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AS332L2 Ditching off Shetland: 23rd August 2013

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AS332L2 Ditching off Shetland: 23rd August 2013

Old 5th Nov 2013, 20:27
  #2081 (permalink)  
 
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What's this then:

The helicopter manufacturer was provided with a copy
of the recorded flight data for analysis. They concluded
from their analysis that, in the last 30 minutes of flight
prior to impact with the sea, the helicopter had behaved
as expected based on the recorded control inputs, and no
pre-impact malfunction was evident.
This initial analysis also showed that the combination of
the nose-high attitude, low airspeed, high rate of descent
and high power placed the helicopter in a vortex -ring state entry condition (VRS) during the final stages of the flight. The manufacturer’s modelling indicated that, in this condition, the reduced helicopter performance,
together with the limited height available, meant that the
impact with the sea was unavoidable
AAIB Special Bulletin: S7/2013
G-WNSB
EW/C2013/08/03
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Old 5th Nov 2013, 20:55
  #2082 (permalink)  
 
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Firstly it's the manufacturer's opinion, secondly it says "vortex ring state entry conditions", which is not the same as vortex ring state or even IVRS, and thirdly it was a final consequence of all that preceded. It would be a bit like proclaiming that the helicopter crashed because it hit the sea - true, but a rather pointless conclusion.
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Old 5th Nov 2013, 21:37
  #2083 (permalink)  
 
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the reduced helicopter performance,
What reduced the performance of the aircraft?

What changed with the aircraft that resulted in a loss of performance of the aircraft?
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Old 5th Nov 2013, 22:03
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TC:

John Dixson has a great post in one of the V-22 threads about actual entry into VRS.

Have you seen it?

If you look at the altitude where this aircraft was before things went pear shaped ...
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Old 6th Nov 2013, 00:32
  #2085 (permalink)  
 
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I am not sure this is about VRS. Once airspeed is below 30 kts, with a high rate of descent, there was simply not enough power to overcome the inertia before the sea got in the way. VRS takes time to develop. This is low speed, height ROD condition. Similar to descending downwind.

As HC says, the actual mechanism is just to result of the initial problem. Failure to maintain airspeed whilst descending.

DB
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Old 6th Nov 2013, 12:57
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Semantics guys: Wake up and stop splitting hairs will you!

This cab departed its intended flight path because the pilot(s) allowed it to - FACT.
When a helicopter experiences a:
combination of
the nose-high attitude, low airspeed, high rate of descent
and high power placed the helicopter in a vortex -ring state entry condition (VRS)
.....trust me implicitly when I tell you this, but it is in IVRS - FACT.

Aircraft rarely crash as a consequence of departing their intended flight path, but without a suitable height for recovery, they will always crash when in IVRS or VRS.


When the IVRS became established and it DID become established in this report [placed the helicopter in a vortex -ring state entry condition (VRS) ]
The pilot was committed to impact the sea.

Stop fiddling around the edges the lot of you. IF you have ANY understanding in the field of helicopter aerodynamics, you will see this for what it is. Plain and simple.

* I know dozens of pages have been written about cockpit warnings/autopilot playing up/repeater lights, etc. but the final report will leave absolutely no doubt whatsoever about how this accident cam to be.
The CVR and graph telemetry will see to that.

Double Bogey: You really worry me....................................
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Old 6th Nov 2013, 13:43
  #2087 (permalink)  
 
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TC.....what is it about VRS that bothers you so much?

Several Test Pilots have told us here that modern Helicopters have the power to fly out of VRS even if it is well developed.

You know very well that it matters not which direction you fly out of the descending column of air.....be it rearwards even....you can recover the aircraft.

This accident has as far more to do with a loss of control by the Crew than VRS.

Remember one of the key elements in VRS.....a very high Collective Setting.....which was not the case here.....the Collective was set way too low as you recall.

The EC folks are looking for a way out of this by pointing a finger at anything that might focus folks on anything but the EC design and engineering.

This is very likely a clear case of Crew Failure to maintain Airspeed and all this blatter about VRS is simply background noise.
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Old 6th Nov 2013, 13:55
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TC

There's no hair-splitting going on. People are quite within their rights to debate whether IVRS was the cause of the crash or simply a 'state' the aircraft ended up in after a sequence of events that went badly wrong.

It's like saying the Costa Concordia sank because it struck rocks. Well, yes it did but it would never have occured had other holes in the cheese not lined up.

To say the crash was caused by IVRS or VRS is a gross over-simplification of a somewhat complex scenario.
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Old 6th Nov 2013, 13:55
  #2089 (permalink)  
 
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TC, with warmest regards ....

