Another Robinson crash

[Aussierob]

1 dead, 1 injured after helicopter crashes in dense Vancouver Island bush - British Columbia - CBC News (http://www.cbc.ca/news/canada/british-columbia/vancouver-island-helicopter-crash-1.4317454)

[206Fan]

UPDATE: One person dies in helicopter crash northwest of the Campbell River Airport - Comox Valley Record (http://www.comoxvalleyrecord.com/local-news/breaking-helicopter-crash-north-east-of-the-campbell-river-airport/)

[twinstar_ca]

The pilot killed was a very well respected member of the canadian helicopter industry. She will be sorely missed and condolences to all her friends and family. I personally did not know her but I have several friends grieving... :( :(

[pilot1234567]

The pilot killed was a very well respected member of the canadian helicopter industry. She will be sorely missed and condolences to all her friends and family. I personally did not know her but I have several friends grieving... :( :(

Would you mind PMing me her name? I'm just hoping it's not who I think it is.

[malabo]

Name hasn’t been released yet, previously worked at STARS in Grand Prairie and Highland.

Not sure why this thread needs to be titled as “another” by some Robinson-bashing cretin. Lots of 44’s flying with a reputation in the industry (outside of pprune) as good helicopters.

[lowfat]

Probably because Since 1982, there have been at least 512 deaths in 291 Robinson crashes worldwide..

Does seem a touch high. figures shamelessly googled.

Safer than riding a Motorbike I guess

Condolences to all concerned

[helicopter-redeye]

3305 Bell UH1 variants were destroyed during the Vietnam war (figures shamelessly Googled). Does seem a touch high.

As Disraeli put it. Lies. Damn lies.... And statistics.

[aa777888]

In the US, currently a similar number of Bells and Robinsons are crashing each year. Of course, there are more of each than any other type, so that skews the stat's. And, no doubt the Bells are doing more challenging stuff like long line work, and Robinsons are doing more challenging stuff like primary instruction. And, with the operating costs so low, no doubt the Robinsons are being flown by people with a lot less experience (myself included), which also skews the stat's.

Given that this latest event may involve someone with a lot of experience, perhaps it is the exception rather than the rule. Nevertheless, with all of the design improvements since the original 22's and 44's were launched, and SFAR 73, it's getting awfully hard to blame the machine itself as the root of all evil nowadays. That said, there are still a lot of people with a bad taste in their mouth from an earlier time in the evolution of the Robinson designs, some who have personally lost someone dear to them, and we'll hear from them loudly whenever a Robinson goes down, regardless of the cause.

Regardless of whether you think Robinsons are "death machines" or not, there is no question they have made rotary wing flight available and accessible to many more people than would otherwise be the case, and I personally know many Robinson pilots who happily fly a Robinson rather than not fly at all.

[krypton_john]

The thing is, when evaluating the merits of the machine, is to eliminate the pilots from the equation.

IOW how many crashes caused by the design/manufacture and not the pilot or maintenance?

There is a suggestion that some RH blades have failed catastrophically in flight when operated in accordance with best practice (no low g, no high speed into turbulence etc). If there are a number of those then we have a problem.

[Helisweet]

We will compare with new basic trainers:


https://aviation-safety.net/wikibase/dblist.php?AcType=G2CA

[mickjoebill]

One occupant survived the crash and was extracted from wreckage, so presumably there was no fire.

It is so unfortunate that the improved crash worthiness version of the fuel system took as long as it did to be implemented.

Mjb

[heliduck]

The number of crashes per hours flown expressed as a percentage of the total hours flown by each manufacturers fleet would be an interesting comparison, but I’m shamelessly too lazy to google it.

[[email protected]]

Helisweet - the interesting statistic from all those Guimbal accidents was zero fatalities, I assume that was your point of comparison to the Robinsons.

[Bell_ringer]

There are also a few that are students losing the tail while near the ground, probably struggling with the fenestron.

[Winnie]

The name is out now.

Karen Coulter.

I never met her, but tough loss regardless.

RIP

[PANews]

I would expect there to be more incidents with Robinson's than most other manufacture simply because of the numbers.

Slagging off Robinson for killing and burning many might be an acceptable issue if there was a similar thread highlighting the killing capabilities of the AS350/H125 series [and quite a few other legacy types].

The manufacturer of the AS350 spent a great deal of time and trouble enhancing the safety of their 40 years old design - so much so that the added safety was [is] effectively delivering the passengers to a funeral pyre. The timescale of those improvements is such that many crews that would have died in many an accident are, thanks to stroking seats and other improvements, now being killed by post-crash fire.

Putting right what may be the last detail - the creation of a crashworthy fuel tank - has taken 40 years. Far longer than Robinson has been an issue.

It may be that this 'final solution' for the AS350 will simply highlight another legacy killer in the design. For that we need to wait.

[[email protected]]

The difference is about what is causing the crash - in the Robinsons there is still a higher proportion of mid-air breakups than any other make.

Which other make has such a history of rotor separation, MR to tail boom strikes and in-flight breakup?

If you are dead before you hit the ground then crashworthiness becomes irrelevant.

[Hughes500]

Crab
I m no Robinson fan but the Super Puma must be neck and neck with the Robinson

[DIBO]

not following this thread, but as I just read the article in this link, I might as well post it here:
Robinson crash injures four at the Namur aerodrome in Temploux (Belgium) - Aviation24.be (http://www.aviation24.be/miscellaneous/accidents/helicopter-crash-injures-4-namur-aerodrome-temploux-belgium/)

[[email protected]]

Hughes500 - I know what you mean but it is the number of crashes to produce the high level of fatalities that is the poor Robinson stat - the Super Puma manages to achieve a high body count with far fewer accidents.

[aa777888]

Copied nearly verbatim from my post on this in another thread back in July 2017...

