Google west Franklin s92

Nubian,

Question.....if the 350 is known to have a hydraulic system that can be overcome by feedback forces and thus allow a loss of Pilot control of the aircraft.....why has that not been addressed and modifications made so that the flight control system can function under all flight conditions the aircraft can be expected to encounter?

From past discussions here at Rotorheads, it was noted one particular manufacturer seemed to design aircraft that had that flaw.

From discussions about LTE....again we see one maker that seemed to overlook that problem in their aircraft until it became a PR problem that affected marketing.

What role should the certification authorities play in this?

I guess that is really two questions...one re the manufacturer and the second being the certification authorities.

All onboard now confirmed dead. One died in hospital, and one was missing for a while. I guess that's where the "2 survivors" came from.

But you have to be properly ham-fisted even at High AUM to generate the sort of feedback forces that will stall the jacks - and you have to hold it in the stalled condition since it is almost self correcting if you ease off the load.

the stats dont back this up at all, at least comparatively from one profession to the other.
you're a smart man, you figure it out without speculating.

This is the last aircraft I dealt with that involved servo transparency, he ran out of time and space, like most of these scenarios as they repeat themselves.
The TSB report details some good info that answers some questions or accusations here.

http://www.bst-tsb.gc.ca/eng/rapport...5/A16P0045.pdf


"According to Airbus Helicopters, the phenomenon of servo transparency can occur “during excessive maneuvering of any single hydraulic system equipped helicopter, if operated beyond its approved flight envelope.” The manufacturer does not consider servo transparency a failure of the system, but a limitation of all single hydraulic systems. Unlike in the case of a hydraulic system failure, there is no visual or aural indication to alert the pilot that the hydraulic system is approaching servo transparency...."

SAS,

Well, although the type has a reputation, it is worth to mention that it does not happen without exceeding limitations in order to experience it, but to do so is fairly easy.
To answer your first question: The manufacturer has addressed the problem with information on the subject. Airbus (back then Europcopter) published this: https://www.airbushelicopters.com/we...-03-REV0-A.pdf
In order to give proper training required to recover from servo-transperancy you need to exceed the limitations in some way, so it is a bit of a Catch 22.
Now, what do you do when pilots exceeding the limitations and get into trouble? Redesigning the helicopter?

As to your second question, I don't agree that the manufacturers necessarily is overlooking the problems as what I already has said about exceeding limits. As for the certifying authority could look at it in a way that the limit for getting into this phenomenon is too low and come up with some type of sanction, if they deem it to be a significant problem. It has certainly caused a few deaths, but if that is due to lack of training is the question I guess.

A simple hydraulic pump drive failure?
 

It was very obviously caused by deep vein thrombosis (DVT).

Jack,

The new belt is alot more reliable than the old belt thats for sure
the pump/pulley assembly is vastly improved, although the bearings had some growing pains.
it is rare to suffer hydraulic failures now compared to years ago, but isn't impossible.

I also see, if the identification of the aircraft is correct, its a B3e, so it has dual hydraulics and dual pumps, one being direct drive off the MGB.
While the dual hydraulics have an overload sensor to warn you of impending servo transparency, it can be missed or ignored, it doesn't stop you from flying into the servo transparency
the final outcome of this accident will be an interesting read, but I fear it's just history repeating itself.

Is the dual hydraulics now standard on H125/AS350B3e ? I thought it was an optional item for the single engine squirrels.

How Old was this B3?
 

I flew both the B2 and theB3 in Phoenix, AZ more then 10 years ago. At that time there were issues with the belt drive system. Neither bird was equipped with the dual hyd system.

this is true, dont they call it the gross weight increase kit or something??
Either way, Ive only ever seen b3e's with dual hydraulics. I thought wrongly that everyone wanted dual hydraulics for the safety aspect.
the picture i found of this aircraft showed otherwise (swashplate boot visible). So unless someone can confirm otherwise, the belief is this a/c had single hydraulics.

The 355 with Dual Hydraulics could STILL see "Transparancy," The machine even has a "LIMIT" light that triggers when near, ufortunately I don't have enough time in single engine 350's to verify if they all do too, I know the B3e does...

It will give you an increase in internal GW, but not for external loads so for a utility operator it does not make sense to pay lots for the extra weight of the kit, reduced payload and increased cost of operation (TBO of the MGB is reduced with this kit due to the extra mechanical drive from the MGB.)

Jack,

The machine was just a few months old.

https://aviation-safety.net/wikibase/228643

if you read the report in the link given above, it does say that the dual hydraulic system in the B3 cannot easily be retro fitted to the B2 helicopter built with the single system, and that the single system has NO warning light, whereas the dual system does.