Helicopter down outside Leicester City Football Club

[Sky Sports]

I've inspected dozens of rotor blade birdstrikes and one thing is common, you will always find bird remains on all the blades. Looking at the photo of the tail rotor on the ground, there are no bird remains at all.

[henra]

I've seen a sea gull descend into a turning sea king main rotor. The resulting feather explosion was impressive. A big goose and all those lights? Unlikely IMHO.
Fair point! A goose- "explosion" would probably indeed have been visible in the video although the tail rotor will likely not generate quite the same effect as the main rotor..

[Torquetalk]

Zerospeed autos were done very frequently to confirm tail rotor rigging, did many as a FM.

This was about dong pedal turns through 180 degreees (or more) whilst established in a zero speed auto.

[Michael Gee]

Sky Sports, when you say I assume you're looking at the picture that VintageEngineer offered (.pdf below).

The strange thing about that picture is that it's titled 'GGSKP TailRotor....". But this aircraft was GVSKP...

Probably not significant? But strange.

airsound

The blade at 12 o'clock in picture has what appears to be feathers/remains on the leading edge

[KarlADrage]

The blade at 12 o'clock in picture has what appears to be feathers/remains on the leading edge
Looks like strands of carbon fibre to me?

[NRDK]

He added: 'Pilots are trained for this. It is survivable with the appropriate technique. It shouldn't be catastrophic'.

But aviation expert Jim Rowlands, a former RAF Puma crew member, told The Sun: 'There's no real coming back from that. The only way is down.

'The pilot has clearly done an incredible job, really'



Err, Mr Rowlands... we beg to differ on your expert conclusions. Tragic though the outcome was. Not only did the “ incredible job”, that being to steer the unfortunate passengers away from a school, orphanage, hospital and LGBT parade, but it also resulted in total loss of life and aircraft...really! True, the only way is down, but how you allow gravity to dictate your arrival does also involve a pilots input in most cases, including this one.

[cyclic]

Thanks for reminding me of the zero speed 180 degree auto Crab. I was just about over it.

[SASless]

Zero Airspeed Auto with pedal turns.....normal part of every CoA Airtest on Bell 212's for sure.

[gulliBell]

..Does the AW169 type have a cockpit voice recorder?
..Don't Leonardo fit crash proof fuel tanks to this new type of a/c?


Yes, to both.

[gulliBell]

This incident is surely the worst case scenario that any helicopter crew could experience....

Yep, it's towards the top. Trumped by MGB seizure / MR separation in-flight.

[megan]

Zero Airspeed Auto with pedal turns.....normal part of every CoA Airtest on Bell 212's for sureNever heard of the procedure. Was this a routine procedure following tail rotor replacement, and apply to all helos? We had what I considered top flight maintenance, but all I ever recall doing was auto RPM checks, irrespective of type, military and civil.

[SASless]

UK CAA Certificate of Airwothiness Test Flight Requirement.

The CAA had some interesting requirements for the CoA.

[[email protected]]

Cyclic - it was 90 degrees to the right to check TR rigging in low speed (below 30 kts) auto, but you are right, it wasn't very comfortable:ok:

Myra - agreed, if he was doing the same confined area departure as in the 139 he would have an extra load on the TR by being cocked off to the left in order to keep the LS in sight - but why the removal of that yaw input at TDP would then cause a failure escapes me.

[Mitchaa]

If I'm not very mistaken it can't possibly be a TR failure as many are suggesting because G-VSKP was clockwise-rotored (tail-rotor on right, unlike G-LCFC which appears in some pics) and the spiral down was in the direction of TR being the main force. So as others have mentioned issues such as TR hardover or main rotor vortex ring state are possible.

AW169 Main rotor spins in an anti clockwise rotation. Tail rotor in a clockwise. Aircraft spins in a clockwise rotation on the way down.

Vortex ring wouldn't cause that effect, it would just simply plummet.

[gazpad]

If I'm not very mistaken it can't possibly be a TR failure as many are suggesting because G-VSKP was clockwise-rotored (tail-rotor on right, unlike G-LCFC which appears in some pics) and the spiral down was in the direction of TR being the main force. So as others have mentioned issues such as TR hardover or main rotor vortex ring state are possible.

Both ships have counter-clockwise turning rotors, the tail rotor type on the G-LCFC is a pusher and on G-VSKP was a puller.

[obnoxio f*ckwit]

Ivorget

If I'm not very mistaken...

I think you might be...

[[email protected]]

All the AW 1*9 family have puller TR on the right hand side and all have MR rotation anti-clockwise when viewed from above.

[Jackonicko]

Simple question for my betters:

Would a lift into a low hover transitioning into a more 'horizontal' take off be inherently safer than a departure like this one? (Given a suitable obstacle free 'runway'/take off path....)

And would a suitable take off run have been available outside the stadium?

[chopjock]

Vortex ring wouldn't cause that effect, it would just simply plummet.

VR may not cause that effect, but if in VR with no TR drive I'm sure it would rotate. I should think this incident could well have entered VR on the way down without tail rotor drive. It had a high ROD and drifted down wind. We don't know about the power setting yet...

[ShyTorque]

Simple question for my betters:

Would a lift into a low hover transitioning into a more 'horizontal' take off be inherently safer than a departure like this one? (Given a suitable obstacle free 'runway'/take off path....)

And would a suitable take off run have been available outside the stadium?

What do you mean by "inherently safer"? If the t/r drive was faulty (if that is what caused this, hopefully initial findings will soon be made public) the accident might have occurred at a slightly different time but would possibly have put the aircraft down in a less fortunate place for those on the ground. Helicopters are designed to operate vertically, btw! The departure flown appears to have followed a certified Category A / Class 1 profile so it should have been as safe as any other.

[falcon900]

Does anyone have a schematic of the tail rotor driveshaft and gearbox assemblies?

[chopjock]

What do you mean by "inherently safer"? If the t/r drive was faulty (if that is what caused this, hopefully initial findings will soon be made public) the accident might have occurred at a slightly different time but would possibly have put the aircraft down in a less fortunate place for those on the ground. Helicopters are designed to operate vertically, btw! The departure flown appears to have followed a certified Category A / Class 1 profile so it should have been as safe as any other.