For all you Robinson bashers, a quick search of the NTSB database shows that, for 2017 through the end of July (the last time I looked at the stat's), the following breakdown of accidents by manufacturer occurred:

Sikorsky - 2 (11 fatalities total)
Schweizer - 3
All other types - 6 (2 fatalities total)
Hughes/MD - 8 (6 fatalities total)
Airbus/Eurocopter - 9 (1 fatality total)
Bell - 25 (20 fatalities total)
Robinson - 34 (17 fatalities total)

Bell seems to be holding its own with Robinson in the accident and fatality departments, at least in the US (can't speak to worldwide). I did this sort of quick study for 2016 and Bells actually had more accidents and fatalities than Robinsons in the US. And yet they are one of the most respected makes. Should we not be flying Bell helicopters, either? Of course not.

I'm unable to find any data showing hours flown by each make, but it's easy to suspect that both Robinson and Bell are the busiest. Given that Robinsons do the bulk of the training in the US, that's a lot of hours doing high risk stuff. Similarly, it's easy to visualize that Bells are doing the bulk of other types of high risk work (long line, etc.) Busy + risky = more opportunity for accidents.

If anyone had any rate based (hour normalized) statistics for the US, by make, for a recent year (modern Robinsons with modern training, and all the latest AD's and SB's complied with, and definitely not pre-SFAR 73), I'd be very interested to see them.

[Bell_ringer]

Copied nearly verbatim from my post on this in another thread back in July 2017...

For all you Robinson bashers, a quick search of the NTSB database shows that, for 2017 through the end of July (the last time I looked at the stat's), the following breakdown of accidents by manufacturer occurred:

Sikorsky - 2 (11 fatalities total)
Schweizer - 3
All other types - 6 (2 fatalities total)
Hughes/MD - 8 (6 fatalities total)
Airbus/Eurocopter - 9 (1 fatality total)
Bell - 25 (20 fatalities total)
Robinson - 34 (17 fatalities total)


Let's unpack this a bit.
Both Bell and Robinson had 11 Fatal accidents totalling 27 fatalities for Bell and 20 for Robbie up until 1 October.
These are global stats.

Now the Bell's have higher seating capacity with 1 accident taking 9 lives in a 412, as an example. This does skew the "facts" a little.
What is more relevant are that the Bell accidents are generally commercial in nature including rescue services and photography, a number of these are CFIT.

The Robbie accidents are more recreational or light commercial work. The majority are described as impacting terrain in VMC. The impact being a result of an unplanned/unexpected loss of altitude.

CFIT accidents you'd expect during high risk ops. Falling out the sky for no apparent reason during relatively mundane ops is something wholly different.

Robinson would always have you believe it's pilot error, that just seems a bit of a cop out. You can sing the praises of that little tin-can deathtrap but the reality is that it continues to cull pilots and and often good-ones at that.

[[email protected]]

Bell ringer - :ok::ok::ok: it is ALL about context, simple numbers don't give the true picture as you have shown.

[aa777888]

What is more relevant are that the Bell accidents are generally commercial in nature including rescue services and photography, a number of these are CFIT.

The Robbie accidents are more recreational or light commercial work. The majority are described as impacting terrain in VMC. The impact being a result of an unplanned/unexpected loss of altitude.
Bell_ringer: where can I read about the details of each one of these incidents to that I can come to these same conclusions? Is there a single database that I can enter into for this information?

[gulliBell]

Bell_ringer unpacked it pretty good. The B412 prang mentioned I think was in Indonesia, pilot flew into a mountain in bad weather. A completely different scenario to Robinson helicopters falling out of 8/8ths of blue sky. I'm not sure what sort of conclusions @aa777888 might come to from closer examination of accident data, or the purpose in doing this. From my perspective, I'm perfectly happy to fly a B206, B212, B412 or any other Bell helicopter. No way would you get me in any flavour of Robinson helicopter.

[gator2]

I fly a 44 because its all I can afford. I've been in some awfully rough air, and just slowed down. I have, however, been pretty damn scared a couple of times when a passenger has bumped the cyclic, trying to take a picture, or get to their cell phone or whatever. If I'd had a little looser grip on the pole I think I'd be dead. I wonder how many of the inexplicable smooth clear air disintegrations are due to that?

[gulliBell]

Given the dual controls in Robinson helicopters are so easy to remove, why not remove them when flying said cyclic bumping passengers?

[gator2]

They are always removed when I fly. Passengers still bump the cyclic. They also drop their damn cell phones on the emergency beacon switch.


But the question is, do people think cyclic bumping may be leading to mast bumping?

[homonculus]

Bellringer has added a useful synopsis to this ongoing debate, but I would need to see the raw data and his analytical methodology before agreeing or disagreeing

All that matters is the number of fatal accidents - the number of deaths is due to aircraft capacity and multiple other factors, but a fatal accident is an accident with an impact speed that can kill

I am not sure I care if I die in a commercial or a 'light commercial' accident. I am still dead. The important issue is was it pilot error or aircraft malfunction.

So how many fatal accidents were clearly NOT pilot error? That is all that matters, for that determines the safety or otherwise of the aircraft, not the pilot

I feel safer in a turbine, and safer still in a twin, but I cant afford more than a Robbie for much of my flying. I sit on the fence - there does seem to be an issue with mast bumping BUT is it due to failure to slow down...... in other words if I am a careful driver am I more at risk in a Robbie?

I dont think we have the evidence one way or the other

[CRAN]

Gator,

Yes, I strongly suspect that many of the mast bumping incidents in Robinson are related to the cyclic being knocked out of the pilots hands by a passenger knocking the centre post.

It's only happened to me once, by a friends wife sat beside me trying to point a scenery... we were in the mountains on a beautiful sunny evening, so you can imagine how the accident report would have read...

Despite the common doctrine for a two finger grip for fine control movements these days the cyclic gets a somewhat firmer grip from me.

CRAN

[aa777888]

At some point in the risk/reward spectrum things start to get a little silly. Hell, why leave the ground at all?

For me it's fly what I can (barely) afford, or not fly. For most people that choice is going to come down on the side of flying.

