Another Robinson crash

[9Aplus]

http://www.pprune.org/rotorheads/600...ml#post9916145
or here
HeliHub.com Guimbal

[aa777888]

Originally Posted by 9Aplus

http://www.pprune.org/rotorheads/600...ml#post9916145
or here
HeliHub.com Guimbal

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]

Originally Posted by [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.

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]

Originally Posted by [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.

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

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:

Originally Posted by [email protected]

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?

Originally Posted by aa777888

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.

Originally Posted by 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?

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

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]

Originally Posted by Paul Cantrell

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]

Originally Posted by Bell_ringer

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_poli...l_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

[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]

Operational tempo

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]

Originally Posted by Hot and Hi

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]

Originally Posted by aa777888

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]

Originally Posted by Bell_ringer

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]

Originally Posted by aa777888

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.