Presumably he means that had the climb out been more forwards, gaining airspeed, translational lift and a headwind asap there would be less stress on the TR and for a shorter exposure time...

[Fareastdriver]

The 169 has a winching capability. That punishes the tail rotor far more than a Cat A departure.

[Thomas coupling]

Chopjock.

You'll never change will you? After years of posting on rotorheads, listening to the advice of others - you still talk complete and utter bo**ox, don't you?

[Hughes500]

TC

Sorry Chopjock is correct, if you actually care to read the post Chop was referring to you will find Chop's answer is strictly correct. Unless you would prefer to be at 400 ft with no forward airspeed when the Tr assy takes a holiday. Personally I would take lower and probably doing around 60 to 80 kts ( that he would have arrived at in the time to go vertical to 400 ft.) At least your stabilisers would be doing something.

[SASless]

A question for you Legal Scholars posing as Helicopter Pilots.....the British way of doing a Confined Area Takeoff (I learned it as a Towering Takeoff) differed from the American way of doing the same thing (each used the same power) is far different from the various CAT A, Perf Class One (or whatever you are calling things this week).

Instead of this backwards and up to 400 feet (or so) as we saw used.....what if an old fashioned Towering Take Off had been used from as far downwind as possible and the aircraft accelerate much lower but clear of obstacles.....could Vtoss and Vbroc been achieved much quicker?

What Rules, Regulations, etc.....prohibit such a Takeoff like that a situation as is under discussion?

Are Rules getting ahead of reality and causing greater risk instead of making flying safer?

[Bosbefok]

All the AW 1*9 family have puller TR on the right hand side and all have MR rotation anti-clockwise when viewed from above.
Except for the 109 and 119, which push

[Art of flight]

A question for you Legal Scholars posing as Helicopter Pilots.....the British way of doing a Confined Area Takeoff (I learned it as a Towering Takeoff) differed from the American way of doing the same thing (each used the same power) is far different from the various CAT A, Perf Class One (or whatever you are calling things this week).

Instead of this backwards and up to 400 feet (or so) as we saw used.....what if an old fashioned Towering Take Off had been used from as far downwind as possible and the aircraft accelerate much lower but clear of obstacles.....could Vtoss and Vbroc been achieved much quicker?

What Rules, Regulations, etc.....prohibit such a Takeoff like that a situation as is under discussion?

Are Rules getting ahead of reality and causing greater risk instead of making flying safer?

I must admit that during my time with Army flying, I was always a little puzzled watching civil helicopters performing all sorts of convoluted and painfully slow departures when we just took off into wind and transitioned as quickly as possible, then along the years we started to introduce committed calls at various airspeed and heights in twins. Leaving the military and starting police and corporate flying introduced a whole section of the flight manual to be observed depending on aircraft weight, helipad size, obstructions,....etc. Explaining to passengers why I was not just flying forward became part of the pre take of drills at one particular base, just to head off the inevitable question halfway up to TDP!

[malabo]

SASless, it is a cart/horse question on regulation/performance profiles and which comes first. There are lots of risks and hazards in helicopter flying only some of which are addressed by regulation. And those tend to be the quantifiable ones. Easiest is the airline model where the worst that can happen is an engine failure, and so that is then applied to helicopter and the regulators come up with different standards, exposures, etc. Some, like EASA, have more focus on compliance to OEM flight test certification procedures than others. In our Wild West view of confined, the greatest risk is hitting something, in the EASA view or PC1, it is the first engine failing (the second one never fails). So the certification authorities go back to the manufacturers and say "give us the numbers and performance charts, and publish them in the RFM". Now over to sales where performance sells, so the manufacturer uses their test pilots to develop OEM recommended procedures to maximize performance and payload, regardless of the real-world additional risks introduced. Two examples: the back up profile in a true "confined" area where you might actually hit something; some of the PC1 runway takeoffs where the TDP is an altitude instead of an airspeed. When I first flew S76, the PC1 takeoff profile was like a "cobra" maneuver, accelerate to a certain speed, balloon up and level, accelerate some more and then climb - just the thing not to do on a black night in monsoon rain with a new national copilot.
Anyway, a horse beat to death, and there are many on this forum (such as JimL) that can explain it much more clearly than I can. Needless to say, in todays world nobody will risk any SOP other than the OEM provided one, to the point that even where there are obvious flaws operationally, like the original AW139 offshore helideck with the too rapid climb through 20', we will fly a far riskier profile until the OEM can come up with a published revised profile. And yes, in the past we had free rein to make those up and apply them ourselves.

[[email protected]]

Except for the 109 and 119, which push good point bosbefok - I was just thinking of the 139, 169 and 189 and forgot about the 109 and 119:ok:

[henra]

Chopjock.
You'll never change will you? After years of posting on rotorheads, listening to the advice of others - you still talk complete and utter bo**ox, don't you?
Hmm, I'm not sure I quite understand what exactly is b*****ks with @Chopjocks remark? Reducing the time spent at zero forward speed will reduce the time spent in very unhelpful conditions when encountering a TR drive failure. Any forward speed will unload the TR, thereby reducing torque effect and will additionally increase effectiveness of the fin. At >50kts there is a reasonable fighting chance in case of a TR drive failure. At zero kts not so much.

[RVDT]

Reducing the time spent at zero forward speed will reduce the time spent in very unhelpful conditions when encountering a TR drive failure. Any forward speed will unload the TR, thereby reducing torque effect and will additionally increase effectiveness of the fin. At >50kts there is a reasonable fighting chance in case of a TR drive failure.

And maybe not?

In the current designs with very small vertical surfaces be aware they virtually have no fin or it is very weak in effect -

Phoinix
8th Dec 2015, 13:16
I just finished my recurrent on the 412 at DFW South location. It's a brand new sim capable of 412EP with EFIS, Fast Fin and 4 axis AP. Extremely detailed visuals and updated flight data. The later was a huge surprise.

The instructor gave us a tail rotor drive shaft failure... Surprise surprise, the 412 is not capable of flight at any speed, Fast fin or not. If you enter an autorotation fast enough your only option is to follow it through the right turn, flaring at about 100-ish ft and of course than the left yaw comes that will turn you about 90º. So the flyaway no longer possible they teach to auto immediately and follow it through the right yaw.