I will be the first to agree that pistons are not as reliable as turbines, that 3 blades are better than 2, that high inertia is better than low inertia, and that bladder tanks are better than no bladder tanks. And I agree that the list of Robinson AD's and SB's tells a story. But that story is now well evolved, and other than the recent uptick in apparent, overly fast, turbulence penetrations in lightly loaded R66's, modern stat's don't seem to say that there is a dramatic problem with flying these machines if they are flown within their specified limits to any greater extent than other machines.

That said, I'd still really like to take a look at the raw data the Bell_ringer alludes to, if someone can point me at it. The FAA data I see does not cause me to draw conclusions that Robinsons "simply fall out of the sky" at any greater rate than other makes, i.e. other makes "simply fall out of the sky" as well.

[gator2]

Cran: yep. I was in the snake river canyon with a guy who did it three times trying to take pictures. After the second time, I decided if he did it again I'd give him a ride. He didn't do it the fourth.


As you point out, the accident report would have said "loss of control due to turbulence in mountainous area".


I think there is a psychological tic at work here. We believe we can avoid CFIT, wires, clouds, and survive EOL. Just like when a guy dies of lung cancer, we all think "whew, he was a smoker, I'm not, I'll be ok"


But nobody thinks they can survive the 44 falling out of the sky for no reason. So that puts a whole different light on flying one of the things.


I think as long as you slow down in bad turbulence, they fall out of the sky because somebody bumps the damn center post. Its a lot more vulnerable than a joystick. And I feel better about flying them through that bit of psychological trickery.

[FlimsyFan]

The SFAR and associated SB and ADs have raised awareness for sure.

I’ve got to say, I hate flying our R66 one-up and low fuel. I dropped some pax the other month and headed off 15mins each way for fuel. It was a hot day, a bit thermally and I found myself pulling about 35% and flying at 90kts. I’ve spoken to blokes pulling max continuous one-up and being near VNE, but I just don’t think it’s good airmanship in that machine.

Like some others on here, RHC has allowed a cost effective introduction to rotary flight, and especially so into turbines. I love the machine and think it’s real capable. But the mast bumping issue isn’t a myth, so why take any chances?

Think I’m gonna duct tape my passengers’ arms to their sides from now on!

FF

[[email protected]]

If a machine has a Vne then you should be able to operate it (with due allowance for the Density Altitude on the day using the RFM) up to that figure, without having to take special care or avoid light turbulence in case it falls apart.

If the helo is unsafe at those speeds then the certification was wrong and the Vne and Vno should be revised downwards accordingly.

Of course that doesn't make Robinsons as competitive or attractive as the opposition so doubtless much pressure was exerted on the FAA to accommodate the certification - perhaps like SAC and the S-92's very remote likelihood of oil loss from the MRGB.

[FlimsyFan]

If a machine has a Vne then you should be able to operate it (with due allowance for the Density Altitude on the day using the RFM) up to that figure, without having to take special care or avoid light turbulence in case it falls apart.

If the helo is unsafe at those speeds then the certification was wrong and the Vne and Vno should be revised downwards accordingly.

Of course that doesn't make Robinsons as competitive or attractive as the opposition so doubtless much pressure was exerted on the FAA to accommodate the certification - perhaps like SAC and the S-92's very remote likelihood of oil loss from the MRGB.

Yellow arc now added to ASI with mandatory reduction in VNE in turbulent conditions, but I take your point.

I hope to be in something more substantial before long, but I will steadfastly refrain from badmouthing the Robbies.

I think when first certified the inherently more pronounced risk of mast bumping in the lighter and more powerful R66 was not necessarily a known quantity.

[Bell_ringer]

I hope to be in something more substantial before long, but I will steadfastly refrain from badmouthing the Robbies.


While I am occasionally a bit trite about the Robinsons, I endeavour to be constructive.
Ultimately what you find yourself flying is not within your control and a matter of circumstance, so the debate is largely academic.
Just remain aware, and ahead, of the foibles of whichever machine you find yourself in.

[vaqueroaero]

I have a couple of thousand hours in the R22 and maybe 700 in the R44. Recently I have found myself becoming very uncomfortable flying either of them. Not sure why.
I feel they don't help themselves by putting blade fixes on Youtube. I simply have no idea how any corporate lawyer approved that and then the latest VNE restriction placard doesn't really do anything other than give Robinson an out in a lawsuit."Oh, it must have been too windy and the pilot exceeded VNE. Prove otherwise. Thanks."
Mickey mouse fixes and nothing else.

[CappyJax]

The accident rate doesnt scare me in the Robbies, it is the specific examples of high time Robbie pilots having inflight break-ups that scares the crap out of me. It is always blamed on the pilot, but when a design feature causes a great deal of pilot error, then it is the designs fault and not the pilots fault. Look at the Guimbal and compare accident rates to the Robbies. The difference for the same role is astounding.

[[email protected]]

I think when first certified the inherently more pronounced risk of mast bumping in the lighter and more powerful R66 was not necessarily a known quantity. why the hell not? It makes a laughing stock of the certification process which is supposed to ensure the aircraft is airworthy.

[aa777888]

Look at the Guimbal and compare accident rates to the Robbies. The difference for the same role is astounding.
Where can that data be found for inspection? I'm interested in looking at it.

[9Aplus]

http://www.pprune.org/rotorheads/600303-another-robinson-crash.html#post9916145
or here
HeliHub.com Guimbal (http://helihub.com/tag/Guimbal+Accidents/)

[aa777888]

http://www.pprune.org/rotorheads/600303-another-robinson-crash.html#post9916145
or here
HeliHub.com Guimbal (http://helihub.com/tag/Guimbal+Accidents/)
There is no rate based data at either of those links. They are just lists of incidents.

[[email protected]]

But by reading the list of incidents and particularly their causes and number of fatalities you can get a pretty good idea of the risks associated with some machines.

[aa777888]

But by reading the list of incidents and particularly their causes and number of fatalities you can get a pretty good idea of the risks associated with some machines.
And I've done that with the FAA data. At least in the US, for the past two years, my observations (which may differ from others, since nearly 100% of that data is not final or complete), do not show that Robinsons are any more or less likely to "just fall out of the sky" any more regularly than Bells. There aren't enough incidents with other helicopter types for see any good trends. But every type of helicopter out there has had incidents due to "random" or "inexplicable" circumstances. I can't speak to worldwide data because I haven't studied it, and I've found it more difficult to compile.