I spent a few years flying helicopters off the back end of ships, sometimes in the dark. One of the well known traps of approaching the ship at night, when it was moonless and cloudy, pattern altitude at 400' or a bit lower if the ceiling was coming down ... and you are flying in from about a mile and a half, was that "hole" or that "sudden sinking feeling" that came at somewhere between half a mile and an eighth of a mile, depending on ship speed and wind velocity and direction, and how well you were on profile.

As you slowed down to reduce your closure rate, you'd lose translational lift. If you weren't staying a bit ahead of the aircraft, or were fixating on the line up or on one instrument, or something distracted you ... as you slowed down you could begin to drop toward the ocean, particularly if you were a few knots fast and had reduced collective and raised the nose a bit to adjust closure/speed. More than once I hollared for power from the PNF seat (and more than once I pulled up on the collective while hollaring, better to sort it out later ... ) often in duet with the crewman. I had it hollared at me a few times as well.

That "falling into the black hole" had nothing to do with vortex ring state.

It had to do with lift loss at low altitude due to decel, reducing power, and losing the benefit of translational lift at a time when outside references didn't quickly cue you to the aircraft beginning to settle.

The mishap aircraft in this case was low altitude, crap weather, few to visual cues of settling ... I don't know, I am guessing but I suspect poor. If the crew were mostly letting Otto fly, or HAL, or whomever, and Otto was the one leading the decel (or a decel sooner/faster that should have been ... ) the reaction time to "Hey, we are falling arse first into the black hole" and correcting with power and pitch would be a bit delayed compared to if they were flying manually.
VRS?
Not necessary to fall arse first into the hole left by a lack of lift at that transition zone.
If you delay the reaction, you get a RoD which you may not arrest with that armpit of collective a few seconds later. Momentum and all that.

While I confess to you that the above includes some guesswork, that regime of flight need not get into VRS in order to end up falling down and arse first when one did not intend to.
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Old 6th Nov 2013, 14:39
  #2090 (permalink)  
 
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Maybe this is why the Canadians call VRS and Settling with power 2 completely different things. Could it have actually been settling with power? Just not enough power to arrest the rate of descent once it was noticed?

VRS is used to often IMHO. Its an easy out. Ever tried to get a helicopter into the incipient VRS state? Its not that easy, but everyone seems to blame it for a lot of accidents when 'SWP' would better fit.
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Old 6th Nov 2013, 15:07
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Helimutt.......absolutely correct. Two very different situations.
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Old 6th Nov 2013, 15:44
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Originally Posted by Lonewolf_50
... Momentum and all that. ...

Our friend has a point.

Newton 1 & 2.
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Old 6th Nov 2013, 18:47
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Oh dear..........

SAS/Helimut/Lonewolf:

You scare me. I am stunned that seemingly experienced aviators such as yourselves should come out with such comments.
Where to begin.
SAS I suppose as you seem to be the most experienced of them all, so let's pick 'em off with the biggest first theory:
May I respectfully advertise my credentials in this arena:
I teach IVRS/VRS/SWP/PS for a living. Currently I have with me, our Canadian colleagues who are over here to learn all about this and various other 'sinister malfunctions/aerodynamic phenomena.
In the late 80's I was a defence witness for the New York crash of a Sea King which entered IVRS and crashed in one of the urban parks near the display line. The pilot was an ex student of mine from the RCAF, Shearwater.NS.
I was a naval aviator and instructor in the good old FAA and taught ship ops then and teach it weekly now to 5 different nations across the globe. We fly all types of ship approaches including SE profiles and IVRS scenarios - one of them being approaches to ships at night.

You're an american yes? American helo pilots are probably the most confused when it comes to IVRS and SWP. In fact nearly every US rotary aviator who has NOT done some form of training in europe has never heard of VRS. They think everything orientates around SWP/PS. It is only when they cross pol, that they discover there is another phenomena.
For helinuts sake let me make something very clear:
IVRS/VRS is an aerodynamic phenomena. It is to do with airflow and main rotors (pedantically it also affects TR's but this is not for this arena). It is to do with big green arrows/dirty airflow/stalling/roots/tips etc.
SWP is a performance phenomena which is purely and simply to do with engine output Vs weight and trajectory of the aircraft. The two phenomena are NOT compatible.
Example: A rotorcraft that descends into disturbed air whilst decelerating below a certain speed and with a set pitch will experience aerodynamic disturbances which diverge.
A rotorcraft which arrives at a determined point in space (a landing site or the back of a ship) whilst in the descent and at a speed where to arrest that speed requires "X" amount of power and finds that the engines cannot provide that amount of power - will thus fail to arrest said aircraft in time. Much like racing up to the red traffic light too quickly and the brakes on your perfectly serviceable car are not capable of arresting the weight of that car at that speed, in time: SWP.

