AS 350B2 - UnCFIT

[Hidden Agenda]

Well done Canadian Helicopters!

An incident report received today through the HAI states:

A Canadian Helicopters Ltd. AS 350 B-2, C-FQNS, was involved in heli-ski operations at Heather Mountain BC. On a fairly fast descent, in a turn, with low torque, the cyclic and collective locked up sending the aircraft into trees. Control was regained and the aircraft appeared to be okay. The group of skiers were dropped off and a subsequent flight attempted when a vertical vibration was noticed. The aircraft returned and was shut down. Inspection revealed damage to the main rotor blades, tail rotor and the right hand horizontal stabilizer consistent with a tree strike.

Thoughts and opinions? Where to start?

[Freewheel]

Where to start?

Name calling as usual!


We'll get people saying "Squirrels are s#*t", and others saying "Gee didn't it hang together well despite the abuse".


All I know is that this kind of thing is something that some will learn from and others won't. I prefer to learn, and this forum is great for that, but those that won't make it difficult at times.


Shame.

[somepitch]

jack stall? scary to say the least, glad to hear everyone walked away.

[krobar]

Felt something similar in a low-G manuevre, but not in a normal turn. How low would you have to be not to recover in time?

[MBJ]

After I experienced one in a light B2 (but at 8000ft in a fairly steep level turn) I was unimpressed by the Flight Manual treatment of the issue. As I remember it it said something vague about reducing the severity of the manouvre and all would be well! Seems more serious of a problem than that.

The controls locked for about 3 seconds on me and I was high enough for it not to be a problem. Never had it since in 1200 hours of Squirrel time.

Just a thought, if you're only 3 or 4 seconds away from hitting the trees if the controls lock, you're probably in the wrong place to start with.

I love the B2 for filming work - terrific performance - but it would be nice if Eurocopter upped the hydraulic power and maybe put another rubber band on the drive.

[nigelh]

Freewheel . so nice to hear that . So enlighten me ...what have you learned ??

Krobar. I dont think you will have experienced jack stall as it happens only when heavy and fast and high G. Eurocopter haters ( i hate the co but not the product !!) will bang on about it but i have thrown them around in a very heavy handed manner for years, often heavy and have never encountered it . I have also spoken to many other pilots with many more hours than me ....and none of them have either . I do not doubt that it can happen but i do doubt it can happen under normal flying , even wing overs etc:ok:
Personally if i thought i had just dinged a tree i would have a little look around before my next flight :rolleyes:

[ThomasTheTankEngine]

Did it happen as you describe, i.e. did the aircraft actually contact the trees, ground etc. Even if it didn't contact Id want eng involved before further flight, due to the controls locking up.

No brainer as far as I'm concerned, land shut down & get eng involved

[Ascend Charlie]

Thomas, it is a "normal" thing for AS350s to do. Happened to me when travelling at speed and did a climbing right turn - controls went rock-hard until I released all pressure and the speed bled off from the nose-high attitude.

On another occasion, similar situation, it didn't lock up, but it flicked left to the level attitude.

[spencer17]

@NigelH Same :ok:, I don't know what these guys are doing to the squirrel. Meantime I have more then 7,000 hours on type and did all kinds of work with it but never had a so called "Jack Stall". Once I had a hydraulic failure (the belt went) during a dive towards a loch for picking up water for fire fighting. The squirrel is absolutely flyable without hydraulic. Cut the hydraulic with the switch on the pitch (not the test button) tighten the grip and follow the book;). Nothing unexpected will happen, no ditching, no hitting trees.

Always happy landings
Specer17

[Freewheel]

NigelH

Same as you. I just couldn't formulate the words at the time without sounding like I was bagging the pilot or the aircraft, which at this early stage seems a bit unfair.

The book is vague, but gives food for thought when read before you get into it.

If, as a number of posters have found, it happens to you, prior reading of the book, thinking about the situation and acting accordingly should put you in a position that it's not too much of a drama. That's not to say you won't get caught out, none of us here can say we haven't, but it stacks the odds in your favour.