I was on the old 212 sim and slightly newer 412 sim some years ago and I remember you could clearly fly away at a low power setting at vy.

[helimutt]

It is now exactly a week since the accident happened. Short of brief statements by the AAIB telling people what they already knew, there has been what can only be described as a deafening silence with regard to the cause. Would we be correct in thinking that, due to zero statements regarding the mechanical causes of this tragic accident, it can be assumed that the aircraft didn’t suffer a mechanical malfunction ? Or is this normal to have no word, even if it was found to be say a mechanical defect ? Obviously I’m not saying it was, but I seem to recall in previous events, that a failure of a particular item on an aircraft would render that type grounded until further investigation could rule it out. By not having any AD or SB issued, is it fair to say that the AW 169 has not suffered a catastrophic mechanical failure, but the cause is more likely to be external forces of some description, (drone strike) or pilot error? (I doubt it’s pilot error but that we have no details whatsoever yet)

[Thomas coupling]

Why is anyone quizzing the CAT A departure? In commercial ops it is a requirement not an option. So debating whether a takeoff profile other than this, is better - is a load of Bo**ox.

The pilot initiated a standard departure for the size of the site.

The probable causes now remain:
Part of the TR assembly failed and departed flight.
Something struck the tail area causing a catastrophic failure.

Once an aircraft enters a developed TR failure flight path (rotating) NOTHING the pilot does to recover (with the cyclic) will resolve the issue simply because the pitch/roll datums continuously change [as described earlier very succinctly].
The suggestion that the pilot fought to steer clear of people or property is wishful thinking At this stage in the flight, the pilot(s) became a passenger.

[Non-Driver]

It is now exactly a week since the accident happened. Short of brief statements by the AAIB telling people what they already knew, there has been what can only be described as a deafening silence with regard to the cause. Would we be correct in thinking that, due to zero statements regarding the mechanical causes of this tragic accident, it can be assumed that the aircraft didn’t suffer a mechanical malfunction ? Or is this normal to have no word, even if it was found to be say a mechanical defect ? Obviously I’m not saying it was, but I seem to recall in previous events, that a failure of a particular item on an aircraft would render that type grounded until further investigation could rule it out. By not having any AD or SB issued, is it fair to say that the AW 169 has not suffered a catastrophic mechanical failure, but the cause is more likely to be external forces of some description, (drone strike) or pilot error? (I doubt it’s pilot error but that we have no details whatsoever yet)



It's actually pretty rare to ground all examples of a type without some pretty solid evidence there have been multiple failures in the same mode across at least two incidents. The wreckage only departed the scene yesterday and the FDR could (par example) indicate TR performance loss without an immediate and obvious cause without further forensics.

[chopjock]

Tc
Why is anyone quizzing the CAT A departure?

I'm questioning it because it didn't work very well here did it? Cat A PC1 is so focused on one of two engines failing it completely disregards the extra exposure to the one and only tail rotor.

[obnoxio f*ckwit]

It is now exactly a week since the accident happened. Short of brief statements by the AAIB telling people what they already knew, there has been what can only be described as a deafening silence with regard to the cause. Would we be correct in thinking that, due to zero statements regarding the mechanical causes of this tragic accident, it can be assumed that the aircraft didn’t suffer a mechanical malfunction ? Or is this normal to have no word, even if it was found to be say a mechanical defect ? Obviously I’m not saying it was, but I seem to recall in previous events, that a failure of a particular item on an aircraft would render that type grounded until further investigation could rule it out. By not having any AD or SB issued, is it fair to say that the AW 169 has not suffered a catastrophic mechanical failure,

I’ve just picked on this individual post because it sort of illustrates my point; absolutely no criticism of it or the poster is intended.

Is it a particular helicopter thing to demand groundings the moment something happens?

On Monday a 737 crashed into the sea killing everyone on board, but I’ve yet to see any calls for 737s to be grounded.

In 2014 a 777 vanished without trace in the Indian Ocean, but I saw no calls for the 777s to be grounded, or questions about lack of emergency ADs/ASBs?

Three weeks after the 2016 EC225 crash in Norway, an Egyptian A320 crashed into the Med, with total loss of life. The cause is (AFAIK) still not known, yet our oil workers were happy to fly to Aberdeen on an Airbus A320 the next day before refusing to fly on an Airbus EC225.

What is it with helicopters that we have to react this way when our FW cousins do not?

[SASless]

The probable causes now remain:
Part of the TR assembly failed and departed flight.
Something struck the tail area causing a catastrophic failure.

Shake your Magic Eight Ball one more time and decide which it was so we can pass that news along to the AAIB so they can move on to other accidents.

[mickjoebill]

The probable causes now remain:
Part of the TR assembly failed and departed flight.
Something struck the tail area causing a catastrophic failure.

I take it that because it hasn’t been discussed, the video excludes the possibility of a stuck pedal?


mjb

[bumpthump]

I’ve just picked on this individual post because it sort of illustrates my point; absolutely no criticism of it or the poster is intended.

Is it a particular helicopter thing to demand groundings the moment something happens?

On Monday a 737 crashed into the sea killing everyone on board, but I’ve yet to see any calls for 737s to be grounded.

In 2014 a 777 vanished without trace in the Indian Ocean, but I saw no calls for the 777s to be grounded, or questions about lack of emergency ADs/ASBs?

Three weeks after the 2016 EC225 crash in Norway, an Egyptian A320 crashed into the Med, with total loss of life. The cause is (AFAIK) still not known, yet our oil workers were happy to fly to Aberdeen on an Airbus A320 the next day before refusing to fly on an Airbus EC225.

What is it with helicopters that we have to react this way when our FW cousins do not?
Disclosure: I am not a pilot of any sort. I am a retired oil worker, and was in the N Sea since the 70s in the days of Bristow, BA, and B Cal. I know it ages me.
To try and answer the question, I think much of it is simply “perception”. Be it U.K. or US, I think we hold our carriers and their pilots and ground staff in such high regard, that an incident of this kind makes us feel that questioning the air worthiness of the aircraft is our first legitimate port of call. When incidents occur with operators from what we see as either third world or countries that we perceive not to maintain the standards we do, then there is a tendency to consider pilot error or low grade maintenance to be a primary factor. Rightly or wrongly, that tended to be the viewpoint back in the 70s, 80s and 90s. Having flown with operators in SA and Africa, there were plenty of moments when that bias was re-inforced.....rightly or wrongly.