Of those Robinsons which "just fell out of the sky", there is a clear trend associated with lightly loaded machines flown near Vne in turbulent conditions. I can't speak for those pilots, but I've been cautioned by my instructors since day one to be very mindful of that combination of conditions.

Now by no means am I a Robinson "apologist". It is what it is: a very lightweight, piston powered, two-bladed, low inertia machine, the 66 being an exception only with regard to its engine. That makes it inherently less capable in many respects, and with smaller safety margins. And I've flown the G2--auto's were ridiculously easy compared to the 22 or 44, so I can appreciate this. Nevertheless, as long as you enter into that realm with your eyes open, it becomes a risk/reward issue, which, at its core, is an exercise in economics. For most people this assumption of risk equates to learn or don't learn (or join the military and hope you make the cut). Or, after that, fly or don't fly, either for work as the prototypical CFI, or for business or pleasure. Because any other machine is going to cost nearly twice as much to operate. In the US, dual in an R22 is $250-300, the rare Cabri is $450'ish, the same as dual in an R44. For owners, the same thing, as even the least expensive turbine, including the R66, is going to be at least twice the operating cost of an R44, and probably more.

At any rate, for a demographic that seemingly accepts insane risks in the ground environment (e.g. epic tales of working, and playing, in godforsaken places, motorcycles adventures, etc.), it's interesting that at its level of affordability, the risk/reward ratio of the Robinsons aren't actually applauded. Safer than riding those motorcycles, anyway!

[Paul Cantrell]

But by reading the list of incidents and particularly their causes and number of fatalities you can get a pretty good idea of the risks associated with some machines.

Crab, it's pretty hard to disagree with that statement, but I'll try! :E

Seriously, I really don't disagree that you can come to some conclusions by looking at the accident data, but there are a lot of factors to think about. People have always pointed out that one of the reasons Robinson helicopters crash so much is because they're flown by so many inexperienced pilots. So, when a low time pilot bumps the mast is that a failure of the pilot or of the machine? As you yourself said:

why the hell not? It makes a laughing stock of the certification process which is supposed to ensure the aircraft is airworthy.

So, why are we allowing new aircraft (R66, Bell 505) to continue to be certified with teetering systems?

And I've done that with the FAA data.

I did a similar search, looking at fatal accidents that occurred in cruise flight. Not unsurprisingly, a lot of them are iIMC/weather and CFIT types of accidents. People have been drilling that into us for years (and yet we still keep doing it). But as aa777888 says, all the teetering systems are represented: Bell, Robison, Hiller. It's actually a bit chilling how many of them there are. So, should the FAA still be certifying teetering systems? I must admit I was a little disappointed when Bell used the L4 rotor system for the 505. I was hoping for a mini-407 rotor system for that aircraft. Maybe you just can't get a machine with 4 blades to compete price wise with a 2 bladed machine like the R66.

I fly a 44 because its all I can afford. I've been in some awfully rough air, and just slowed down. I have, however, been pretty damn scared a couple of times when a passenger has bumped the cyclic, trying to take a picture, or get to their cell phone or whatever. If I'd had a little looser grip on the pole I think I'd be dead. I wonder how many of the inexplicable smooth clear air disintegrations are due to that?

It's an interesting question. For the first 10 years I taught, we were required to teach low gee pushovers (by my school, and then later by the FAA in SFAR 73). It takes a pretty good cyclic push or some pretty turbulent air to start getting right rolls. When I've been flying in 30G45 I'll get some gentle right rolls and it's pretty obvious to anyone trained in teetering systems that it's time to slow down in those conditions. As for the push, if someone shoves your cyclic by mistake, yeah, it's a concern, but as long as it doesn't pop out of your hand I think it's unlikely that you'll go low gee - your reaction to put the cyclic back where it was is probably fast enough to avoid mast bumping (unless, I dunno, they manage to make it go full deflection?). In any case, I think that holding the cyclic with your fist rather than two fingers in cruise is probably not a terrible idea.

Like most people, I'm not in love with the Robinson T-bar cyclic. Most people don't know, but the first 2-3 R22s had narrower cockpits. I've got lots of time in the #2 R22 (the FAA crashed #1) and the cockpit was so narrow that it was difficult to do hovering autos from the left seat - trying to get your wrist around the throttle enough so that you'd be able to roll it all the way off, your hand/wrist would hit the door. They widened the cockpit a bit on the production aircraft (so, when Frank was designing the T-Bar, there was even less room than there is today).

The R44 and R66 don't have that excuse; there's plenty of room for a conventional cyclic and this would reduce a couple kinds of problems:

The first is what was mentioned above - the fact that the push-pull tube for the cyclic is mounted on the aircraft centerline, and that even with the left hand cyclic grip removed there is a small stub sticking out to the left, it's quite easy for a passenger to inadvertently hit the cyclic in flight. Photographers and females with handbags always arouse my suspicion :eek:

The other problem is that if an instructor is guarding the cyclic from the left seat while the student pilot is flying from the right, the instructor's cyclic grip is something like 6-12 inches in the air (because of the way the cyclic teeters on the central control rod). When the student moves the cyclic, they can move it in pitch and roll, but they can also move it in "teeter" which means the CFI has a 3 dimensional problem of trying to keep his hand near the cyclic grip... if the student does a quick move including moving his hand up or down it can be difficult for the CFI to retain control of the cyclic. It's not an huge problem for the CFI, but it does make it more difficult. I would be totally happy if Robinson installed conventional cyclic controls in the R44 and R66.

The recent caution range for the Robinson airspeed indicator is an interesting development. The amount of cyclic push you need to get below 0.5 gees is directly related to your speed... At 120 knots a pretty gentle push will get you light in your seat... At 60 knots it takes a pretty aggressive push. We could change the R22/44/66 Vne to 60 knots when a non-rated pilot is at the controls... That would put you in Schweitzer/Bell-47 territory for speed, but arguably there's no reason for a student pilot to be going all that fast. It might also provide an incentive for Robinson to change their head design to one less influenced by low gee...