I hadn't contemplated Spencer's solution for Jack Stall, I would have thought the accumulator would return pressure for a short period in such a situation, given that the pump itself would still be running at the time of the Jack Stall. It strikes me as similar to shutting down the good engine after a failure in a multi, but that's just my theory.

And yes, a supplimentary walk around is a very good idea. There's somebody on the North Sea that is probably very thankful a supplimentary walk around was conducted, but nobody's mentioned that on the thread yet.....

[somepitch]

i have talked to a couple of pilots who have had jack stall happen in the mountains, both in very benign phases of flight (cruise and cruise descent respectively). they were not performing aggressive maneuvers or in any way abusing/throwing around the a/c. they both experienced stiffening of controls which went away after a few seconds, and were at sufficient altitude that it did not endanger the flight. their best guesses were that there were mountain wind currents that momentarily loaded the disc in some way that overpowered the servos.

i think to insinuate that all pilots that experience jack stall are in some way flying like cowboys (though surely SOME are) is going a little bit far. one of the aforementioned pilots had over 13000 hrs, with multiple thousands in a-stars, before he experienced it.

[nigelh]

Wait a minute :eek: i dont think spencer meant he would cut hydraulics off during jack stall !!!! Firstly it is only transient ( 1-3 secs) and secondly the manual tells you clearly what to do ...that is unload the system by reducing collective. If you think of it , the system is already working at full tilt but not coping so how do you think it would help by getting rid of that help ? ie turning off the hyds....... At the moment you get the jack stall you will be heading towards a steep right angle of bank and going fast ...i have done that before with hyds off and i can tell you you need to be a weight lifter to cope and bring it back level. I now fully understand why in the book it says keep speed below say 80kn and do shallow turns :ok: Just like it says dont hovver without them .....it can be done ...i have done it (badly) but again the book is right. They obviously dont just write it for fun.
Anyway i say if you want to do a high g pull at weight fine but i would either do it on a left turn or be sure i havent got high obstacles on my right. Just an idea ...and if you do get it ....yr ham fisted and i pity your girlfriend:=

somepitch just seen yr message. I agree that in mountains with large updrafts it may be possible without mishandling, but i would be getting the engineers to check the pump is working properly. i have done a fair bit in mountains in canada heliskiing 7 up plus 6 skiis and back packs in 40knots ....very bumpy but never a sign of this jack stall.

[SHortshaft]

This thread has an interesting focus. It was the machines fault!!

I wonder how many helicopter company managers are prepared to accept the argument that a control lock up, in conditions far away from those described in the flight manual for such an event, can be assigned to ‘jack stall’ and should not be the subject of further technical investigation; let alone that such an incident is an acceptable excuse for flying ‘through’ the trees.

To then attempt a further flight, unless the ‘local Taliban’ are after you, without stopping for a visual inspection and consultations with an engineer/mechanic simply beggars belief.

I only hope that we are not all muttering “there but for the grace of……!

[spencer17]

The servo accumulators should provide assistance for a few seconds, why not in the event of a "jack stall"?
I did not say that you guys experienced a "jack stall" fly like rodeo cowboys:=.
There are for sure do's and don't's for every aircraft and compared with others the squirrel (A-Star) is very forgiving.
I believe that it can happen but never experienced it myself .
Once a ran into real bad turbulence and probably high disc loads and rapid control movements overcharged the hydraulic system but control forces were only slightly higher then normal. Reducing torque and speed solved the problem. Maybe that was the beginning of a "jack stall", I don't know. But this happened on my worst flight ever. It scared the sh:mad: out of me and I'm not easy to scare.

Spencer17

[Arm out the window]

The accumulators only provide the same or less pressure than the normal hydraulic system, so they won't provide anything extra in the jack stall situation, which is when, as I understand it, flight loads exceed the capacity of the hydraulic jacks to oppose them.
If the aircraft had great big kick-arse hydraulic jacks and enough pressure to move them, jack stall wouldn't be a problem.