[jimjim1]

What is it with helicopters that we have to react this way when our FW cousins do not?

https://www.reuters.com/article/us-aviation-safety/2017-safest-year-on-record-for-commercial-passenger-air-travel-groups-idUSKBN1EQ17L

"2017 safest year on record for commercial passenger air travel
Airlines recorded zero accident deaths in commercial passenger jets last year,"

Probably carried more people in the first hour of 2017 than the entire global helicopter industry in the whole year. Someone might be able to work it out properly.

Helicopters are not as safe.

The aforementioned helicopter passengers seem to be behaving quite rationally.

Jet airliners and operations have proven themselves safe. Helicopters - still some way to go it seems.

[gulliBell]

I take it that because it hasn’t been discussed, the video excludes the possibility of a stuck pedal?

Yes, not stuck pedal. Stuck pedal never causes you to fall out of the sky.

[Twist & Shout]

I’ve just picked on this individual post because it sort of illustrates my point; absolutely no criticism of it or the poster is intended.

Is it a particular helicopter thing to demand groundings the moment something happens?

On Monday a 737 crashed into the sea killing everyone on board, but I’ve yet to see any calls for 737s to be grounded.

In 2014 a 777 vanished without trace in the Indian Ocean, but I saw no calls for the 777s to be grounded, or questions about lack of emergency ADs/ASBs?

Three weeks after the 2016 EC225 crash in Norway, an Egyptian A320 crashed into the Med, with total loss of life. The cause is (AFAIK) still not known, yet our oil workers were happy to fly to Aberdeen on an Airbus A320 the next day before refusing to fly on an Airbus EC225.

What is it with helicopters that we have to react this way when our FW cousins do not?

I’m pretty sure if there was video of both wings falling off a well maintained and gently flown 737/777/A320, there would be calls to ground the type.

[Gustosomerset]

The pilot initiated a standard departure for the size of the site.

At the risk of annoyance, a number of eyewitnesses and other videos appear to be indicating that the departure was not typical (standard?) for that site. Legal, within regulations, etc, etc, but possibly not normal. For the lack of any other evidence I still wonder if there might have been something about the height of the departure that offers a clue to what subsequently went wrong.


The probable causes now remain:
Part of the TR assembly failed and departed flight.
Something struck the tail area causing a catastrophic failure.

Statistically, is it in fact more or less just as probable that other causes remain to be considered - however apparently unlikely - i.e. pilot incapacity, sabotage, etc?

[gulliBell]

...Instead of this backwards and up to 400 feet (or so) as we saw used.....what if an old fashioned Towering Take Off had been used from as far downwind as possible..

Yep, I reckon. Countless times trying to get out of a tight spot in the boonies, back it up as far as you can go, get some airspeed whilst still in ground effect and then zoom climb it out at best angle. Many of those you'd never get out vertically, you just run out of puff before finding clear air above the trees.

[gulliBell]

..For the lack of any other evidence I still wonder if there might have been something about the height of the departure that offers a clue to what subsequently went wrong.


Yep, I'm wondering the same thing, why so high? Doing rejected elevated heliport night takeoffs in a S76 from 60' CDP is a pretty harrowing experience on the way down. I'd be uncomfortable being needlessly exposed any higher without airspeed.

[SASless]

Statistically, is it in fact more or less just as probable that other causes remain to be considered - however apparently unlikely - i.e. pilot incapacity, sabotage, etc?

With the scant information available to the public at this point....Commonsense alone indicates considering all possible causes to be the bett4er course.

Watching video's taken from several perspectives does tend to point one's interest in one direction but absent more definitive information pointing a finger at a cause at this time is pure speculation.

[Aucky]

Yep, I'm wondering the same thing, why so high? Doing rejected elevated heliport night takeoffs in a S76 from 60' CDP is a pretty harrowing experience on the way down. I'd be uncomfortable being needlessly exposed any higher without airspeed.

The only 169 profile suitable to this stadium which factors obstacle clearance is the variable TDP helipad. The TDP is 115ft + the height of the obstacle in your takeoff path so I’d guess a minimum of 250-300ft. The single engine failure before TDP is a not an overly ‘dynamic’ manoeuvre unlike some types. You need good references through the chin window and you fly back down the same path with up to 192% TQ available.

[Sir Niall Dementia]

Yep, I'm wondering the same thing, why so high? Doing rejected elevated heliport night takeoffs in a S76 from 60' CDP is a pretty harrowing experience on the way down. I'd be uncomfortable being needlessly exposed any higher without airspeed.

I agree with you totally, the vertical profile in the S76 is and aggressive manouvre from the start, and several aircraft have been damaged practising the reject. In fact the RFM actually states that you should go light in the seat when you drop the collective.

The back up profile as used in this case, and on most AirBus helicopters actually is quite gentle. You have power in hand (it should never need full power until you rotate into forward flight), keep the take-off point in view all the time and the reject is a reduction in collective to contain the power (not slamming it down) drop the nose around 8 degrees and the aircraft flies back to the take-off point slowly and under full control, over the pad use collective to cushion the touch down. Like a few of the posters on this thread I use that technique most working days, I trust it, and practise rejects every six months. I never liked the S76 vertical due to the application of full power when on the ground, the loss of site picture and aggressive reject.

Give me what Eric did every time. The back up technique also guarantees obstacle clearance in the event of an engine failure after TDP.

And for those who doubt a goose could down a helicopter, how about the Blackhawk in January 2014 in Cley, Norfolk, UK, But I really don't believe either geeese, mute swans or anything else at the moment.

SND

[JimL]

Posted on another thread but probably best here.

Engines should meet a reliability figure of 1 x 10**-5; in ICAO parlance, this qualifies them as very reliable (the reason for the low standard is that a failure, at worst, should only result in an outcome of 'Major' - i.e. 'physical distress including injuries).