[Bell_ringer]

So, why are we allowing new aircraft (R66, Bell 505) to continue to be certified with teetering systems?


These days, how many unexplained in-flight breakups do we see on teetering aircraft other than Robinson?
The issue may not be the architecture but rather the Robbie implementation thereof, including their coning hinge.

[Paul Cantrell]

These days, how many unexplained in-flight breakups do we see on teetering aircraft other than Robinson?
The issue may not be the architecture but rather the Robbie implementation thereof, including their coning hinge.

Like aa777888, my search was finding all manufacturers of teetering systems showing up in the fatal accidents. My guess is that if you correct for the experience of the pilots, the Bells are experiencing a similar failure rate.

Interestingly https://www.faa.gov/regulations_policies/rulemaking/recently_published/media/Final_Robinson.pdf

seems to support this. The teetering R22 and R44 saw accident rates lower than those of the Enstrom 280 and Schweizer 269 (but that's all accidents, not just fatal and not just mast bumping).

Comparing Bell and Hiller to Robinson, they show the Bell and Hiller substantially (25%) less accidents, but again this is not just fatals and not just mast bumping. Given that a large focus of SFAR 73 was mast bumping, I'm a little disappointed that they didn't break that specific form of accident out separately. Also interestingly, I saw at least one Bell mast bump / rotor separation where the cause was "inadvertent IMC" because iIMC caused the pilot to lose control and then bump the mast. You can't even depend on the summaries, you have to read the accident to be sure.

As for the Robinson Tri-Hinge rotor head... I'm not aware that it's ever been shown to have been a cause where a Bell style teetering head would have not. It was extensively studied during the SFAR 73 investigation, so in many ways it may be the most researched head in the industry. Still, I must admit that I worry that there may be some corner of the envelope, similar to the V-tail Bonanza, where that head design might do something unexpected. However, I have nothing to back up that fear.

In conclusion, the teetering head design has a large scary part of the envelope that some unlucky pilot enters on a semi-regular basis and pays the ultimate price for having done so. While all aircraft have restrictions on parts of their envelopes, this seems one that takes a large enough toll that we should question why we continue to allow it to be used?

[Bell_ringer]

Trying to make sense of light aircraft accidents and statistics is a black art, assuming you get a definitive conclusion notwithstanding the large differences in accident investigation globally. There will be little conclusive information until we see light aircraft with lightweight, affordable and crash-resistant cockpit recorders

The technology today wrt CFD analysis and modelling is far better than when Robinson looked at it the ages ago.
If I recall correctly, when Bell had issues with the 407 tail rotor excessively flapping they couldn't reproduce the issue either but yet the pedal stop was introduced and the issue ceased.

I am certain the Robinson phenomenon is a culmination of factors from design through operation.
It is after all a machine that is popular due to it's cost-effectiveness and cost comes with compromise. I suspect the machine could be improved quite significantly with an articulated head (ala Cabri) and conventional control systems but then that would cost a lot of cash making them somewhat less attractive.

[krypton_john]

Interesting presentation of rotor head design differences in teetering heads here:

Editorial: Too many NZ pilots dying in Robinson helicopters - NZ Herald (http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=11828571)

[blakmax]

I have in the past posted on adhesive bond failure issues with RHC blades. I suggest a review of those postings would aid discussions about past incidents. I stress that these issues related to earlier dash number blades. The latest blade versions have addressed my concerns and I give RHC credit for taking advice.

My point is that statistics alone are not an adequate guide to ongoing risks unless the efforts and timing of the manufacturer to address issues are taken into consideration.

So really, the issue I ask is what is the dash number of the blades involved in this crash? There may also be any number of other causes, but at least this one should be eliminated.

Regards

Blakmax

[aa777888]

Reading the NZ article, I was struck by what I thought was a rather larger number of R44 accidents worldwide than I would have thought possible: 95 worldwide with 58 fatalities since Jan '15.

Looking back into the FAA database for the period of Jan '15 to Apr '17 (when the article was published), I found 45 of those listed in the US. That probably makes sense, given that the bulk of Robinson operations can be logically assumed to be in the US. However I also found only 3 fatals in the US (5 total souls) out of those 45 US accidents. The article did not specify if that was 58 total fatal accidents worldwide, or 58 fatalities. Either way, the result is that the fatality rate, under either statistic, is much, much higher outside of the US. Indeed, with over 99% of all Robinson R44 fatalities being outside the US in that time period, combined with what almost certainly has to be a far lower operational tempo than in the US, it is no wonder that those outside of the US have a much lower opinion of Robinson helicopters.

This begs the question of what the heck is going on outside of the US with respect to Robinson maintenance, training and flight operations to cause this dramatic disparity in US vs. non-US Robinson accident and fatality rates. And one wonders does this disparity extend to other types as well?

While I was looking at the FAA database, I also took another look at the numbers for the period Jan '15 to Apr '17, to match up with the article time period:

Robinsons of all types: 79 total accidents of which 6 were fatals
Bells of all types: 80 total accidents of which 11 were fatals

My (subjective) breakdown of Robinson fatals is: 2 pilot errors, 1 maint. error, 1 IIMC, 2 undetermined ("fell out of the sky")

My (subjective) breakdown of the Bell fatals is: 1 pilot error, 1 maint. error, 3 IIMC, 1 CFIT, 2 mechanical failures, 3 undetermined ("fell out of the sky")

Strikingly similar. I wish I had data that gave the total flight hours for Robinsons and Bells over that same time period. It obviously makes a difference depending on whether or not the total hours flown by each type were comparable or not.

[Hot and Hi]

AA: Interesting analysis.
combined with what almost certainly has to be a far lower operational tempo than in the US
Excuse me for asking: What do you mean by "operational tempo"?

[aa777888]

AA: Interesting analysis.

Excuse me for asking: What do you mean by "operational tempo"?
Number of flight hours in a given type per day. There are lots of Robinson Hobbs meters ticking over in the US every day, not as many in other countries.