As it is, I've only felt it when trying to induce it on purpose for demonstrations - high speed, high power, pull reasonable g, feel feedback, reduce severity of manoeuvre and reduce collective, feedback goes away.

Depending on the condition of the particular hydraulic system and how the aircraft is being flown, plus gust loads perhaps, it seems it can happen in less severe flight regimes - close to the ground, not good as in this case.

The continuing flight after the tree strike thing doesn't sound that great, though.

[407 Driver]

Spencer17, you scare me. Ignoring the aircraft's limitations WILL NOT make them go away !

All others, especially Shortshaft, well posted.

I will not comment on the details of this incident.

Some of you have already read between the lines, and have a good idea what may have happened.

What I will say is simple. The HYD system is a known weakness of this aircraft, so never allow yourself in a position where you NEED to use it for control inputs.
Fly this type smoothly and professionally, and give yourself every available "Exit".

[Shawn Coyle]

Due to the contact with the trees, we got a report out of this incident.
How many others have had similar incidents and not reported them? Why didn't they report them? Did they write them up in the tech log? In the USA, send a NASA ASRS report, or use the HAI reporting system.
But for the sake of all the other AS350 drivers, report it!

[SASless]

Everyone calls the event "Jack Stall" but someone correct if I am wrong here....in "Jack Stall" one reduces collective to recover.....is this not the situation that occurred....the recovery action had already been taken well prior to onset of the controls locking.

On a fairly fast descent, in a turn, with low torque, the cyclic and collective locked up

Also...if the recovery action is to reduce collective....how does one do that if the controls are "locked" up?

Is it possible what happened here is the hydraulic pump cavitated due to the hydraulic fluid finding its way to the top of the tank and leaving the pickup open to air at the bottom of the tank? Thus, the real problem was a simple hydraulics failure that was cured by some positive "G" returning to the aircraft.

The Alouette III used to do that in severe turbulence in the mountains.....hit a very strong down draft and the controls would go stiff and pass a bit of feedback into the controls.....when the next up draft came along all was well again.

[[email protected]]

As Sasless says, Jackstall does not 'lock up' the controls, the aerodynamic backloads (particularly on the retreating side with the highest AoA) overcome the power of the servo jacks and force them to the bottom of their travel.

The resulting pitch up and roll right is identical to retreating blade stall.

Recovery is to reduce the severity of the manoeuvre, either by reducing collective pitch, relaxing back pressure on the cyclic or both, depending on the flight regime. If the controls were locked up, recovery would be impossible. Turning off the hydraulics will not help, even a little bit.

If the controls 'lock up' you have a different problem or you have misinterpreted what is happening.

As for wazzing and zooming with skiers on board - don't push it to the limits and don't think that giving them a bit of a thrill entitles you to exceed what you would do with your wife and kids on board.

[jellycopter]

Sasless

I like your theory but I don't think its correct in this case as the AS350 lets the pilot know of lost hyd pressure by flashing the warning light and activating the warning horn. Neither of these were present in the pilots report.

JJ

[dude12345]

Why does the as350 still have HYD pump belt drive???? Why not come off the transmission like most other types????? Do away with the s##ty little belts???

[JimEli]

>
...sending the aircraft into trees. Control was regained and the aircraft appeared to be okay. The group of skiers were dropped off and a subsequent flight attempted when a vertical vibration was noticed...
<

It appears the pilot made more than one error...