Tail-rotors should meet a reliability figure of 1 x 10**-9 because a failure could result in an outcome of 'Hazardous' or 'Catastrophic' - i.e. a fatality or multiple fatalities.

Reliability targets for tail-rotors are therefore 4 orders of magnitude better than engines - i.e. 10,000.

(A probability does not mean that a failure will occur after the reliability number has been reached, it can occur at any time but it should only occur once in the period.)

A helicopter certificated in Category A can depart or arrive utilising Category A procedures where failure of an engine should not result in damage.

A single-engine helicopter can depart or arrive using a Category B procedure where failure of the engine should not result in damage. It does this by accelerating below the HV avoid curve until it achieves a climb speed clear of the 'knee' of the HV curve.

Any departure other than that published in the Flight Manual - for either a Category A or Category B helicopter - could, following an engine-failure, result in a 'Hazardous' or 'Catastrophic' outcome (with a probability for a single of 1 x 10**-5, or for a twin or 2 x 10**-5).

An engine-failure in the cruise for a twin will be a non-event. An engine-failure in the cruise for a single might result in an outcome of 'Major' (as above) unless it is being flown over a hostile environment in which case the outcome might be 'Hazardous' or 'Catastrophic'.

In the recent accident, the profile flown was the AW169 Category A variable TDP procedure. Whatever caused the accident was not the result of having flown this procedure. It was within the defined and certified operational envelope.

JimL

[Buster15]

With the scant information available to the public at this point....Commonsense alone indicates considering all possible causes to be the bett4er course.

Watching video's taken from several perspectives does tend to point one's interest in one direction but absent more definitive information pointing a finger at a cause at this time is pure speculation.

Absolutely right. I have been involved in a number of accident investigations and on more than one occasion was pressurised to identify/speculate on the cause before before even starting the investigation.

The maxim is keep your mouth shut and your eyes wide open and let the investigation unravel the cause and effect.
This is particularly important when there is loss of life.

[Torquetalk]

a reduction in collective to contain the power (not slamming it down)

Is max power not limited by automatic switching to an OEI mode as with the 139? Lowing the collective in a 139 reject is to check the climb and intiate descent, and need not be (often should not be) a big reduction.

I never liked the S76 vertical due to the application of full power when on the ground, the loss of site picture and aggressive reject.

Roger that. S76 legacy habits applied to a light 139 rig departure using max available power are quite a ride. Hard to disaude the hard-wired or TDP concept averse.

And for those who doubt a goose could down a helicopter, how about the Blackhawk in January 2014 in Cley, Norfolk, UK, But I really don't believe either geeese, mute swans or anything else at the moment.

S76 also lost to birds in the US a few years back. But also sceptical in this case.

[Torquetalk]

Zero Airspeed Auto with pedal turns.....normal part of every CoA Airtest on Bell 212's for sure SASless

UK CAA Certificate of Airwothiness Test Flight Requirement.

The CAA had some interesting requirements for the CoA.


You live and learn.

[Sir Niall Dementia]

[QUOTE=Torquetalk;10301362]Is max power not limited by automatic switching to an OEI mode as with the 139? Lowing the collective in a 139 reject is to check the climb and intiate descent, and need not be (often should not be) a big reduction.

I don't know on the 169, I've only got as far as looking at it for a prospective purchaser, but the reject should only need a check down. I don't know how the 169 protections work, but what you state is logical. I do think that the thinking from the colonies is that a Class 1back-up is either complex or tough on the aircraft. It just isn't. In fact the easiest part of it is that apart from a look to make sure you're inside SSE, and the thing isn't on fire, the whole reject is flown on the edge of the translational burble, giving fantastic references for speed being right, allowing eyes out to touch down, and that is the same on every aircraft I've flown with such a profile apart from the S76.

SND

[Gustosomerset]

Whatever caused the accident was not the result of having flown this procedure. It was within the defined and certified operational envelope.
JimL

I completely understand that the procedure was 'within the defined and certified operational envelope' - my question was whether or not it was 'normal' in terms of how others had observed this and similar aircraft taking off from this location in similar circumstances before. Equally, I didn't mean to suggest that - even if the procedure was 'abnormal' in those terms, it was the cause of the accident.
I was really wondering if there could have been a perceived anomaly in the performance/response or any other aspect of the aircraft (that we can't see) that might have lead to the pilot wanting to gain more height that 'normal' and that, if so, whether this might give any clues as to what subsequently caused the apparent catastrophic failure (that we can see).

[RVDT]

Zero Airspeed Auto with pedal turns.....normal part of every CoA Airtest on Bell 212's for sure SASless

UK CAA Certificate of Airwothiness Test Flight Requirement.

The CAA had some interesting requirements for the CoA.

I reckon that harks back to the days of 12E Hillers - you could rig them one way or the other - enough left pedal or right pedal but not both.

[RVDT]

I completely understand that the procedure was 'within the defined and certified operational envelope' - my question was whether or not it was 'normal' in terms of how others had observed this and similar aircraft taking off from this location in similar circumstances before. Equally, I didn't mean to suggest that - even if the procedure was 'abnormal' in those terms, it was the cause of the accident.
I was really wondering if there could have been a perceived anomaly in the performance/response or any other aspect of the aircraft (that we can't see) that might have lead to the pilot wanting to gain more height that 'normal' and that, if so, whether this might give any clues as to what subsequently caused the apparent catastrophic failure (that we can see).

The only 169 profile suitable to this stadium which factors obstacle clearance is the variable TDP helipad. The TDP is 115ft + the height of the obstacle in your takeoff path so I’d guess a minimum of 250-300ft. The single engine failure before TDP is a not an overly ‘dynamic’ manoeuvre unlike some types. You need good references through the chin window and you fly back down the same path with up to 192% TQ available.

TDP - is just that, a "decision point", before it you come back down after it you can fly away and achieve the MINIMUM clearance to obstacles. If you continue climbing about the only thing that changes is the obstacle clearance gets larger.

So what?

