What is the latest information re Bond's Loss of Rotor Head crash on the North Sea?

[SASless]

Last I heard the AAIB had determined "What" happened.....but have they determined "Why" it happened?

What measures have been put in place as a result of that tragic crash and have there been any significant findings since they were done?

Can we be assured the situation is resolved following technical improvements, procedural changes, or by other means?

[VeeAny]

Sasless expect the report soon.

I know those who are entitled to see it prior to publication have seen it and I think their comments where due back to the AAIB by end of July.

I guess it depends on whether any comments made by those people or companies will affect the content, as to how long it will take to release to the public.

[SASless]

It should make for interesting reading. We just don't expect MGB's to come apart anymore unless something very unusual acts to cause them to do so.

One would like to think these kinds of tragedies could be prevented as the industry matures.

[SASless]

Bond has settled with the Next of Kin of the Pilots killed in the crash.


Bond helicopter firm settles with partners of pilots killed in crash | Aberdeen & North | News | STV (http://news.stv.tv/north/193295-helicopter-firm-settles-with-partners-of-pilots-killed-in-north-sea-crash/)

[riff_raff]

"....The accident happened when the main rotor broke off, as a result gearbox failure, and severed the aircraft's tail boom....."

The description of the accident in the article seems a bit silly. The "main rotor broke off.....and severed the aircraft's tail boom". Once the main rotor separated from the aircraft, what significance does the impact with the tail boom have? Are we to believe that the aircraft would have been able to maintain stable flight had the departing main rotor not severed the tail boom?

Catastrophic structural failures of main rotor shafts/bearings should be an extremely rare event if modern design, manufacturing QA, and maintenance procedures are followed. Long before that main rotor shaft suffered structural failure, the MRGB HUMS should have given an indication of a problem.

[HeliComparator]

Long before that main rotor shaft suffered structural failure, the MRGB HUMS should have given an indication of a problem.

If only! As I understand it the defect originated in a planet gear which of course as well as rotating itself, is also travelling around the epicyclic. Therefore one point of the gear (where the crack was developing) follows a complex path which only repeats at relatively infrequent intervals. If you understand how the signal averaging techniques (used to extract data on a specific item using external sensors) works, you would know that this problem would result in very long acquisition times to get enough data for the signal averaging to work. That means lots of memory and a requirement to maintain stable flight conditions for a long time. This is not impossible, just difficult and thus not designed into HUMS technology whose concepts were developed in the 1990s.

One of the self-inflicted injuries of HUMS is that, whilst it is good, it is not a panacea and when an accident occurs that HUMS did to detect, it is ridiculed by the disbelievers. All the accidents that would have happened without HUMS are not taken into account.

[[email protected]]

But a crack in a gear should still change the vibration signature of the gearbox and at least hint that something is wrong - just as you know a bowl or cup is cracked because it sounds different when you tap or knock it, even if you can't see it and it hasn't broken yet.

Otherwise you are saying there is no method of detecting similar problems and the same failure could occur at any time!

[Hummingfrog]

Crab

the vibration signature of the gearbox

A gearbox doesn't have a single vibration signature it has hundreds depending on what flight regime it is experiencing. As HeliComparator said it developed in a gear which follows a complex path in the gearbox whose signature must be very complex.

HUMS forecasting is a bit like weather forecasting the more info you can get and the nearer the time to an event the better your forecast will be of that event.

It is a very good system and is getting better all the time as information is gathered but it is still at the stage of an early AMSTRAD compared to present day PCs.

The major clue to this failure of the gearbox was the flake of metal it made and the influence of magnets in the gearbox on finding flakes of metal.

HF

[HeliComparator]

Crab, I guess you don't understand how signal averaging allows the extraction of the vibration relating to a specific element (shaft, gear etc) within a gearbox. I suggest you look it up!

So yes, the same could happen again if the early warning sign of a chip is ignored. In many ways debris monitoring (chip detection etc) and HUMS (detection of non-debris releasing defects) complement each other to cover most, but not all, eventualities.

[Soave_Pilot]

I am with Hummingfrog on this one too...

Also in my view:

Taking an action of ditching a helicopter only because of a vibration is somewhat precipitated... Unless is something moderate to extreme of course.

Ditching a Helicopter only because of a MR chip light is also somewhat precipitated (as it could be a sensor failure).

Now... Ditching a Helicopter because of a MR chip light + vibration is something vey well explainable.

What sign did the crew have? I guess we will have to wait for the report...

