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.