[[email protected]]

Countless times trying to get out of a tight spot in the boonies, back it up as far as you can go, get some airspeed whilst still in ground effect and then zoom climb it out at best angle. Many of those you'd never get out vertically, you just run out of puff before finding clear air above the trees. seen this technique advocated by the Aussie mil but it leaves you very poorly placed in the event of an engine failure since you are travelling too fast to stop before you rotate and have nowhere to go once you have rotated

[jimjim1]

There are 100 foot towers with cables to the north and east of the stadium. the stadium is in blue, centre background.
Would this influence departure planning?

According to Google Earth's radar the stadium flat roof is 19m above the pitch.

https://goo.gl/maps/ZLNQyosngDu

https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/1398x654/leicester_pylons_41a7a5fc083ff942790d4ec8487934ab70f8dfcc.pn g

Leicester City Football ground - in blue.

[Flying Bull]

Tc


I'm questioning it because it didn't work very well here did it? Cat A PC1 is so focused on one of two engines failing it completely disregards the extra exposure to the one and only tail rotor.

check post 562, engines fail more often than tailrotors.
And I ˋm not talking engine chips, had actually parts of the compressor going through the engine, a friend a loose generator smashing the engine bay, but no tailrotor related issues so far....

[KarlADrage]

And for those who doubt a goose could down a helicopter, how about the Blackhawk in January 2014 in Cley, Norfolk, UK, But I really don't believe either geeese, mute swans or anything else at the moment.

SND
Not sure I get the significance of this reference to this case. The Pave Hawk crash was caused by flying into a flock of geese, "at least three of which penetrated the cockpit glazing, and which rendered the flight deck crew unconscious".

[Washeduprotorgypsy]

I can't decide whether it's the alien insects, white swans, black swans, ghosted black trash bags, capitalist friendly communist saboteurs, monkey wrenching ghosts escaping the tailpipe right before our very eyes. Or if it's just plain old 'built on a Friday afternoon' to the irresistible call of the 'dolce vita' that is the root cause of this unfortunate event.

I know the 'old hands' here, know the hopelessness of the situation but I would like to address those with 'Walter Mitty' ideas of an ideal outcome to the scenario. Seeing as the manufacturers with their relatively bottomless time and intellectual resources haven't been able to accurately model yaw rate outcomes in the simulator. I wouldn't fault this fellow for overestimating his keel surface area while in the midst of a mortal split second decision in which the other option (while yaw free) looks like the drop of doom.

It's a classic crew room argument regarding autorotation deep within the vertical part of the HV curve, you have your nose diver/lawn dart school versus your saner and more conservative,keep the disc mostly level , 'bottom and pull ' school. The nose divers reassure themselves of their superiority by getting away with preplanned and pre rehearsed practice autos in the shady portions of the curve. It's a high risk gamble that doesn't allow time for any necessary thought or hesitation when the real thing happens. Much helped with a significant headwind and a field free of obstructions. I am going to cast this option out as pure 'holeshot' fantasy. ROD building to free fall speeds with insufficient height and airspeed to carve a proper flare trajectory..= lawn dart. Though Walter Mitty would have the panache to plant it across 'the away teams' goal line. Leaving us with the 'parachute' option.

It's an oft repeated statement in rotorcraft engineering textbooks that steady state vertical autorotation rates are very close to, if not a little greater, than what a parachute with an effective diameter equal to that of the rotor disc would yield. Knowing this we can build an idea of what the ideal 'bottom and pull' reaction is going to look like.

You can spare yourself the freshman physics headache by using the modern miracle of the internet, to enlist the help of a physics engine to calculate free fall with air resistance. https://www.omnicalculator.com/physics/free-fall-air-resistance. Go to advanced settings, set your coefficient of drag to 1(flat plat area) ,enter disc area and approx weight, height,air density is obtained within the sites database itself. Lock those parameters in. I've got that AW169 coming to pitch pull height with round about 55 mph of vertical velocity. (Equal to the cab dropped free fall by a crane at 100 feet) Sure the pitch pull might scrub 5 even 10 mph off, it's somewhat of a bone of contention. The real studious among us will figure this out by the height at which hover chop exercises can arrest the descent rate to zero.

It's nothing but ugly......but may encourage respect for the curve...or a change of profession. Paratroopers eat your heart out, Robinson drivers don't subtract anything for the pitch pull....

I don't pretend aspiring billionaires are safe in anything flown at this profile but would offer a shameless plug for a restricted weight ,modernized 212 or 214st. Beautiful Americana. Leave the martinis till the after party. Laughable as VIP ships but likely still the most favourable autorotation index of anything out there "off the shelf"

[SASless]

Washed, Very Well said!:D


Karl,

The S-76 was at cruise speed when it collided with a large Red Tailed Hawk which shoved the Engine Lever Quadrant rearwards after shoving the Windscreen upper frame rearwards.

[jumpseater]

And for those who doubt a goose could down a helicopter, how about the Blackhawk in January 2014 in Cley, Norfolk, UK, But I really don't believe either geeese, mute swans or anything else at the moment.
SND
Re Birdstrikes a good few years back I did some extensive studies and stats analysis on bird strikes for a FW commercial airline.
Most strikes high 90%'s occurred in daylight/twilight hours, night strikes were very rare.
If I recall the numbers correctly, most impacts likely 2/3rds were beneath 3-400ft height.
I can't recall any reports of a strike that wasn't some form of head on collision, be it airframe/nose/screen/leading edges, engines and ingestions into engines.

Assuming a direct tail rotor strike, I'd be very surprised if a bird (singular) faced with a relatively slowly manoeuvring helicopter in its path, anticols flashing, high noise and downdrafts etc didn't take its own avoiding action, i.e turn away from the helicopter, as most species do react negatively to various forms of pyrotechnics and noise.
I'd anticipate a hovering, or slow moving helicopter to be producing enough downward turbulence and rotor wash to potentially protect it from a bird strike?

[gulliBell]

...offer a shameless plug for a restricted weight ,modernized 212 or 214st. Beautiful Americana...


Beautiful indeed, and sounds even more beautifuller.

[SASless]

A Billionaire VIP Helicopter.....a Bell 212?

Only if the Boss Fellah likes his Martini shaken and not stirred!