[industry insider]

Soave

The report was published by the AAIB on November 24th 2011. Its an interesting read. HUMS is being developed to provide AAD but its a slow process. Does anyone do SOAP anymore in addition to HUMS and debris monitoring?

[DonQuixote23]

Could a possible action in the event of either an MR chip light or vibrations be to go down to very low altitude and slowly limp home? At least in that case if something goes totally pear-shaped the fall is survivable.

[Jetboxer]

DonQuixote23,

Could a possible action in the event of either an MR chip light or vibrations be to go down to very low altitude and slowly limp home? At least in that case if something goes totally pear-shaped the fall is survivable.

In this case, unfortunately, the crew had neither of these indications prior to a catastrophic failure.

http://www.aaib.gov.uk/cms_resources.cfm?file=/2-2011%20G-REDL.pdf

[HeliComparator]

II - although AAD is in being, it works by evaluating existing HUMS parameters. As far as I am aware there are no parameters for planet gear health, for the reasons explained, so unfortunately AAD would not help in this particular scenario.

DQ, in a word, no, not if survival was your intention.

[DonQuixote23]

"DQ, in a word, no, not if survival was your intention."

Due to? Not enough time to deploy the floats?

[Old Age Pilot]

Could a possible action in the event of either an MR chip light or vibrations be to go down to very low altitude and slowly limp home? At least in that case if something goes totally pear-shaped the fall is survivable

Due to? Not enough time to deploy the floats?

Surely common sense comes into it here? How low are you thinking of going? What height would you expect to be able to fall from without getting hurt?

[Jetboxer]

DQ,

I think HC is hinting to the fact that with a MGB Chip light, and vibrations (and other related warnings indicating an imminent failure of the gearbox) it would be wiser (if survival was your primary goal) to carry out a controlled ditching, pop the floats and man the liferafts - very well demonstrated by a Bond EC225 crew earlier this year.

Rather than....

Flying along slow and low, 'limping' home - During this 'limping home' stage if the MGB were to fail catastrophically, I doubt there would be much time to do much, let alone pop the floats. The change in attitude of the aircraft, I'm guessing, would be dramatic.

[DonQuixote23]

Jetboxer - thanks. What happens with a heli that ditches without the floats. Is it so top-heavy that it immediately flips around and sinks quickly?

[212man]

DonQuixote23 Jetboxer - thanks. What happens with a heli that ditches without the floats. Is it so top-heavy that it immediately flips around and sinks quickly?


Basically, yes. Search for G-TIGH for a tragic example.

[SASless]

This topic....Limp or Ditch....has been done to death before. The Consensus was "Ditch" anytime you have more than a simple single indication such as a Chip Light.

The original mindset was a gearbox would give you some warning .....but as it has been proven that is not always the case....then a controlled ditching is far safer than experiencing a Catastrophic failure while in any stage of flight at any altitude or airspeed combination.

[[email protected]]

HC, not the most helpful of answers!

However, from what I can see, signal averaging does exactly what we want - it identifies and amplifies vibrations that might otherwise be masked and lost in the 'noise' from correctly functioning parts of the gearbox. If they can do it with the human heart then a MRGB shouldn't be that tricky.

Since a MRGB will have a reasonably consistent 'signature' in the cruise (where most spend the majority of their time), anything that suddenly, or even gradually diverges from that norm should be questioned as it may be the portent of a failure.

Perhaps if you have more detailed information you might like to share it instead of being so dismissive.

[500e]

Was told some time ago that pilots would not understand the hums, even if it was in a simple form, I would have thought there was a way to show discrepancy's on a display against the average of a previous period.

[DonQuixote23]

Here's someone talking who really don't know much about the particular subject, but difficult part must be the signal (time-frequency) analysis. If you get that bit right, the user interface to inform the pilot cannot be a huge problem to solve. How is information displayed in todays HUMS systems?

Is it like 500e says that it actually shows frequency diagrams over time (if that is what he is saying :) Sounds like hard work to manually make sense of that.

[HeliComparator]

HC, not the most helpful of answers!

Perhaps if you have more detailed information you might like to share it instead of being so dismissive.

Since you asked so nicely.....

Trouble is, not that easy to explain to someone without an understanding of the signal processing involved in HUMS but I will try, though you may get bored before the end!

Accelerometers are mounted on the outside of the MGB, so that they do not create an additional hazard by their presence within the MGB. This means that any one sensor picks up vibration from a number of sources - it is just a mush. However the trick is to use the information about the gear ratios and a speed sensor such as N2, to start digitally recording the mush, and stop again when the shaft / gear in question has completed one full turn. Then start recording again for another full rotation. Do this perhaps 100 times and then lay all the recordings on top of each other. In doing so, since the vibration signature of the item in question is always the same in each recording (ie starting and finishing at the same place) the signal is reinforced with each recording. By contrast the signals coming from other elements going at different rotational speeds are not correlated because the signal from them for each recording is different. So when you add them up they just stay as low level mush.

