Orange line should be from up right to down left

skadi

Not if the boom had swung round to the starboard side...

I agree that in a typical tail boom strike it would be the other direction but I believe I've marked the damage correctly and the face of the damage appears consistent with the direction of the main rotor.
It looks like it would have already detached or possibly twisted/rotated to make such damage possible and to be in-plane with the rotor disc.

I agree!
Now I have looked on a bigger screen and I`m with you that the bladestrike was not the primary cause of this accident as many here suggested first.

skadi

There is also this interesting PPRuNE thread on Van Horn blades from 2022.

I've bolded what could also be a similarity to this accident, 3 small children and the pilot's radio call for a refuel.

I think the blades may have hit the tailboom twice after it departed especially when you line up the parts as shown in the pic. Takes a lot of energy to slice the stabilizer at the winglet like that. The inboard break looks more like impact damage.
https://cimg5.ibsrv.net/gimg/pprune....74319b223b.jpg

Looks like some operators are taking some precautions... We received this email last week -->"We have a couple sets of lightly used 206L Van Horn blades on consignment P/N 20633000-101.

The prices are negotiable.

S/N A0XX Time since new: 1083.2 Time remaining: 14916.8 Asking price: $49,954

S/N A0XX Time since new: 1083.2 Time remaining: 14916.8 Asking price: $49,954

S/N A2XX Time since new: 100.6 Time remaining: 15899.4 Asking price: $66,750

S/N A2XX Time since new: 100.6 Time remaining: 15899.4 Asking price: $66,750"

https://demerarawaves.com/2022/12/07...pper-grounded/

As an aside, is there any particular advantage to the composite blades? What do they gain a 206 operator - are they more durable, easier to set (I know that's not the right word), or something else?

Cost. Bell blades have a 4000hr retirement. The Van Horn blade itself has a 16,000hr retirement with the metal grip plates replaced every 4000hrs.

Bell has also had a lot of issues in their blade shop in the last several years, rumor has it not many 206 blades make it past QC and out the door. Supply has dried up on OEM blades with Bell often giving “guesses” on when a blade order will be delivered (as alluded to earlier in this post). Some question if the 206B blades are even still being made, and the 206L blades have a priority to the 505 line.

Van Horn has blades in stock usually, plus they give you a bump in cruise speed, snappier handling, arguably more lift, and lower DOCs. Before the truth behind the bounce came to light it was all but a no-brainer.

I have also wondered about the damage seen at the tail boom fracture. In steady level cruising flight with the main rotor turning anti-clockwise (viewed from above) the tail rotor needs to provide an anti-clockwise anti-torque moment to the fuselage hence a tail rotor thrust directed to the right. The vertical stabilizer, with an apparent 5.5 degree incidence angle* to the fuselage centreline also provides an anti-torque side-force when in cruising flight. See following sketch:
https://cimg0.ibsrv.net/gimg/pprune....7bf567c059.png

With those forces on the tail, the left side of the tail boom will generally be in tension while right side will be in compression. Add in some tail boom vibrations or a sudden yaw and the compression on the right might increase further. Buckling only occurs due to compressive loads, so it seems logical that typically buckling might first occur on the right side. With a tail boom significantly weakened due to buckling, the right side could simply fracture in tensile overload. Where would that occur? Through a line of drill holes to accommodate the rivets attaching a frame to the inside of the boom (as is the case here). Those holes create stress-raisers and so it is the weakest place on the skin to resist tension. If the aircraft has accumulated many hours and load cycles, it is possible some of these holes already had fatigue cracking as well, but not significant enough to have been observed. Still, the talk earlier in the thread that this helicopter had a more noticeable recent tail waggle on the ground is a worrying sign.

If the tail folded to the right of the rest of the fuselage, that is the opposite of what I originally perceived from the video, but eyes and brain can play tricks and viewing the video linked by Gordy at #250 once again, I can now also see that possibility (fuselage yawing to the right or clockwise viewed from above per #250). The inertia of the tail boom relative to the fuselage would then amplify the compressive and tensile loads I mentioned above.

* Incidentally, the horizontal stabiliser 'end-plates' (or 'finlets' as referred to by NTSB) are apparently angles at 5 degrees in the opposite direction of the vertical stabiliser. That can be seen in the above graphic. This 'quirk' has been the subject of earlier discussion in a PPRuNe thread about the Bell 206 series.

