Another Robinson crash

[aa777888]

Originally Posted by Bell_ringer

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]

Originally Posted by 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.

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]

Originally Posted by aa777888

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

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]

Originally Posted by 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.

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/Re...relim&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA 206L1

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 222

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA 206L1

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA 214

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 222

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 212

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 212

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=GA Bell 206L1

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell UH-1B

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 206B

https://app.ntsb.gov/pdfgenerator/Re...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]

Originally Posted by Paul Cantrell

https://app.ntsb.gov/pdfgenerator/Re...relim&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA 206L1

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 222

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA 206L1

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA 214

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 222

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 212

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 212

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 407

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=GA Bell 206L1

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell UH-1B

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 206B

https://app.ntsb.gov/pdfgenerator/Re...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]

Originally Posted by 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..

I was responding to gulliBell's assertion:

Originally Posted by 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.

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/Re...relim&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/Re...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/Re...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/Re...Final&IType=FA 214

Another "mystery failure" of a critical flight control.

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 222

Poor manufacturing QA on the part of Bell.

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 212

Mast bumping due to unknown causes.

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 407

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

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=GA Bell 206L1

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

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell UH-1B

Main rotor mast fatigue fracture, well within life limits.

https://app.ntsb.gov/pdfgenerator/Re...Final&IType=FA Bell 212

Mast bumping for undetermined reasons.