[John Eacott]

Re Birdstrikes a good few years back I did some extensive studies and stats analysis on bird strikes for a FW commercial airline.
Most strikes high 90%'s occurred in daylight/twilight hours, night strikes were very rare.
If I recall the numbers correctly, most impacts likely 2/3rds were beneath 3-400ft height.
I can't recall any reports of a strike that wasn't some form of head on collision, be it airframe/nose/screen/leading edges, engines and ingestions into engines.

Assuming a direct tail rotor strike, I'd be very surprised if a bird (singular) faced with a relatively slowly manoeuvring helicopter in its path, anticols flashing, high noise and downdrafts etc didn't take its own avoiding action, i.e turn away from the helicopter, as most species do react negatively to various forms of pyrotechnics and noise.
I'd anticipate a hovering, or slow moving helicopter to be producing enough downward turbulence and rotor wash to potentially protect it from a bird strike?


Unfortunately birds don't read Rotorheads and the tales of birdstrikes in just those conditions are legion. Mine include an albatross flying into the main rotor of a Sea King running on deck, Spot 5, HMS Ark Royal, ready for takeoff with the ship steaming at 15kts. Another was hover taxiing out in a 412 at an airport, and so on.


The premise in this accident has a likelihood somewhere between nil and -10, as the remains would easily have been visible on the TR blade(s) and identified early in the investigation. Returning to discuss a birdstrike on the TR is just wasting bandwidth, IMO.

[SASless]

Brother Eacott has made a statement of fact that I fully endorse.


Returning to discuss a birdstrike on the TR is just wasting bandwidth, IMO.


Let's move on to yet another silly notion shall we?

[DOUBLE BOGEY]

SAS I agree 99%. I leave 1% open in case AAIB find twas a bird that did it!

[604driver]

FW Pilot here.

Perhaps the the type of departure chosen was precisely because there was a good chance it would be filmed being as they were departing the scene of a Premiership footy match. I think if the eyes of the world were on you, you would conform with the procedures in the book to prevent a polite request to come to Gatwick and explain why you didn’t do it by the book, should that type of footage become available to the chaps down there.

That might explain why one option was chosen as opposed to another? Not sure.

I’ve learnt a lot reading this thread. Thanks for education. Apologies for chipping in if the above is irrelevant.

[SASless]

I have lost track of all the fanciful notions that have been put forth.....not withstanding the amount of video available for viewing that should be a decent starting point for discussion.

Of late....it has been like playing Cricket in a Corn field....it is very hard to keep one's eyes on the Ball.

[DOUBLE BOGEY]

604 Driver, for the most part, professional helicopter pilots follow the rules and procedures. Regardless of who's watching or otherwise. The departure flown looked to me like the optimum solution for obstacle environment he was operating in. Although it would seem very strange to a fixed wing man or even a SEH pilot, moving upwards and backwards has been a feature of VTOL Helipad Profiles in almost all modern MEHs. I did not know the pilot but friends have posted here and he would seem a very competent careful man. Majority of professional helicopter pilots posting here will agree that when faced with such a departure, an extra level of care is taken to try an fly the profile accurately. Mostly because we are always exposed to these profiles in the FSTD with OEI events. The video certainly supports a very careful, well flown departure until whatever happened in the latter stages of the initial climb.

[604driver]

Thanks DB.

I should have mentioned Towering Departure Viz a Vis the back up as opposed to not following regs 👍 but thanks for taking the time there.

Eric was regarded very highly in the FW world. I’m sure that’s the case in the RW too.

[aegir]

It seems the Aw169 was grounded by Leonardo due to "tail rotor shaft problem".
Anyone can confirm this rumor?

[Nadar]

It seems the Aw169 was grounded by Leonardo due to "tail rotor shaft problem".
Anyone can confirm this rumor?

Could this (https://www.cornwalllive.com/news/cornwall-news/isles-scilly-helicopter-grounded-after-2166254) be the source of the rumor?

[aegir]

No my rumors came from EMS world.

[KarlADrage]

It seems the Aw169 was grounded by Leonardo due to "tail rotor shaft problem".
Anyone can confirm this rumor?
It's not fleet-wide if there is one. There are examples currently showing up on FR24.

[EESDL]

It would appear from reading the local paper that ISSC were looking for a reason to take their scheduled service offline......

[fairflyer]

It's not fleet-wide if there is one. There are examples currently showing up on FR24.

No ADs on type since September:

https://cimg4.ibsrv.net/gimg/pprune.org-vbulletin/1398x585/ads_80968a84a91dd45777698be30bbacb391bd6f936.jpg

[bumpthump]

Non pilot question. I (think) I understand the need for the yaw to port so the pilot can keep line of sight with his departure point.
Once he yaws back to starboard and loses sight of his departure point, is this part of the TDP (ie, he is now committed to generating some airspeed), and at this point when he yaws round to his intended departure route, has he ceased climbing?

Hope you guys are ok with layman questions of this nature.

[griffothefog]

Back in the day, we would have taxied down to one goal and charged at the other with a zoom climb...
the BO105 had zero performance and a strange reliance with Allison engines 😱😱

[chopjock]

Back in the day, we would have taxied down to one goal and charged at the other with a zoom climb...
the BO105 had zero performance and a strange reliance with Allison engines 😱😱
If you went diagonal corner to corner you would have an extra 20m or so...

[Overdrive]

"If you went diagonal corner to corner you would have an extra 20m or so..."


...and at some grounds, a nice gap in the corner between the stands.

[Flying Palm Tree]

Two innocent questions from a bystander:
1. For how long can you remain static beating a hole in the air before it becomes a problem?
2. Is it possible for mechanical failure other than TR drive failure to cause a spin? That's to say pedal linkage failure for example?

[Art of flight]

Two innocent questions from a bystander:
1. For how long can you remain static beating a hole in the air before it becomes a problem?
2. Is it possible for mechanical failure other than TR drive failure to cause a spin? That's to say pedal linkage failure for example?
1. Police helicopters spend a great deal of time in very high OGE hovers without problems, day and night.
2. Yes.

[ShyTorque]

Non pilot question. I (think) I understand the need for the yaw to port so the pilot can keep line of sight with his departure point.
Once he yaws back to starboard and loses sight of his departure point, is this part of the TDP (ie, he is now committed to generating some airspeed), and at this point when he yaws round to his intended departure route, has he ceased climbing?

