Hi gents, the freezing control problem with the Astar, from what I have been teach during my initial, can be created by negative G because of the pump. I have experienced it in that situation and it is not really confortable situation.
Cheers
FH

An interesting discussion. Our company employed a few senior ex army Blackhawk instructors and jack stall was a frequent topic of theirs and related a number of accidents which were a result of the phenomema. Until their employment I had never heard of the term. They also told of how it was demonstrated to pilots under going conversion onto the Blackhawk. In light of your comment Nick it would seem that an educational program may be in order.

Brian

Jack stall - Blackhawks
 

As you say Brian, very interesting indeed.

This is new to me and I suspect most others. Didn't think it happened with Blackhawks. Any chance of it with the S92?

Were there Blackhawk jack-stall accidents in Australia? I seem to recall reading that a couple of Aus BH's had a night mid-air but haven't heard of other accidents down there.

What Red Line,

From an earlier post in this thread by Nick Lappos, now ex-Sikorsky....but still somewhat knowledgeable about the issue under discussion......

"I know that Sikorsky would deem that behavior unacceptable, and require stronger servos (and swashplates, if the parts could be bent in maneuver!) I believe it is a governing philosophy of US manufacturers (certianly Sikorsky) that the controls must not lock up and the rotating control system not be damaged by virtually any maneuver the pilot can conceive, and it is a strong requirement in US Military regulations. I am also quite certain that the FAA would not approve such behavior, absent the bi-lateral agreements that make it necessary to overlook some things from foreign certifications."


Now we hear that this did occur in some Australian BlackHawks? Or is there some question as to whether it did for sure happen? Or what actually happened? I cannot imagine the Oz Blackhawks are any different than the original marks in that regard anyway.

Brian Abraham said:
"An interesting discussion. Our company employed a few senior ex army Blackhawk instructors and jack stall was a frequent topic of theirs and related a number of accidents which were a result of the phenomema. Until their employment I had never heard of the term. They also told of how it was demonstrated to pilots under going conversion onto the Blackhawk. In light of your comment Nick it would seem that an educational program may be in order."

OK, Brian. Let the education begin here. There is NO Jack stall in any Black Hawk, nor in any modern Sikorsky type. There are NO accidents caused by, related to or involving jack stall.

Maybe you could have those guys who you think said this log in and share their thoughts, I would like to discuss it with them and clear up the misunderstanding.

Nick, the guys Brian is mentioning learn to fly in Astars through the Australian military. I think there has just been a misunderstanding.

While on this subject: Does anyone remember the accident in the US where the Astar on a news job ended up crashing onto a rooftop with all of us trying to decide whether it was hydraulics or a tail rotor failure?
We all watched the footage and I was today just thinking if there had been a resolution to that accident.

Nick and Steve,
The individuals have since left and returned to the army but they were definately talking about the 'Hawk. Would seem perhaps to be one of those urban myths that develops some where and has a life of its own although they did talk of demonstrating it to students. Will try and contact one of them and see if they will post.

Brian

Nick,
An after thought. The guys mentioned read the list so your emphatic reply should give them the message.

Brian

Steve76,

I had heard rumour that the A-Star news copter was subject to the pilot mistakenly selecting the hyd test button rather than the collective mounted switch he had hoped for.

I stress that this is rumour. I have no AS350 time so am unfamiliar with the exact hyd set up on this machine, but seem to recall other A-Star incidents of a similar nature due to poor ergonomics by Eurocopter.

C'mon you guys, don't get too deep into this thing. Leave it as one of those mysterious things that can still be used as the probable cause of those un-explainable accidents that happen from time to time. You know the story, "Musta been jack stall, couldn'ta been anything else. He's too good a pilot".

On the other hand, if someone can provide real evidence that boosted flight controls commomly lock up while the particular type is being operated within its certificated flight envelope, then we need to ask some really serious question to the various airworthiness authorities who have certificated it. I would think that the FAA for example would cancel that ship's type cert in a heart-beat if this were the case.

'nuff said.


STL

Brian; that's interesting. I will be enlightning to hear what they have to say if they bother to post. I think Nicks position is pretty clear and I understand the S70 variants to have similar hydraulic pressure to the S76, (I think it's the S92 with 5000 psi?) so a jackstall situ seems surprising. Hey! next time you are at FSI, see if they will let you have a pole of the Blackhawk sim... that will put a grin on your face :)

STL - read this thread from start to finish and then re-think your post. See the light...

As to accidently engaging the hydraulic test switch:
Boost disabled, controls stiff;
Caution panel segment illuminates;
The horn blasts.

I find it hard to believe that disabling the control boost inadvertently would be more than a transient problem. The aircraft would tell you in many different ways, that the button you'd just pushed wasn't the landing light.

Had an occurence of servo transparency yesterday- cruise flight, vulture sails into path, left bank and descent, resistance to roll back to horizontal. This was not an aggressive maneuver. It's so common I barely recall the circumstances.

