I don't think so - the only way to recover is to reduce the severity of the manoeuvre.

Just hovering a squirrel with the hyds out for a short while is tiring enough but it would take a lot of brute force to handle the aircraft at 120 kts.

The type of relatively benign manoeuvre that could catch out the unaware is a descending right hand turn which is tightened up using lever and/or aft cyclic - the tendency of the aircraft to pitch up and roll right would roll the aircraft towards the inverted which could be interesting close to the ground.

Strange that Eurocopter now say it is OK to repeatedly stress an aircraft teaching ST because that is the reason they stopped us teaching jackstall on the Gazelle - repeated stress fatiguing the rotor system.

Kinda like this:

Not an AH1T and not at high speed but maybe this brought the pilot close to the extremity of the a/c's cyclic authority.

Anthony

Your video shows an aircraft almost getting dynamic rollover, not the same as servo transparency. Good video though.

Yes am aware its a different situation.

Your video "nails it" as you would say over there and it makes me a little weary of the Eurocopter. I mean you should be able to perform a zoom like that without the thing losing aerodynamic stability. The way the tail hangs down (I'm guessing that's the loss of pitch) is concerning.

The possible servo transparency happened in the turn onto a long final, banking steeply to the right (60-90 degrees according to eye witnesses) with a relatively high speed. Ground speed from GPS is given as 120-125 kts.

The forward speed at ground impact has been calculated to about 105 kt based on tracks at the accident site. The helicopter hit the ground with a nearly flat pitch angle and about 45° of bank to the right. It came to rest about 25 meters past the first point of impact.

I have not seen any gyrations mentioned, it entered a steep descend while still banking steeply, but rolling out somewhat before impact.

From the report:
Extensive damage to the main gearbox and main rotor system indicated high torque when the helicopter collided with the ground. The position of each of the three servo control actuators could be determined, and these corresponded to a control position that would give a significant bank to the right.
But also:
The positions of the servos were probably affected by the impact, as was the cyclic stick, and they do not necessarily correlate with the positions of the flight controls prior to the crash.

Reducing the severity is definitely the FM recommended way of recovering. But in this case it is possible the pilot ran out of altitude in an awkward attitude, and in that case the last thing on ones mind may be to reduce the severity. Especially to lower the collective.

I have not seen anywhere how the control forces experienced in servo transparency and those during a total loss of hyd power compare. I would have thought that with a total loss of hyd, the pilot has to do all the work, while in servo transparency he only needs to put in "a little extra". The FAA test flights from 2003 mentioned in 1.18.2 (page 33-34) in the report shows a diagram of the lateral control forces required.

The data that form the basis for the diagram show that the forces on the collective were between 3.5 and 10 daN (not shown in the figure), while the cyclic was pushed to the left with a force of between 2.5 and 12 daN.

They have the really annoying tendency to loose tailrotor in flight. Therefore emergency AD, limitations to Vne, manuvering and inspections every 3 hours.

Today is not a good day to own shares in Eurocopter. I´m sure they will fix these problems but it may take a few months.

EASA Airworthiness Directives Publishing Tool

From the AS350 AFM chapter 3:

Actuate the switch on the collective pitch control lever, to cut off hydraulic pressure.
Load feedback will be felt immediately ; load feedback may be heavy if the helicopter is flying at high speed :

. collective pitch : 20 daN (44 lbs) approx. pitch increase load
. cyclic : 7 to 12 daN (15 to 26 lbs) approx. left-hand cyclic load
. cyclic : 2 to 4 daN (4 to 9 lbs) approx. forward cyclic load
. yaw pedals : practically no load in cruising flight.

So it seems at least on the cyclic, it can get as bad as a full hydraulic loss (12daN).

I am really surprised that the AS-350 series was successfully certified with published control forces so high. Even after a single system failure (Hyd or Servo transparency) the resulting control forces must not exceed those outlined as Arm strength N (lb) Design criteria levels in Chapter 14 of the US Federal Aviation Administration Human Factors Guide. Table 14.5.2.1 of this guide clearly states the maximum force for a right hand, lateral control motion to the left should be no more than 6 to 8 pounds. This is far in excess of what is published in the AS-350 RFM. US designed and certified aircraft are required to meet these requirements. These standards were applied when Sikorsky included viscous cyclic control dampers in the H-53 Series to insure that in the event of a control damper bind it could be easily over ridden within the force limitations of the aforementioned table.

My bad the 6-8 lb limit was for a right hand control motion to the RIGHT, the back hand direction of motion.:rolleyes:

Spot on!

I think this report is almost identical to the accident of Colin McRae a few years back.

A result from showboating around without leaving sufficient room to recover if things not go as planned.

My thoughts. Hence the cross link when asked to explain JS

After the accident the involved operator introduced manoeuvre limitations on flights with passengers:

... Roll and pitch angle during passenger flights
Maximum roll and pitch angle during operations with passengers on board below 500’ AGL is set to 30 degrees roll and 15 degrees pitch.

... Initiating a right descending turn at low level
Initiation of a right descending turn at altitudes below 500’ AGL with passengers on board without first lowering the collective is prohibited.

That will probably make it safer for the passengers (of that operator), but what about the rest of us?

If I interpret it correctly, the EASA OEB recommended method of training servo transparency should be included in (all?) AS 350 training in Europe. The report seems to indicate that this has not been too well known. It would be interesting if anyone knew if:

• It has made its way into the syllabi of the flight schools?
• It is tested during Skill Tests / Proficiency Checks? (should it?)
• Operators include this training in their OPC's?

And finally, my view is that it could be asked if the training method is adequate. (The accident pilot had been through ST training) Training is important mainly to teach pilots where the limit is and how to avoid it, but also to recognise it and intervene early if it should still happen.

It could be said that the approved method with a demonstration of ST in a diving left turn is confidence building, and reinforces the feeling you get from reading the statement in the FM that the phenomenon is self-correcting. (Rolls back towards level and the nose pitches up. The collective goes down - and you are out of it.) Could that give the impression that this is really no big deal?

If the demonstration was done in a diving right turn, it could, if AAIB and AIBN are correct, be a more violent thing. As I understand it, the turn would then tighten both by an increase in bank and a pitch up. As the collective drops at the same time, rate of descend increases. If you try to roll out to the left, you would load the servos even more. Experiencing this during training would perhaps get the pilots' attention and indicate that it not always self-correcting, at least not if you are in a right turn in a tight spot.