Americans just don't get it.
Some Europeans just don't get it.

OK, onto the real McCoy (IVRS/VRS).

Today I was speaking to my senior Instructor about this very phenomenon. He was quizzical about the difference between IVRS and VRS. In fact he somewhat doubted it.
An hour later a good friend of mine came in who was from my "era" and we had the same conversation. This common conversation was about the Puma crash you are all talking about here. I pointed out the conclusion made by the AAIB.
He concurred and stated it was unequivical what had happend...it was "approaching VRS state"...which we term: IVRS (Incipient).

Do you know why there was a discrepancy between my senior Instructor and the other pilot? Age. One was in his 40's and the other nearly 60.
The latter had not only learned from a young age about IVRS/VRS but he had also flown both states
When we went thru training in the mil and also in our early stages of Instructing, we both taught these phenomena (IVRS/VRS) and differentiated betweeh the two. Now, both flight regimes are banned flight profiles and no-one talks about them much anymore (The same can be said for hydraulic lock during "Jack Stall" and for many: Double Engine Failure demos.) They aren't practiced therefore they aren't mainline conversation - there are no "experts" in this area anymore except those nearing retirement.
So - let's bring this to a close, I've harped on to the disbelievers for far too long:

When a rotorcraft is in a RoD (usually but not always <300'/min) whilst experiencing a low airspeed (usually but not always 20-30kts), the rotorcraft will develop a gentle runaway in RoD unless the pilot arrests the situation early. Often even though the pilot may notice these two parameters (ht and spd) he or she may attempt to arrest it by applying pitch to the main rotors. Often this works and the a/c returns to 'normal'. However the situation gets worse and the RoD deepens. At early onset VRS this will manifest itself by an increase in airframe vibration and a slugging of control response in cyclic and collective only. The a/c will yaw but it can be easily controlled in this plane. At this degree of onset the rotorcraft is relatively responsive and recoverable within tens of feet . If the situation is delayed for just a few more seconds, feedback of the controls becomes much less effective and often hundreds of feet is required to recover (3-500').
IF the situation continues further then fully developed VRS is experienced upon which the pilot becomes a passenger. The cyclic and or the collective will have NO EFFECT (SASless this means you can't move backwards even!). The pilot will not be capable of recovering from the fully developed state unless and until the nose dips sufficiently (of its own accord) for the airspeed to recover allowing the aircraft to be controlled in some shape or form. Most helicopters are neutrally stable and tend to return to this state eventually of their own accord, but not always. The height loss experienced during fully developed VRS can easily be in the region of thousands of feet, which is why we used to teach/demo VRS at entry height NB 12000 feet and all the crew had to wear parachutes

Very very few rotary aviators TODAY either understand IVRS/VRS/SWP nor have they experienced it for real.

Believe me the crew of this Puma entered IVRS and suffered the bows and arrows of such a consequence.
This is why the AAIB made no bones about it or anything else and chose their words very carefully. Accept it - move on. Everything else is confetti.

Last edited by Thomas coupling; 6th Nov 2013 at 19:03.
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Old 6th Nov 2013, 19:15
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Originally Posted by Thomas coupling
In fact nearly every US rotary aviator who has NOT done some form of training in europe has never heard of VRS.
Where do you come up with this bombast?
I learned the difference in flight school, circa 1981-82, in Milton, Florida, Training Wing 5, HT-8 and HT-18.

I again recommend to you the posts John Dixon made about VRS in the V-22 thread. Very good stuff.

I don't rule out the possibility of the mishap helicopter experiencing the problem of incipient VRS in this mishap ... you'd understand this if you had bothered to read my post for comprehension.
What I noted is that VRS isn't the only explanation.
Delayed reaction can do something similar, which is why it is so important to teach and know the difference. Also why it is so important to fly your aircraft, and to stay ahead of it, particularly in transitions ...
Americans just don't get it.
You are wrong about that.
Stow the bombast and stick to how things fly.
PS: Nick Lappos gets it, and IIRC he's American.

Last edited by Lonewolf_50; 6th Nov 2013 at 19:39.
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Old 6th Nov 2013, 20:01
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Americans just don't get it.
Some Europeans just don't get it.
Really? Do go ahead and fully explain just why that is will you?
Is there something about your being British that gives you that particular unique ability and insight into other's cognitive abilities?