Looking at the slowed down video, right before the aircraft yaws right, there seems to be a separation/ deflection of the tail boom itself- moving to the left. If the whole aircraft was yawing to the right as folks have observed, it adds up as a loss of tail (Loss of anti-torque). But if the tail cone itself moves left as the video suggests (my eyes anyway) but in a way to separate from the fuselage, that implies something else. It says that the anti-torque function of the tail rotor was in a right yaw. This may seem counter-intuitive, but looking through literature, the section of the tail control tube would be 'pulling' for a right yaw, 'pushing' for left yaw. If I interpret this correctly then a tail boom separation or folding in either direction would change the effective length of the control points, stretching that tube. This would be a tail control "Hardover", with right yaw action pushing the tail cone left, and in such case complete the separation of the tail cone. Note also that the same pushrod fracture location is coincident to the tail cone break. A pinch point, under tension, would cause a control tube to break at the pinch location. Like a stick on your knee. From there, my guess is we have a main blade strike, both blades, on the folded tail. I don't believe the slowed rotor had enough energy for both blades to break like the photos show from a water impact while not under power. If they hit the tail, under power, however, both can crack, as well as having the incredibly high torque needed to rip the gearbox and airframe structure. If the rumor of visual tail shaking observed is confirmed, that can support a tail cone first theory. If it were a blade strike first- why would the tail first swing to the left? at that airspeed, tail thrust would not be much, but would be biased to the right..Unless the blade strike inertia folded the tail, but it appears the empennage is not turning until the tail cone goes left.
The investigators will look shear, wear, fretting, fatigue, to narrow the search- but these guys are pros (I recognize some from the videos, having worked with them). They have for certain already noticed areas of clean break versus tearing breaks. They will see the dark areas that are a sign of fretting if any is there.

As already pointed out VHA Blades can cause excessive Tail Wag on the ground when at Ground Idle (206L).

It's disconcerting to see it let alone feel it.

The first time I experienced it before any information was issued was "how have we effed up for this to happen".

A point to maybe consider during certain ops such as sight seeing work is the amount of time spent at GI inbetween flights whilst loading/unloading pax, refueling etc with the tail boom wagging about.

VHA advice is not to sweep the blades for lateral balance as this can introduce the Tail Wag, but to use Hub Chord weights. This is a minor mod to do in accordance with a Bell issued TB, however it's not a standard set up without conforming with the TB to modify the Hub to accept chord balance weights.

Another VHA statement was released that in order to reduce the onset of vertical hop is to sweep both blades aft two points.

Somewhat contradictory?

VHA blades are an accountants dream and reports from the pilots are that they do notice slight performance issues at altitude. No FMS supplement issued though.

From a maintenance perspective I'm reserving judgement as something doesn't sit quite right.

Whether related to this tradegy I cannot and would form an opinion without further data.

Maybe we should resurrect the original thread on VHA MR Blades?

Given it seems hard enough to clearly establish if the main fuselage yaws to right or left (with general consensus being a right or clockwise yaw?), I think it is even harder to establish from the video what the tail boom is doing and whether that occurs before, after or at same time as what is happening to the body. My current 'guess' is that one point in the breakup may have looked something like this (rotor facing aft is mostly omitted from sketch & gap in tailboom is simply due to graphic limitations of my drawing package):

https://cimg1.ibsrv.net/gimg/pprune....8e9fa74e1f.png
The damage to the left side finlet and lack of apparent damage to the right finlet suggests main rotor only struck tail boom items once tail boom was already breaking away as others have been observing.

Tail Rotor
 

We have not seen any photos of the tail rotor and vertical fin - or have I missed them.
Were they VHA blades too?

Thanks, that makes sense to me.

it is interesting to see aircraft plaftorm upscaling being applied to save design and certification cost, in a helicopter, its always the tail that seem to show design weakness first.

take the AS350, from the B to the B3, power went from 650hp to 1000hp, MTOW from 4300Lb to 6700Lb (EC130). All they did is add reinforcement plate at the root (fastening to the fuselage) of the tail, but nothing diferent in between.

Did the original designer provide such a generous cushion for safety that we have eroded little by little via upscaling?.

VHA Tail Rotor Blades are excellent and have an FMS supplement for altitude performance.

I believe Bell no longer manufacture Tail Rotor OEM blades as VHA have done a better job.

Credit where it's due.

I'm retired from flying for some time and I last flew the 206B and 206L quite a few years prior to the availability of the VHA MR blades. And I'm in no way suggesting that the VHA MR blades were the cause.

What is the current process for ensuring that 206 pilots are aware of the differences in performance and handling of the VHA MR bladed aircraft and that 206L pilots are aware of the recovery procedure from collective bounce?

I'm thinking of scenarios where a pilot starts working for a different operator, or a pilot's operator decides to switch blades due to availability/economics. Is there any potential for a pilot to remain unaware of just how different the blade behaviour can be in the 206L?

And regarding the letter of 17th March from VHA regarding collective bounce - is it correct to assume that this is just a refresh of previously documented information?

The Van Horn Blade thread can be found using this Link.

https://www.pprune.org/rotorheads/65...A+Rotor+Blades