[Bell_ringer]

Number of flight hours in a given type per day. There are lots of Robinson Hobbs meters ticking over in the US every day, not as many in other countries.

Please substantiate this claim.
According to RHC recent announcements about 2016 sales stats 60% of their helicopters are shipped outside of the US.

[helicopter-redeye]

The USA is less than 40% of the total World.

[vaqueroaero]

This begs the question of what the heck is going on outside of the US with respect to Robinson maintenance, training and flight operations to cause this dramatic disparity in US vs. non-US Robinson accident and fatality rates.

The US has SFAR 73?

[aa777888]

Please substantiate this claim.
According to RHC recent announcements about 2016 sales stats 60% of their helicopters are shipped outside of the US.
I'm totally OK with being 100% wrong about that claim, Bell_ringer. Even if it is true that 60% or even 70% of total Robinson fleet hours per year occur outside the US, that still doesn't account for the vast differential in fatal events between the US and the rest of the world: in 27 months ending 1 Apr 2017, 3 fatal events (5 total deaths) in the US, vs. 58 worldwide (events or deaths, not sure, article did not specify).

Let's say it's 58 deaths, because the media will always go for the bigger, scarier number when digging up stat's and there are more deaths than accidents. Let's further assume the US only accounts for 30% of the relevant fleet hours. If you normalize the US contribution of deaths to 100% of the fleet hours, the US is contributing deaths at a rate of less than 1/3 that of the rest of the world.

SFAR 73 could be part of the reason why.

[Bell_ringer]

Let's say it's 58 deaths, because the media will always go for the bigger, scarier number when digging up stat's and there are more deaths than accidents. Let's further assume the US only accounts for 30% of the relevant fleet hours. If you normalize the US contribution of deaths to 100% of the fleet hours, the US is contributing deaths at a rate of less than 1/3 that of the rest of the world.


I'm not sure where you are getting your data.
NTSB database shows 6 US fatal accidents for 26 foreign (19%/81%).
You have to also take into account RHC popular markets like the Aus and Africa where mustering and game work is popular and high risk.
Number of incidents on their own is meaningless unless you can correlate the data to the number of departures, hours flown, type of operation amongst others.
The conclusion you are trying to draw lacks substance imho.

incidentally the US, back in 2015, supposedly accounted for 35% of the global civil fleet (all types).

[Bell_ringer]

I did some analysis from the NTSB database for the date range chose by AA above. It does make some interesting reading. Unfortunately the NTSB don't classify foreign accidents by operation which they do for US aircraft so it is not possible to validate the differences between them.

If you compare RHC to Bell (understanding they make different tools for different jobs) what you find is the following:
121 accidents (incl fatal) and incidents for RHC globally to 117 for Bell.
Of these 26% were fatal for RHC and 28% for Bell, fairly close.

65% of RHC accidents and incidents were US-based but the US only had 19% of fatal accidents.
68% of Bell accidents were US with 36% of the fatal accidents - which aligns to the % of the civil market the US has.

Interesting stuff but if you can't correlate this with the utilisation of the fleet no conclusions can be drawn.

What is more meaningful is how the US accidents are distributed across the various operations and how RHC compares to Bell in this regard.

For RHC 89% of accidents are related to part 91 GA with 100% of the fatalities.
1% are part 135 commercial ops and 9% part 137 agricultural.

Of Bell accidents 43% are part 91 GA (50% of the fatalities) , 11% part 135 (17% of the fatalities), 34% agricultural (25% of the fatalities) and 3% external load (no deaths).

This goes back to my previous assertion of Robinson ops and Bell's being used in higher risk environments.
While there is no specific data to back it up, I'm willing to bet a cold one that like for like Bell's are clocking more hours and given the relative numbers is a far safer platform than the Robbie.
But then most of us knew that already.

EDIT: There are definitely accidents missing from the foreign reports.
For the fatal Robbie foreign accidents quoted above Russia is the main culprit with 28%, Australia + NZ combined with 24% and Brazil with 16%.

[gulliBell]

I'm not sure how many Bell helicopters breakup in flight with an experienced pilot/instructor at the controls. Probably zero would be my guess. The same can't be said for Robinson helicopters.

[aa777888]

I did some analysis from the NTSB database for the date range chose by AA above. It does make some interesting reading.
Thanks for going through that exercise, Bell_ringer, most appreciated.

My take on it is it's just trading one set of risks for another.

Robinson risks: instructional environments, low time pilots, lower capability machine with smaller safety margins.

Bell risks: more likely to be found working at more complex tasks.

And, your point about comparing Part 91, the majority of Robinson op's, to the same for Bell, is a very good one. I did that for the same time period as before (1 Jan 2015 to 1 Apr 17), and the results were:

Robinson: 70 accidents of which 6 involved fatalities
Bell: 34 accidents of which 6 involved fatalities

It's interesting that the ratio of fatalities to accidents remains approx. 2:1 with the Bell's higher, whether it be all operations or limited to only Part 91 op's.

As for the beer bet ;-), if we restrict the hours to US civil (not military) hours only, I'll take that bet. I'd be willing to bet that Robinson hours actually exceed Bell hours in US civilian operations. At least in my neck of the woods Robinsons buzz around like honey bees all day long, but you rarely see a turbine helicopter of any type. And, according to the FAA civil aircraft registry, there are almost 3.5 times as many Robinsons as Bells registered: 2846 Robinsons of all types vs. 828 Bells of all types. Given the popularity in the US of Robinson helicopters for instruction, personal and light commercial use. could it be that the Bell fleet is working 3.5 times harder than the Robinson fleet?

But...without any actual data on hours flown by helicopter types, it is admittedly difficult to come to a definitive conclusion. Nevertheless, when restricted to the US, all other data tends to suggests that the two fleets are roughly comparable, although the large number of Robinson aircraft registrations tends to tilt things a little in Robinson's favor.

