The Electras were destroyed by a single catastrophic coupling of two frequencies that converged, the propellor shaft wobble and turbulence flexing the wing. Even people who should know fail to see it has nothing to do with anything but converging frequencies. If there is a rotor bounce at a certain frequency and a wobble at the tail rotor gearbox nothing will happen if those frequencies remain discreet. Matched up, they destroy the helicopter simply because they are on the same frequency. Voodoo, witchcraft, whatever. It cannot possibly have anything to do with engineering.

How many of those you have knowledge of have thrown a blade inertia weight?

If talking about the lead weight bonded inside the blade spar, not aware of any 206 that had "thrown" an inertia weight. However, there were a couple 206 blade failures due to inertia weight bond voids that caused fatigue cracks in the spar and its subsequent failure in flight. These events were one of the examples I commented on earlier in the thread that the NYC 206 wasnt the 1st 206 to lose its MR drive and roof beam as a unit.

You're thinking what I'm thinking, just the weak link was not the gearbox case. That would explain the bend in the mast at the top of the case as the fulcrum and the folding of the tailboom.

A main rotor shaft under load has considerable amount of twist under normal conditions. It has been decades since I actually saw the twist when witnessing a calibration, but I think that it is in the 60-90 degree range. That is why a small amount of localized damage will lead to a total failure. Also, there is much discussion on the net about mast bumping which seems to focus on Robinson accidents, which does not apply to most Bell accidents. In a Bell product, the main rotor shaft contacts adjacent structure and causes the localized damage that cascades into total failure.

No, it has not.

His insinuation that the rotor head bumping the mast would cause the mast to deform 3 feet away from the fulcrum is a stretch of physics to say the least. I don’t know when the bend happened either but I’d be putting my money on impact with the ground/water if I was forced to place a bet.

ASN summarises the Kentucky accident with: "The wreckage distribution was consistent with an in-flight separation of the main rotor and tailboom... Both the main rotor assembly and tailboom separated in overload". It took something significant to cause that to happen.

There must be a point where mast deflection causes resultant off-centre rotor mass to cause even greater deflection of the mast and everything to spiral out of control until the whole system is torn from fuselage. With a detailed dynamic finite element model of rotor system, this could be simulated without killing anyone in the process.

The explanation proposed by The Sultan seems reasonable for New York accident. I wonder if the rotor tip that was missing as seen in the recovery footage has been located? I had read that the search for components had ended some days back.

FWIW: you'll find the Kentucky accident, along with a subsequent Canadian 206 accident, were both due to fatigue cracks in the blade spar. And both those accidents share distinct differences from the NYC accident even though it appears there is a similar failure mode. So it might be a bit premature to group them all together at this point.

Correction: I intermixed two separate Air Evac accidents in my recollection of events. The MR spar failure was in Indiana, not KY, and did not result in the loss of the roof beam, but did result in the mast shearing at the hub and the transmission departed at the lift links with the roof beam stayed with the aircraft. The Canadian 206 spar failure did lose the MR/roof beam. However, my comment there being distinct differences between the NYC 206 still stands.

Yeah, the significant thing that caused the Air Evac breakup was the guy probably ended up inverted or falling backwards. The thing broke up because the aircraft ended up way outside of its flight envelope.

The mast bending at the swashplate… do you really think you can drop a transmission and rotor system assembly from 500 feet and all of the damage to it must have happened before it slammed into the ground? The torque on the mast when the blades and transmission hit Mother Earth doing terminal velocity wouldn’t have an effect on any of the components that are designed for dynamic strength and not static strength? I think blades are gonna break, masts are gonna bend, pitch control rods are gonna snap, things in general are gonna get nasty. There was a chunk missing out of the Air Evac’s MRB but notice how it wasn’t attributed to being just a fact of life when your machine is breaking up.

I would suggest that the torque on hitting the water would be relatively low. As the rotor system descended there would be negligible torque with the forces being gravity and rotational speed from the blades rotating. On impact the only torque would be generated by water resistance.

and water is really quite hard when hit at speed.

What about looping back to the initial sequence with the sound that Blancolirio added to the video?

The ~ 1/rev noice must be a lead to something.

The videos of the rotor assy winding down show one blade shorter than the other.

If it did it start with a blade throwing the outer part it would explain most of the things, maybe even the bent rotor mast.