Devil,

Were that "engine transparency" the howls would start. That it is "servo transparency" makes it ok!

I think it is properly labeled "servo inadequacy".

Earlier in this thread I posed the question...."Why would I want to fly an aircraft that had this problem?" I also asked how the FAA granted an airworthiness certificate knowing this occurs?

Nick, you said you did not think the FAA would go for such a thing as I recall.

Does that mean the FAA is unaware of this event in the 350 series and thus the aircraft can continue flying?

What happens if someone complains to the FAA about this....will they jerk the C of A of all the 350's in the USA?

Part of the problems with servo transparency is the bilateral airworthiness agreements under which the helicopter was originally permitted to enter the country.
The helicopter was certified originally in France, and because of a bilateral agreement between France and US, if it is certified in France, then it is accepted with minimal fuss in the US for Part 27 helicopters. For part 29 machines, the process is a bit more rigorous but not much different.
The French seemed to have few problems with the servo transparency in certification, and the US was relatively powerless to not accept it (or they may not have seen this during the FAA familiarization flights).
Things like this that are discovered later in life become more a political issue than a technical issue - and political issues are nearly impossible to solve any time.
As an example of this - there is no such thing as night VFR in Europe for single engine aircraft. So the EC-120 didn't have much beyond a single wander light to light the instrument panel when it was first certified. That was caught in the approval for use in North America (both FAA and Transport Canada caught the problem) and the EC-120 had to have the instrument panel lighting changed significantly for N. American sales.

That must have been what happened with the electrics, then.

Phil

SawThe Light: have a read of the accident report I posted, link is on page 4 of this topic.

Steve76 & IHL

Took your collective advice and re-read the entire thread, my post and the TC report.

What I see is that the post is still headed "Astar jack stall" .

In my post (slightly tongue in cheek if you didn't note) I made an apparently simple observation that "if someone can provide real evidence that boosted flight controls commomly lock up while the particular type is being operated within its certificated flight envelope, then we need to ask some really serious question to the various airworthiness authorities who have certificated it." I also went on to say that the regulatory authorities would take appropriate action if someone could provide real evidence etc etc.

What's difficult to understand about that? Have you any real evidence that this has occurred while operating within the certificated flight envelope?

In the matter of the TC report here are a few notable points as follows:

- The hyd CB was likely out in flight and probably un-noticed by the crew

- The hyd belt apparently failed in flight

- The hyd test switch was activated

- The M/R accumulator pressures were less than 50% of normal pressure

- No other anomolies were noted in the hyd components

- Para 2-3 said in part "As a result of not slowing the helicopter to the recommended . . . . "

- The report said in part " The reason for departing controlled flight could not be determined. . .

Don't see anything anywhere relating to jack stall (The thread title).

STL

In subsequent interviews the pilot maintained that he had lost his tail rotor, or control. If you look closely at that crash you can see where he tried to fly it into vertical stab control, realised it wasn't happening, and deliberately flew it into the chimney to stop the whole thing in its tracks. A brave thing he did and lucky that it worked, seeing the built-up area he was over.

An AStar is quite controllable without hydraulics, and you can pick up, hover and land without them. I find it funny that there is so much criticism regarding this "servo transparency" issue as being
a failure of the French to build an adequate or safe machine, while the issue of LTE with certain Bell products is still ongoing. To be honest, I think I'd rather have jack stall than LTE any day. Until the perfect helicopter is built, there will be flaws, quirks, etc to be taken into consideration by those that fly them.

I think that the point here is that until as Nick says the problem is addressed by the manufacturer, there can be no substitute for knowledge and training.

Regarding the Limit light on the 355/365, as I understand it it is there primarily for when the machine is on the ground with no load on the head to alert to excessive cyclic displacement. You would have to be pretty severe in your maneouvring in flight to get that to light off.

The "Limit" light- at least on the 355- mirrors the servo transparency on the 350. It's not uncommon in flight.
The difference between the two situations is important. In a 350, you have inequality in control forces, and thus compromised control at an unexpected, unplanned and potentially dangerous time.
If you're in the 355, the same situation results in a light on the caution panel, and the controls remain fully effective. Hmm... so much for the blades stall and mechanical control issues....
The airframe differences between the two types are minimal beyond the power plants, electrics, and tankage. The biggest difference is the 355 has dual hydraulics and direct drive pumps. The vert stab differences probably aren't germaine.
My guess is that the servos and the hydraulics just aren't robust enough to overcome flight loads in the 350.

Regarding the hydraulic system circuit breaker- in 17 years I've only flown one (of dozens) that had CB's in place of the factory fit fuses. Remember that it requires electrical power to disable the boost...

Excellent dialouge Gents.

Here's a line from the report that may be of importance to the outcome...just as important as C/B's switches and procedures...


"There were good visual meteorological conditions at Mekatina, with clear skies, calm wind and a temperature of -30ºC.

The elastomerics tend not to be quite as "elastic" at minimum temps...giving much stiffer than normal control forces with out HYD assist.

Just my thoughts...