[ehstars]

Your words are a bit harsh for someone who wasn't there, don't you think? Well, take it from someone who was there and that has 4000 hours on the Astar, 9000 hours total time and 5 years of heli-ski experience, and yes, it does matter if you are a ski pilot because it is a different flying world when you are heli-skiing for example, you are never more than 3-4 seconds from tree's, on the way up, or, on the way down. I have had a hydraulic belt break once and had a hydraulic pump fail another time and both times the controls were control-able, and both those times there was time to press the collective hydraulic switch, but this time was different, this time it was like the helicopter was being pulled into the mountain beside me. As for hitting the tree's, I was unaware I had hit any trees as there was no indication that I had. I elected to take off again for a bit of a test flight, without passengers, to see if I could identify what was happening to the hydraulics, when just seconds after lift off I wasback on the ground because of a moderate vibration. TSB found 2 hydraulic servo's that failed the extension/retraction speed's, and, they came up with a theory why the hydraulics indeed locked up. One of the servo's drastically failed the test.

[[email protected]]

you are never more than 3-4 seconds from tree's, on the way up, or, on the way down

Why? what height agl are you flying?

One of the servo's drastically failed the test.

It clearly wasn't Jackstall or 'servo transparency' then.

[oldbeefer]

With a fleet of 30 350s that have around 300k hrs, have never had this problem - wonder if the servos were still in service when they shouldn't have been?

[nigelh]

He is right on heliski ops that you do spend a lot of time pretty close to trees when on the lower slopes ( below the alpine runs ). I have flown with a number of these canadian heliski pilots over the years in Whistler and Tiax and monashees and have never come across one less than AAA excellent . They are all truly superb pilots and perform impossible landings , toe in , one skid etc with 40 kn winds etc etc Respect !! He was there and did what he did and i can only imagine we would have all done the same . Flying out there IS different to what most of us experience and certain things are done which we wouldnt do ie sometimes you may have to get out and hot refuel yourself leaving controls unmanned ...there is no alternative . I never thought this was jack stall as i would only expect the cyclic to seize up and not the collective . I also believe it is a high G event and would not happen at low torque and lsing height .
At least it ended up happy !!

[Mark Six]

I know it's annoying when people who weren't there try to judge your actions or tell you what your should have done, so I won't do that. I'd be interested to hear (with the benefit of hindsight) whether you would do anything different if faced with the same situation again. Nigelh, not sure why you say "...i can only imagine we would have all done the same...", 'cos I can only imagine I would not have done the same. Also mystified why you don't think the collective would be equally affected if the cyclic "siezed up" due to a hydraulics/servo problem.

[Shawn Coyle]

There is an emergency procedure in the 350 FM called Main Servo Valve Seizure - it has no symptoms or indications as to what the pilot will see if there is such a seizure. It is interesting to note that the immediate action is to shut off the hydraulics...
There is also a very old (1990 era) service letter that talks about this in an oblique way - mentions different extend retract times for the servos. Worth looking at if you're an AS350 driver...

[nigelh]

Mark . IF the pilot had been aware of a blade strike OF COURSE he would have inspected the blades , but he was not aware of any strike . Under the circumstances of wat i thought was jack stall , i would boot the pax out and do a flight test starting with a hovver ...just as he did .
The manual says reduce collective to reduce the G force ....and funnily enough that is the way to do it !!!!

[IHL]

The AS 350 has a documented history of loss of control events.

I've attached an interesting TSB (Canada) report, as well as the appendix to the report which lists 25 loss of control events.


Aviation Investigation Report
Hydraulic Flight Control Malfunction
Vancouver Island Helicopters
Eurocopter AS 350 B2 (Helicopter) C-GNMJ
Kamarang, Guyana
06 February 2005



Transportation Safety Board of Canada - AVIATION REPORTS - 2005 - A05F0025 (http://www.tsb.gc.ca/eng/rapports-reports/aviation/2005/a05f0025/a05f0025.asp)


Loss of Control Occurences:
Transportation Safety Board of Canada - AVIATION REPORTS - 2005 - A05F0025 (http://www.tsb.gc.ca/eng/rapports-reports/aviation/2005/a05f0025/a05f0025_sec3.asp)

[[email protected]]

I think with a servo valve seizure (or suspected one due to control malfunction), the drill on every helicopter I have flown is to deselect the hyds - in an aircraft with 2 systems it is a question of deciding which system is at fault.