Do you realize how effectively you just shot your own foot with such comments?

Get that chip off yer shoulder Mate and stick to the issues will you?

Several of us have taken issue with your view VRS is the final and most immediate cause of the crash. We see it much differently.

We do so based upon the information we gleaned from the AAIB Reports and our own experience, training, and education.

There is nothing unique to the British system, the Royal Navy, or your background that would provide you such a lofty perch to make such comments in any way more credible than any of us that differ with you.

Do keep your eye on the Ball please.
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Old 6th Nov 2013, 20:08
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SASless,

which part of:

"...combination of
the nose-high attitude, low airspeed, high rate of descent
and high power placed the helicopter in a vortex -ring state entry condition (VRS) ..."

don't you understand you rigid old bugger.

What you are falling back on/legitimising/ mitigating, can be taken to the nnnnth degree and you could say that the immediate cause of death was lack of oxygen to the body due to the inability to breath FFS

Are you contesting the AAIB now with all your 12000 posts???? Take a holiday.
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Old 6th Nov 2013, 20:13
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Are you contesting the AAIB now with all your 12000 posts???? Take a holiday.

I did TC.....in the UK where I sat across from Nick Lappos when he received the Barnes Wallis Award at the GAPAN Banquet.




To refresh some memories of what has been discussed before......


http://www.pprune.org/rotorheads/279...g-alt-vsi.html


TC.....until the AAIB issues a final report and definitively states exactly what they "think" caused the crash.....and it turns out to be VRS in their professional opinion......any categorical statement to that effect is premature.

Do tell us why you think IVRS would cause the Crash would you?

"Incipient" must mean something completely different in your English than it does in mine.


Lone,

The Army did a study in 1971 that was incorporated into Navy Training and has some effect upon the VRS limitations that apply to the Osprey yet today.....meaning the 20kts/800FPM ROD numbers.


TC,

You might chew on the information in this link a bit and see how it squares with your thoughts.



Vortex Ring State

Last edited by SASless; 6th Nov 2013 at 20:50.
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Old 6th Nov 2013, 21:55
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So, the final AAIB report is published. Its very short, here is the text:

Investigation into the accident to AS332L2 G-WNSB on 23rd August 2013

Cause: The aircraft crashed because it hit the sea, as a result of incipient vortex ring state.

Safety recommendation: Pilots should undergo increased training in the recognition of, and recovery from, vortex ring state

So now we know, and with a bit of extra sim time doing VRS training we will all be safe and it won't happen again. Phew, we can now go back to business as usual.
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Old 6th Nov 2013, 22:44
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vrs??

I haven't followed the whole thread, I do not know what the ROD was in the final stages of the accident, but this might shed some light as to whether it was IVRS or VRS or not (as I suspect)!

VORTEX RING STATE






To calculate downwash speed (reference for VRS for a particular Helicopter) take disc loading in LBS/Sq.ft × 210, then take the square root of answer, this will give you speed in ft/sec. (100% downwash speed)


To be conservative, if you now take 50% of this you will avoid VRS.


At 50% you may feel some conditions of IVRS, at 75% you will be in IVRS.


Example for S76.
Formula: Disc Loading (Lbs/sq/ft) × 210 = Χ. √ Χ = ft/sec.


S76 Disc area: (π×r×r) r =22ft
3.14×22×22 = 1520²ft.


Disc Loading = AUW = 11700 = 7.70Lbs/sq/ft.
DISC AREA 1520


7.70 × 210 = 1617. √1617= 40.2ft/sec.


40.2ft/sec = 24kts = 2412ft/min Downwash speed.


50% of 2412 =1206 ft/min.


S76 @

11700 Lbs Downwash speed = 2412ft min. 50% = 1206ft/min.
11000 Lbs Downwash speed = 2339ft/min. 50% = 1170ft/min
10500 Lbs Downwash speed = 2286ft/min. 50% = 1143ft/min
10000 Lbs Downwash speed = 2232ft/min. 50% = 1116ft/min
9500 Lbs Downwash speed = 2173ft/min. 50% = 1086ft/min
9000 Lbs Downwash speed = 2116ft/min. 50% = 1058ft/min


Goodnight.
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Old 6th Nov 2013, 23:00
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As I view Page 5 of the latest AAIB Report....the aircraft seemed to pitch down sharply 2-3 seconds after the Collective Pitch was increased 8.5 seconds before impact with the Sea. You reckon that might have had something to do with the ROD increase?
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