In the video there is another object visible for just a few frames as the tail departs, a little bit higher up. It's easy to miss without single stepping through the frames. It is there for only a few frames, then not seen again. I haven't noticed anyone commenting on it. I suppose it could be a puff of smoke, or perhaps it's the missing blade tip?

Could a sudden loss of anti-torque thrust caused by:

1. Tail rotor blade failure,
2. Tail rotor gearbox failure; or
3. Tail rotor drive shaft failure,

Have been the starting initiator for this whole failure sequence, as it appears on the videos?

Loss of anti torque would be from one of the above mentioned or similar.

But if the Blancolirio video is properly synced in audio, the initial happening is a 1/rev. sound.

The rotational speed of the yaw is very fast despite the forward airspeed. About the same as in hover in a sim when practicing the same thing.
I would expect the yaw to be much slower in Forward flight from a loss of anti torque thrust.

I would not expect the dynamic forces to rip the tail away in the yaw after having lost the tail rotor.
The tail rotor causes a opposite torque equal to the main rotor torque when working properly and that is caused by a single force in the dnd of the tail boom. For bending/breaking the tailboom, a aerodynamic widespread force probably causes less strain on the tail boom than a single force.


Back to the 1/rev. sound it might be related to:

- Throwing a part of the blade, causing a thremendous imbalance in the dynamic parts shaking the complete helicopter apart?

- Or, what? VH Blades shaking?

-Or, what?

SPLAT!
 

I was told that, because of surface tension, water is as hard as cement when impacted at speed.

Surface tension has nothing to do with it. It's just the incompressibility of the water, and its mass resisting any force trying to accelerate it to get it out of the way of the impacting object. The surface tension is a much weaker force by far.

I think the nodal beam system is quite robust, despite being tuned for the OEM blades. Assuming the maintenance schedules are adhered to, would VHA hopping ever be more than an uncomfortable experience?

But it's still very hard, regardless of the reason - ask SAR divers who try to jump as low and slow as possible.

Surely we have exhausted most reasonable causes and are now going in circles - it must be time now to wait for the NTSB to give the answers.

crab, I am not sure that they have found all of the pieces yet. There was some discussion about some of the tail trotor drive shaft sections not having been accounted for a few days back. (They may have been, of course, at this point).

As to how hard water is: yeah, our SAR swimmer deployment limits were 10 feet and 10 kts GS.

Flexible:
From the diagrams many posts up, the Tail Rotor system on the Long Ranger "pushes" in its anti torque function. (In comparison, the Seahawks/Blackhawks I flew had a "pull" tail rotor system).
Would the loss of tail drive not induce a right rotation of the nose rather than the left rotation seen in the video?
Further that thought, if the tail drive was lost as the initiating event, would that not reduce the load on the tail boom (the push is removed) and thus leave something else as the reason for the forward folding (seen on the video) of the tail boom? Some force caused that material failure.

If a tail rotor blade failed, though, or if a pitch link failed, that would set up a vibration that would manifest along the tail boom down to the attach point ... but wouldn't that be at a higher pitch/frequency than the 1 per rev vibration being discussed (as discerned from the audio?)

While discounting nothing, I don't think that the failures you listed would manifest themselves in what was seen on the video...something else seems to have been the initiating event / failure.

I did not find any discussions around the initial sounds, that was the initial events that we can distinguish.

If the Blancolirio YouTube video (posted earlier) is correct with sounds and timing, the helicopter was flying approx straight and level when these ~1/rev frequency pulsed noice arose.

If the sound matching is correct, I’m having a hard time seeing it is not a clear lead to the cause of the accident.

I assume it's absolutely ridiculous to suggest it might have hit a drone?

Not ridiculous at all. It’s one possibility of how to break a blade for example.
Also a place where the drone density could be expected to be above average.

What say we at least try to use some sort of factual evidence to base our wildest speculations upon.

This Thread is closed for a few days.

Hot off the press.

https://www.faasafety.gov/files/noti..._Vibration.pdf

If that is their primary area of concern it would seem to rule out a lot of other theories.

Surely pilots aren't repeatedly experiencing severe vertical bounce without reporting it?

The Airworthiness Concern Sheet shared by TwinHueyMan in #428 doesn't mention the New York accident, rather a 206L, N9984K, that landed safely in Washington state on 26 Sept 2024 despite substantial damage to the tailboom following continued (vertical) vibrations, see: https://asn.flightsafety.org/wikibase/454639. Still, is there a connection?