[aa777888]

I'm not sure how many Bell helicopters breakup in flight with an experienced pilot/instructor at the controls. Probably zero would be my guess. The same can't be said for Robinson helicopters.

gulliBell: if you look at post #51 above, you'll see that in the data set studied, I identified in the "undetermined" category 3 Bell fatal accidents and 2 Robinson fatal accidents. Whether those are in-flight break-ups I can't say. There were also 2 Bell flights with mechanical difficulties (engine, transmission, etc.) that resulted in fatalities, but none like that for Robinsons.

[Bell_ringer]

according to the FAA civil aircraft registry, there are almost 3.5 times as many Robinsons as Bells registered: 2846 Robinsons of all types vs. 828 Bells of all types. Given the popularity in the US of Robinson helicopters for instruction, personal and light commercial use. could it be that the Bell fleet is working 3.5 times harder than the Robinson fleet?


I'd check those numbers. A simple search on the FAA registry has 1636 R44 variants and 1675 206 Variants, the numbers for the several other models they have are also significant..

(assuming the same level of incorrectness in the database for both manufacturers)

[aa777888]

This is the search URL I am using for Robinson:

FAA Registry - Aircraft - Make / Model Inquiry (http://registry.faa.gov/aircraftinquiry/AcftRef_Results.aspx?Mfrtxt=ROBINSON+HELICOPTER&Modeltxt=&PageNo=1)

That seems OK.

But, damn, the initial search I used for Bell was not a good one :(

In redoing this I tried to finesse the search, but the FAA website was not helpful. So I searched on each model number separately, added them all up, and got 3554 Bells of all types in the FAA registration database, which equates to a fleet strength of about 25% more than Robinson. I'm sure I missed one here or there, but close enough.

So now the bet on total fleet hours is a much more interesting one!

I'd happily pay for a beer if someone could trot out the annual hours for each fleet, bet or no bet.

[helicopter-redeye]

....breakup in flight with an experienced pilot/instructor at the controls.....

Don’t suppose you could point us to a couple examples of this in the UK? Thanks h-r

[Paul Cantrell]

I'm not sure how many Bell helicopters breakup in flight with an experienced pilot/instructor at the controls. Probably zero would be my guess. The same can't be said for Robinson helicopters.

So, I went through the accidents back to about 1994 (around when the R44 was certified. I ignored all the Bell 47 accidents, all the foreign accidents, and I think all engine failures. I was looking for accidents that came as close as possible to what you said: in flight breakup. Most of these are maintenance issues, but at least a couple were the way the pilot flew the aircraft which is probably what you were talking about... I ignored most loss of control, and hitting stuff with the main rotor or tail rotor, trying to just find cases where the pilot was flying along and the aircraft broke up. A couple of these are mast bumping due to the pilot...

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20170813X82426&AKey=1&RType=Prelim&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20160711X32921&AKey=1&RType=Final&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20080909X01417&AKey=1&RType=Final&IType=FA 206L1

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20100602X63138&AKey=1&RType=Final&IType=FA Bell 222

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20100831X75841&AKey=1&RType=Final&IType=FA 206L1

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20120116X72519&AKey=1&RType=Final&IType=FA 214

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001211X10786&AKey=1&RType=Final&IType=FA Bell 222

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001212X20136&AKey=1&RType=Final&IType=FA Bell 212

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001212X20659&AKey=1&RType=Final&IType=FA Bell 212

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20010105X00031&AKey=1&RType=Final&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001208X05655&AKey=1&RType=Final&IType=GA Bell 206L1

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001208X08741&AKey=1&RType=Final&IType=FA Bell UH-1B

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001212X16782&AKey=1&RType=Final&IType=FA Bell 206B

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001211X14108&AKey=1&RType=Final&IType=FA Bell 212

[Bell_ringer]

The first two have nothing to do with inflight breakup.
The first is a prelim report with no conclusion and indicates loss of control with an unknown cause.
The second was poor maintenance resulting in loss of control on landing.

Struggling to find the relevance.
Stopped reading after that..

[henra]

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20170813X82426&AKey=1&RType=Prelim&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20160711X32921&AKey=1&RType=Final&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20080909X01417&AKey=1&RType=Final&IType=FA 206L1

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20100602X63138&AKey=1&RType=Final&IType=FA Bell 222

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20100831X75841&AKey=1&RType=Final&IType=FA 206L1

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20120116X72519&AKey=1&RType=Final&IType=FA 214

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001211X10786&AKey=1&RType=Final&IType=FA Bell 222

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001212X20136&AKey=1&RType=Final&IType=FA Bell 212

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001212X20659&AKey=1&RType=Final&IType=FA Bell 212

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20010105X00031&AKey=1&RType=Final&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001208X05655&AKey=1&RType=Final&IType=GA Bell 206L1

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001208X08741&AKey=1&RType=Final&IType=FA Bell UH-1B

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001212X16782&AKey=1&RType=Final&IType=FA Bell 206B

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001211X14108&AKey=1&RType=Final&IType=FA Bell 212


Looking through all these accidents there is almost none initiated by simple handling errors or turbulence or completely unexplicable.
Almost in all cases there were either gross maintenance/ overlooked fatigue issues or other external factors (large Bird) preceding the Mast Bumping event. There is almost no straight forward low-g accident in there. Yes there were pilots in Vietnam who managed to do that with the fast and nimble Cobra but with the slower/bulkier Huey even in combat flight they were pretty rare (Tail shot off not counted in this category).

All statistics aside that is the really discomforting thing about quite a number of the fatal Robinson accidents (I don't care about those aircraft dinged in training -that is to be expected) that they happened with totally serviceable and often rather new aircraft with often experienced pilots in best flying conditions.

[Paul Cantrell]

The first two have nothing to do with inflight breakup.
The first is a prelim report with no conclusion and indicates loss of control with an unknown cause.
The second was poor maintenance resulting in loss of control on landing.

Struggling to find the relevance.
Stopped reading after that..

I was responding to gulliBell's assertion: I'm not sure how many Bell helicopters breakup in flight with an experienced pilot/instructor at the controls. Probably zero would be my guess. The same can't be said for Robinson helicopters.