Now you have extracted the signature for the element in question, you can do clever things such as run through a Fast Fourier Transform (FFT - converts into the frequency domain, a bit like a spectrum analysis). Then you can remove the specific frequencies you are expecting from the teeth meshing frequency etc so you are left with a low level noise, some of which might be "unexpected". By running through an inverse FFT you go back to the time domain (same as the angular rotation domain) to see where the noise emanates from, whereupon you could for example see that one tooth of the gear is noisy, indicating a possible cracked tooth.

So, the trouble with all that for a planet gear, is that for it to work you have to collect the 100 or so recordings (the more the merrier) of complete rotations of the system in question. That is from when the planet gear is in a specific location and rotational position, to when it is again in exactly the same location and rotational position. Times 100. Depending on the number of teeth, this can take very many rotations of the sun gear - which might only be doing 265 rpm - for each recording. Then repeat for each planet gear, resulting in a very long acquisition time, during which the heli must remain in a stable condition.

So whilst not impossible, consideration has to be given to the practicalities of requiring long periods in the cruise to gather data. Current systems take 20 mins or so, and whilst this time could be longer for some N Sea routes, the feeling at the time was that the system should work for a wide variety of operations, not just those with long sectors. Also at the time, memory was an issue and the prospect of sufficient storage to allow the recordings was daunting.

So yes it could be done, new DAPUs could be designed, built and certified with modern memory capabilities that would work on long cruise sectors, but so far that hasn't happened. Mostly down to cost of course.

HC

[HeliComparator]

Was told some time ago that pilots would not understand the hums, even if it was in a simple form, I would have thought there was a way to show discrepancy's on a display against the average of a previous period.

There is a way, but when flying over hostile surface such as N Sea, the consequences of a false warning creating a ditching scenario resulting in loss of life etc, is too great. The sensors for HUMS live in a very nasty environment with vibration, heat and dirt, and false warnings remain a problem.

[SASless]

500E....for most pilots....a simple Red/Green light display would be about as complicated as one would need. Simple design, simple display, and very few options for a Pilot to understand.

Do we really care about everything else that makes the light illuminate or do we just want a warning of things being not quite right?

The CAA left to its own devices, will have Pilots writing technical papers (at no small cost too) on the design, manufacturing, and science that underlies the whole concept....rather than just putting the light in the cockpit and allowing us to react to the thing.

I do get a certain amount of joy out of Crab and HC having a go at one another....and will settle for that bit of pleasure while waiting for HUMs to mature yet another Generation in the process.

A good question is begged......"Can we ever with absolute certainty forecast/detect/identify/prevent all of the causes of a Catastropic MGB failure?"

Assuming the answer is a negative....at what point do we spend more money than it is worth and thus waste that money rather than spending the same amount of money on other more simple improvements that will provide for an equal increase in safety in other areas that cause deathes.....and thus be ahead of the game by doing that instead of pushing HUMs as the best way to cut down on Fatal Accidents?

[HeliComparator]

Assuming the answer is a negative....at what point do we spend more money than it is worth and thus waste that money rather than spending the same amount of money on other more simple improvements that will provide for an equal increase in safety in other areas that cause deathes.....and thus be ahead of the game by doing that instead of pushing HUMs as the best way to cut down on Fatal Accidents?

Can't disagree with that, and of course horses, water and drinking spring to mind...

You can have all sorts of fancy diagnostic tools such as HUMS, AAD, chip detection, SOAP etc but they are no use at all if the operator's technicians do not pay attention to what they are trying to tell him!

HC

[[email protected]]

HC - a very informative answer, thank you and I wasn't bored at all:)

The explanation of the required capture time for the planet gear signature was the bit I hadn't fully grasped - I suspect if I was to ask the question about our HUMS I might get the same answer from our engineers.

Our biggest problem with HUMS is sorting the wheat from the chaff when every sortie produces so many cautions and our F700s have lots of HUMS related defects (due to inaccurate HUMS accelerometers and the like) - it is easy to lose faith with what should be, and often is, a very powerful tool.