I have various comments on a few of the earlier posts:

Lonewolf_50 (#423): From the video you perceive a left yaw motion of the fuselage which you note would be contrary to a loss of tail rotor thrust. But several others perceive a right yaw of the fuselage which would then be consistent with a loss of tail rotor thrust. Watching the video it is hard to tell which direction the yaw actually is (see of example zoomed in clip from 16:39 onwards in the video linked at #391).

JamesT73J (#420): You ask wouldn't the VH hop ever be more than an "uncomfortable experience"? That isn't how some seem to describe it elsewhere on this thread and on the VH blades thread linked by Chock Puller at #361. It sounds scary in some cases.

hanche (#415): You mention an object seen briefly as the tail departs. If you look at the wreckage images in #363, it seems likely the rotors cut various parts of the tailboom so many smaller pieces were probably cut away. It would be very hard to work out which they are in the video, even the original version.

AAKEE (#414): Thanks for the image of your analysis of the audio from the break-up. The NTSB would surely be using that audio to try to help work out what occurred. When you refer to the "rotor assembly winding down" I assume you mean after it had already detached from the fuselage rather than earlier on? My post #340 has a screen shot that suggests one blade might be shorter than the other by that point but that could still be an illusion due to the pixelated image. Other screen shots I attempted didn't show such asymmetry in blade length. If that portion of the rotor departed in the air, it would still need to be determined whether that happened first or only after the rotor(s) struck the tail boom etc.

TwinHueyMan (#411): You feel there is a greater prospect of mast bending on ground impact than when the rotors detached from the helicopter(s). I can see either event could be violent enough to cause the damage that can be seen on the mast(s). To roughly compare one against the other, consider the kinetic energy stored in the rotor at cruise and the energy of a free falling rotor hitting the ground. I roughly estimate the 206L rotor might have 840 kJ of stored energy. If rotor strikes fuselage that can translate to a lot of force or moment exerted on the mast. If rotor is assumed to fall around 500ft (1437' msl - 900' msl) then pessimistically, and neglecting any autorotation or drag, it would hit the ground at around 57 m/s. Assuming the rotor system above the mast is around 140kg, then it collapsing onto the mask on impact would equate to around 230 kJ of energy release, so around 30% of the energy stored in the driven rotor when torn from the fuselage. I realise this is a crude comparison and the reality will all depend on how kinetic energy converts to damage to the components.

wrench1 (#410): You indicate fatigue cracks in blade spar of the Kentucky accident. But are you referring to the loss of the 206L-1 N114AE on 6 June 2013? The NTSB final report makes no reference to "fatigue" and I couldn't find fatigue mentioned in the airframe report of that accident either.

I don't think so for the same reason you mention, no reference to the NYC accident. Plus you wouldn’t see an ACS issued in that manner during the Prelim part of an investigation. But thats not to say there could be an ACS issued on the NYC one once it moves to the Factual part of the investigation.

No. I had corrected my post to reflect it was one in Indiana, N37AE in 2008. My bad.

​​​​​​​

Also hot off the press. Not much new info.

https://data.ntsb.gov/carol-repgen/a...ort/199991/pdf

Juan Brown has picked up the VHA angle:


Something I need a bit of education about. I understand the 2/rpm bounce from aerodynamic loads on a 2-bladed rotor, There's some reference to the accident aircraft exhibiting tail wag at ground idle. I'm a little confused about the dynamics here; there's no aerodynamic load, is this just balance of a rotating mass? How would composite blades exacerbate this, compared to the OEM aluminium honeycomb blades?

The tail wag on the ground is due to an RPM-dependent lateral imbalance caused by uneven fore-aft positioning of the blades, called Sweep. Incorrect sweep can be canceled out by lateral balance weights on the hub/in the blade pins, but they’re not effective until you are at 100% rpm (which is also what you balance the rotor for). Sweep can be tough to set properly when setting up a rotor head without the proper fixture, and I’ve met many a mechanic that doesn’t believe in adjusting sweep during rotor smoothing.

Van Horn has stated in their IL that incorrect sweep of the blades can exasperate the in-flight vertical hop occurrence rate/severity.