He guessed zero. I gave 13 examples just going back to 1994... some of these are clearly maintenance, some of them are design problems with the Bell product, and some of them (the smallest number) are probably due to the way the pilot was flying the machine.

The first one indicates what looks like a tail boom chop including strikes from both the main and tail rotor, and which is consistent with the witness' reports of a spinning nose low approach to the ground. Not sure if you disagree with the fact that the tailboom got chopped, or maybe you don't consider that an "inflight breakup". We can ignore that one if you want.

The third one says:
They subsequently reported seeing components separate from the helicopter before it descended and impacted the ground. The helicopter came to rest in a corn field approximately 1.2 miles from the departure point. A postaccident examination of the helicopter revealed that an 8-foot section of one of the main rotor blades separated in-flight rendering the helicopter uncontrollable. which is certainly an in-flight breakup.

The next one, the Bell 222 actually mentions in-flight breakup: The helicopter was on a postmaintenance flight when it experienced an in-flight breakup about 8 minutes after departure and although it happened on a post-maintenance flight, if you read the report it was not a result of maintenance, but of a pin that was subject to hydrogen embrittlement.

The one after that I think I pasted an incorrect link, but the the 214 accident after that says There was no evidence of abnormal engine operation at the time of the accident or a failure of the tail rotor system or a major airframe structural component before the in-flight breakup. They have a theory about why it happened but the root reason couldn't be determined due to the post crash fire.

The one after THAT, the 222 quote: The helicopter experienced an in-flight break-up when it was traveling at about 130 knots at 960 feet above the ground. due to a fatigued pin quote: A factor was the manufacturer's dissemination of the pin which did not meet dimensional standards.
i.e. Bell screwed up.

The one after that, the 212:
They then observed the main rotor blades contact the tail area, and the aft tail boom and tail rotor separate. Shortly after this, the main rotor separated and the helicopter descended and crashed to the ground. i.e. an in flight breakup.

Another 212: The main rotor mast displayed evidence of a mast bumping event, with indentations corresponding to the blade stops. and the probable cause: the in-flight separation of the main rotor mast while in cruise flight following a mast bumping event. The reason for the mast bumping event was not determined.

The 407 after that seems to be a tail boom chop by the tail rotor... whether it "broke up" is conjecture since no-one was around to see it, but all but 3 feet of the tailboom was separated from the fuselage - I'd call that in flight breakup.

The 206L1 after that was a boom separation due to fatigue cracks in the attachment structure.

The next, a UH-1B the probable cause finding: A fatigue fracture in the main rotor mast, which resulted in an in flight separation of the main rotor from the helicopter.

The 206B after that was THE AIRCRAFT HAD EXPERIENCED AN INFLIGHT SEPARATION OF THE VERTICAL FIN AND SUBSEQUENT MAST BUMPING due to corrosion.

The last one, a 212 THE INFLIGHT SEPARATION OF THE MAIN ROTOR SYSTEM AS RESULTS OF THE
MAIN ROTOR STATIC STOP CONTACTING THE MAST FOR UNDETERMINED REASONS.

The relevance is that gulliBell postulated that zero Bells had broken up in flight with an experienced pilot at the controls, and I gave some examples of cases where that was wrong. I like Bells, I feel safe flying the B206B3 and B206L3, and given the chance to fly a 407, 222, 214, 212, or UH-1B I would, but to say that Robinson has all the in-flight breakups and other manufacturers do not is demonstrably not correct. I also am not trying to pick a fight with anyone... I'm just responding to a fairly extreme position with some data that says all manufacturers have issues with their designs...

[aa777888]

While I agree that four of the citations were probably not applicable, the remaining citations are all the exact sort of thing that would send Robbie haters into paroxysms of Robbie bashing.

Catastrophic, unexplained failures happen to all sorts of helicopters, not just Robinsons, as do catastrophic failures due to design and quality assurance errors on the part of the manufacturer. Hence the old joke: a million parts whirling around an oil leak, waiting for metal fatigue to set in.

Some might say all of the citations below are exceptions, not the rule. And Robinson's have a history, of that let there be no doubt. But at the current state of evolution of the designs, and SFAR 73, it would seem that, for the past two years anyway, performance and safety are comparable to other helicopters when operated in a manner consistent with lightweight, low inertia characteristics. At least based on US data. Outside of the US it would seem things are not so rosy. (Disclaimer: said conclusions admittedly based only on number of accidents and number of aircraft operating, no data on total fleet hours available.)


https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20170813X82426&AKey=1&RType=Prelim&IType=FA Bell 407

This accident is exactly the type of thing anyone would complain about with a Robinson. A sudden, unexplained, catastrophic failure.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20080909X01417&AKey=1&RType=Final&IType=FA 206L1

Blade spar failure and latent manufacturing defects in the blade, again, exactly the sort of thing complained about with Robinsons.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20100602X63138&AKey=1&RType=Final&IType=FA Bell 222

Catastrophic failure due to hydrogen embrittlement of an "unknown source". If this happened on a Robinson, there would be endless discussion about the usual suspects: Robinson quality control, etc.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20120116X72519&AKey=1&RType=Final&IType=FA 214

Another "mystery failure" of a critical flight control.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001211X10786&AKey=1&RType=Final&IType=FA Bell 222

Poor manufacturing QA on the part of Bell.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001212X20659&AKey=1&RType=Final&IType=FA Bell 212

Mast bumping due to unknown causes.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20010105X00031&AKey=1&RType=Final&IType=FA Bell 407

Loss of control for reasons undetermined, with evidence of tail boom blade strikes.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001208X05655&AKey=1&RType=Final&IType=GA Bell 206L1

Bell's inadequate SB inspection interval with respect to detecting tail boom fatigue cracks.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001208X08741&AKey=1&RType=Final&IType=FA Bell UH-1B

Main rotor mast fatigue fracture, well within life limits.

https://app.ntsb.gov/pdfgenerator/ReportGeneratorFile.ashx?EventID=20001211X14108&AKey=1&RType=Final&IType=FA Bell 212

Mast bumping for undetermined reasons.