It would appear that there maybe more issues with the 350 servos than just 'transparency' since a sticking servo valve would produce the 'locked up' controls symptom.

[Shawn Coyle]

Oldbeefer
The failures on the AS350 series seems to be mostly with Dunlap servos, and in particular with servos that do not meet the tolerances for extend retract times. Hopefully your maintenance folks are on top of that sort of thing.

crab:
What other helicopters have a servo jam emergency in the FM? I don't recall seeing it anywhere else as a specific emergency in all the types I've flown.

[[email protected]]

Shawn, it might not say servo valve seizure but that is what control malfunctions (Sea King, Wessex, Lynx) mean - either a hardover or a seizure and the drill is to select the faulty system off.

[whatsarunway]

I had a chat to a eurocopter man recently about getting a dual hydraulic system on the b2 to counter this problem, and he said as you guys said that the weak part in the chain is the actuators and not the pump but the reason he gave for a poor performing actuator was if they had one that could handle greater loads the actuator would shatter the starflex, maybe i picked it up wrong but he seemed to be saying that the poor performing actuator was in effect letting you know with SCT that you had gone too far or the turbulance had brought you too far.


would be interested if anyone has another take on that. seeing as my ass is in an an Astar for 6 hours a day 6 days a week!

[Shawn Coyle]

whatsarunway:
If that were the case, there would be a lot of shattered starflex heads on AS 355s and EC-130s. They all have dual hydraulics, and there is a mod for the AS350B4 for dual hydraulics (if it isn't standard).

[nigelh]

Good point .

[widgeon]

I thought that dual hyd only gave redundancy ( if one channel fails the other takes over ) , it does not make the actuators more powerful. As at point of interest are there many cases of "transparancy" on the AS355.

[JimEli]

My information (as of 1/29/09), states the EC-130B4 dual hydraulic system is available as an option on a _new_ B3. Retrofitting an existing AS350 is not an approved modification, as it requires replacement of components of the flight controls, hub-shaft, MGB and includes reinforcing the tail boom.

[whatsarunway]

what i was saying was that the dual hydraulics eliminates the problem of hydraulic failures as a result of a belt or similar but it does not eliminate the problem of the weak actuator and the week actuator is so because if it were stronger it would shatter the starflex.

i have flown b2, b3,(not fitted as standard i know ) and ec130 all with dual hyd and was warned about SCT on them all.


its what i have been told, im not saying its true.

and also if the starflex is so good, why does the ec120 have such a different head although they call it a starflex from memory it has dampers and weights etc.
:confused:

[SHortshaft]

Why does the EC 120 have such a different head?

Perhaps it has something to do with the EC 120 not being a French helicopter. It was a JV between France, Singapore and China...and 10 to 15 years 'more modern' than the AS 350.

[widgeon]

I think the dynamic components were 100 pct france.
China built the fuselage and Im not sure what the other share was.

[mrneo]

One of this days i was type training a pilot and since he was for firefighting directly on the 350, we trainned some emergencies as far as close to real. the first time i saw a real HYD light was during that training sessions, after i chased the cause and looks like with low G or when one hard land and go up in the sky again is possible to have that red light. And maybe there´s some persons around that don´t pay the attention that they should pay to hidraulic acumulators, as i have seen in some type examinations.
Well to considerations, if one have servo transparency is because hyd power is no more capable of sustain the loads transmitted by the blades, decrease load factor on the rotor and almost immediatly everithing return to normal. Second one should not confuse jack stall with hyd failure due to low G ( happens that the system is like that and the hyd pump can suffer from oil starvation, conducting to a real hyd failure), if one have that situation and the power acumulators are in bad shape well is like having hyd failure. the hyd pressure takes a wile to return, wile enought to waste hyd acumulators if one does not stay cool. my advice is to study the situation when that happened, and published it here.
almost 1000 h on 350´s and never experienced jack stall , even to show to trainees.
good flights