First, the ACS pertains to an incident from Sept 2024 and is not associated with the NYC accident. However, both the “collective bounce” mentioned in the ACS and the “tail wag” occur with Bell blades as well. Bell issued an OSN in the 70s on the “collective bounce” and Post 225 offers reasons for the tail wag, which is more an excessive 1 per at mast pole/MR hub connection. In severe cases you can also see its effects with the landing gear crosstube flexing in rhythm with the tailboom wag. Now whether the VH blades provide an easier path to those 2 conditions I don’t any recall references to that, other than both VH and Bell provided the same guidance steps to mitigate those events.

Bearing in mind that I have nearly 1,000 hours PIC fixed-wing time but about 5 in rotary-wing, i must say that, especially when right seat in a Bell 206 LR, I was amazed at the immense forces to which all drive components, especially the rotor blades, are subjected. Engine(s), gear boxes and drive trains, hubs, swashplates, weights and counterweights, control rods, and blades seem to be locked in mortal combat to see which component can shake its neighbors into catastrophic failure! Hats off to Igor Sikorsky and all who followed into the amazing piece of kit that is the helicopter. No wonder my fixed-wing flight instructor called choppers "Frantic Palm Trees"!

- Ed

From 0:50 into his video, Juan remarks that some people have given him feedback on a difference in altitude of the helicopter from before to after it is obscured by the building (being the Ellipse at Newport). There is a version of the video showing the (full) wide angle view without panning or zooming into the helicopter. So the helicopter trajectory is seen consistently, even if through a 'fish-eye' lens:
From that video, I have merged multiple screen shots. While the footage in the clip starts soon before the helicopter moves behind the building, it isn't clear to me there is any significant altitude change. So what have those people observed?

https://cimg0.ibsrv.net/gimg/pprune....1660090ad7.jpg

The preliminary NTSB report indicates altitude data changing from 625' to 675' msl soon before the break-up but the altitude data from ADS-B is possibly only given to a 25' resolution to start with:
https://cimg5.ibsrv.net/gimg/pprune....fa07c9dc64.jpg

Based on projecting from ground features, the 675' data point in the report would roughly align with the helicopter emerging from behind the building in the video.
There is another point in the NTSB preliminary report that still mystifies me: It says: "...Debris was also recovered... from a rooftop near the Hoboken, New Jersey, transit building". They don't indicate what debris that was though that would have been known. Was this debris significant? Based on the description, that location is around 500m from where the helicopter experienced its sudden yaw and subsequent breakup (location is obscured behind building at lower left in video screen shot above, see my red arrow). So either (1) it already parted the helicopter earlier in its flight, (2) it was thrown back through its initial momentum or (3) it was very light and drifted with the wind to that rooftop location, which is quite separate from where the major debris items landed in the river as seen below (the video camera position is approximately at location "C" with the Ellipse building circled in yellow):

https://cimg9.ibsrv.net/gimg/pprune....649f8c1fbf.jpg

There are a number of items missing from the tailboom assembly which may not be noticeable in the later footage? Considering it was mentioned and the aircraft appears to be in level flight and intact as it emerges from behind the building, I would guess that there is some significance to the debris.

The proposed bill to ban tours and all other non-essential NYC helicopter traffic is gathering pace. I just can't see the rich folk driving out to their Hampton estates on a Friday evening. I suspect their political influence will stump this one.

https://nypost.com/2025/05/26/us-new...-federal-bill/

Part of the NY Post article has: "Supporters of a tourist-chopper ban argue that the tragic incident last month wasn’t an isolated incident, with at least 38 fatalities tied to helicopter crashes in New York City since 1977, according to The Associated Press".

Even if all of these are counted, it amounts to an average of 0.8 fatalities per year over that 48-year span! I wonder what it reduces to if only fatalities due to scenic tours (or other "non-essential" helicopter flights) are counted? Also, how many 3rd parties were killed as a result of the relevant accidents over all these years?

I wonder how that compares to annual motor vehicle accident fatalities in the New York area? Time to stop all non-essential motor vehicle movements in the NY area???

If there are legitimate safety concerns with how the tour operations are conducted, then by all means address any such issues!

This is the usual "bubble wrap me for life" crowd chiming in.
You'll notice that they don't cite how many people got into a helicopter, took their tour, and then got out. That would be in the millions, possibly tens of millions, over the course of almost 50 years.