[riff_raff]

You can have all sorts of fancy diagnostic tools such as HUMS, AAD, chip detection, SOAP etc but they are no use at all if the operator's technicians do not pay attention to what they are trying to tell him!HeliComparator,

Indeed, there are limitations to what types of failures monitoring systems like HUMS or magnetic chip detectors can prevent. Instrumentation like chip detectors or vibration monitors (accelerometers) are only capable of detecting failures after they have initiated. But these types of failures are usually not catastrophic in nature. Vibration monitoring systems can identify which drivetrain component (such as a gear or bearing) is failing based on meshing or passing frequency. But this also requires a detailed acoustic characteristic model of the drivetrain to compare against.

The approach used for flight critical parts like gears, main rotor shafts, hubs, etc. is to design, manufacture and maintain the part such that a structural failure in service is never going to occur (in theory). This means a having detailed fracture control plan for the service life of these components. Unfortunately, even the best QA and maintenance procedures are only effective if they are adhered to.

[chutedragger]

I am not being insensitive to the pilots experience or ability in this situation. It is more of a question or shock and awe of the company. I am not from that part of the world but...1350 hours pic and 100 pic ?? For the crew is somewhat surprising. You cant sling a bucket with less than 1500 hrs in most parts of the world!!!

Is this normal for bond...Bristol? I am pretty sure chic is 3000+

[farsouth]

Chutedragger - the majority of (non ex-mil) pilots on the UK North Sea will have gone straight from training (150-200 hours on light helis, maybe 100 hours of PIC), to the left seat of a large offshore type. After that, the next PIC hour they will log will be their first hour after getting their command, so on that day they will be a Captain with maybe 100 hours PIC on an R22 and zero hours PIC on type - they will however, have around 3000 hours total and maybe 2900 hours on type (or similar category).

(Some oil companies insist on minimum P1 hours requirements on type for pilots on their contracts, maybe 500 - this causes problems for the operators with newly promoted captains, Catch-22, how can you get the 500 hours P1 on type if the customers won't let you fly for them........)

[Sir Korsky]

Some excellent info HC, thanks for taking the time.:ok:

[Fareastdriver]

Catch-22, how can you get the 500 hours P1 on type if the customers won't let you fly for them........)

One very major oil company refused to use the S76A when it first arrived in the North Sea because non of the pilots had 500 hrs pic on them.

[SASless]

Oil Company Aviation Departments have never been accused of being logical, knowledgeable, or having any great amount of commonsense.

They do talk a good line of bull**** however!

But....they do pay the bill!

Offshore flying is not rocket science....and converting from one type of helicopter to another is not exactly a big deal.....but there are many in the Helicopter industry that have made a career out of making them both difficult for very personal and less than justifiable reasons.

Would you rather have a long serving 15,000 hour pilot with 10 hours in type.....or a low hour new hire Pilot with 500 hours on type?

[Geoffersincornwall]

SAS

It's no longer the case that you can use flight hours as a measure of 'competence'.

The problem is that your 15,000 hour man may in fact have 15,000 times the same hour (Please note the word 'may' before you kick-off) and the young lad with a thousand hours can do the job extremely well because he was able and had been well trained and supervised during his formative spell as a commander.

We have to get away from the mindset that the guy with thousands of hours is automatically better than the one with less. Take a look at his competence then make your judgement. Unfortunately, as you imply, the oil companies (not the ones with aviation departments but those without in my experience) have perpetuated the myth that competence can be measured by the number of flight hours. Shell had a scheme by which low time people could be used subject to evaluation so there was at least a little flexibility.

Competence requires an effective training regime and it presupposes that it includes scenario-based LOFT training by training staff that are themselves truly competent.

G.

[HeliComparator]

Would you rather have a long serving 15,000 hour pilot with 10 hours in type.....or a low hour new hire Pilot with 500 hours on type?

Depends - if the 15,000 hr pilot was brought up on steam driven VFR with lever, knobs and pulleys, but the type was a modern glass-cockpited IFR machine in bad weather, and he hadn't really bothered to pay attention during the groundschool etc and was passed by his examiner because he "must be OK with 15,000 hrs" then maybe I would prefer the new hire with 500hrs on type and a good understanding of how all the systems worked, and their failure modes etc.

As Geoffers says, hours is not a good indicator of competance and certainly hours not in the correct role (aviation being very role-specific) is often not very helpful and can be counter-productive. "When I worked for X we did it like this" - X of course being an onshore VFR single pilot company when he is now flying offshore multipilot IFR etc.

But in answer to the original question, as farsouth says, the captain may have very little P1 time when he gets his first command, but he has lots of experience in role and has had plenty of time to study those who did it well, and those who did it badly, when he was a co for 3000hrs.

HC