Hope you guys are ok with layman questions of this nature.

Bumpthump, During a Class 1 departure, the pilot doesn't "yaw round to his intended departure route". The aircraft is flown straight ahead until the second phase of the departure profile is completed, which involves lowering the nose, gaining some forward airspeed then climbing ahead. The aircraft is then turned in balanced flight in the climb onto the desired heading.

[SASless]

Back in the day, we would have taxied down to one goal and charged at the other with a zoom climb...
the BO105 had zero performance and a strange reliance with Allison engines ����

Heresy....Heresy.....how dare you mention such a thing!

[Misformonkey]

Two innocent questions from a bystander:
1. For how long can you remain static beating a hole in the air before it becomes a problem?
2. Is it possible for mechanical failure other than TR drive failure to cause a spin? That's to say pedal linkage failure for example?
Engines are rated to provide different power settings over prescribed time intervals. An example being 1 hour power and another being Max Continuous.
Yes. T/R cables can fail causing a predefined pitch to be introduced allowing a degree of control rather than a hard over control.

[gulliBell]

Heresy....Heresy.....how dare you mention such a thing!

He said it...I was just thinking it.

[gulliBell]

Two innocent questions from a bystander:
2. Is it possible for mechanical failure other than TR drive failure to cause a spin? That's to say pedal linkage failure for example?

TR control malfunctions never cause loss of control of the helicopter. Not to the extent we saw in the video.

[SASless]

I was a very bad influence upon young Griffo!

I shall accept some blame for his lapse......not a lot but some!

[simfly]

I believe a service bulletin emergency alert has just been issued by Leonardo. Assuming what I just received is legit, inspections to the back area of the TR servo-actuator required to be carried out within next 5 flying hours or one day, whichever sooner, following an in service event. "Incorrect installation may lead to loss of TR control".

[simfly]

TR control malfunctions never cause loss of control of the helicopter. Not to the extent we saw in the video.
I think that's incorrect. The S92 incident at the Franklin platform was loss of tail rotor control due to servo issue?

[bumpthump]

Bumpthump, During a Class 1 departure, the pilot doesn't "yaw round to his intended departure route". The aircraft is flown straight ahead until the second phase of the departure profile is completed, which involves lowering the nose, gaining some forward airspeed then climbing ahead. The aircraft is then turned in balanced flight in the climb onto the desired heading.
Thanks for the explanation. That makes perfect sense,and aligns with my years of N Sea passenger experience,...although I have never been involved in that kind of take off personally.
That being the case, was there an operational reason for the (controlled?) yaw to starboard immediately prior to the incident?

Apologies again if the questions appear inane. In no way am I trying to “solve the mystery” in my own head. Having been a passenger in commercial helicopters for 40 years, the insights here are an education in themselves, and help me to gain some understanding of what was a significant part of my life for so long.

[atakacs]

I believe a service bulletin emergency alert has just been issued by Leonardo. Assuming what I just received is legit, inspections to the back area of the TR servo-actuator required to be carried out within next 5 flying hours or one day, whichever sooner, following an in service event. "Incorrect installation may lead to loss of TR control".
Haven't seen it (yet?). Last I have on record dates Oct 22nd.
Anyone else!?

[[email protected]]

Bumpthump - at TDP, if using the AW confined area profile, the yaw offset to provide sight of the LS is taken out as the nose is pushed forwards to gain speed. thereafter it is as Shytorque says

[vaibronco]

Non pilot question. I (think) I understand the need for the yaw to port so the pilot can keep line of sight with his departure point.
Once he yaws back to starboard and loses sight of his departure point, is this part of the TDP (ie, he is now committed to generating some airspeed), and at this point when he yaws round to his intended departure route, has he ceased climbing?

Hope you guys are ok with layman questions of this nature.
the yaw to keep the point in sight is in the 139 confined procedure
in the 169 variable tdp procedure you keep the point in sight between your pedals

[silverelise]

TR control malfunctions never cause loss of control of the helicopter. Not to the extent we saw in the video.
These two sentences contradict each other. :confused:

[Aucky]

Bumpthump - at TDP, if using the AW confined area profile, the yaw offset to provide sight of the LS is taken out as the nose is pushed forwards to gain speed. thereafter it is as Shytorque says

In the instance of the 169 variable TDP procedure it’s not necessary because flown correctly you should have the pad (and reject area) in full view between the pedals through the chin window all the way up to TDP. You aren’t needing a good visual picture of what is hidden by the instrument panel. Offsetting could actually lead to a condition where you have the wrong sight picture through the pedals. There is nothing in the video to suggest he did offset the nose left during the initial manoeuvre - it’s looks perfectly straight.

AW169 QRH - The G&E H/H variable TDP consists of a slow (less than 300 fpm) climb above the take off surface maintaining the centre of the take off surface in sight between the yaw pedals up to TDP. The pilot then rotates to transition to forward flight and into the climb

[pm07a2m]

In the mean time lhd has issued a mandatory alert sb on the whole 169 fleet. An ispection on TR flight control

[toptobottom]

Which maintenance organisation would have been looking after this helicopter?
Sloane, I believe.

[gulliBell]

These two sentences contradict each other. :confused:

No they don't. TR control malfunction you should still be able to land the helicopter at a place of your own choice, without any particular urgency, and without putting a scratch on the aircraft. TR drive malfunction is far more serious, with far less options available, which can very quickly lead to loss of control.

[212man]

No they don't. TR control malfunction you should still be able to land the helicopter at a place of your own choice, without any particular urgency, and without putting a scratch on the aircraft. TR drive malfunction is far more serious, with far less options available, which can very quickly lead to loss of control.

I would tend to disagree. A TR Servo problem could include an uncommanded full input in either direction, which is the equivalent of applying full yaw pedal - which is very much like what we see in this incident. I fail to see how that can be considered 'controllable'. The S92 referred to earlier may have had a similar outcome if not a few feet above the deck.

[Sandy Toad]

This is now applicable to AW189 Fleet too.
I understand this would not normally be disturbed during maintenance.

[DOUBLE BOGEY]

Gullibell - sorry bud but you are missing an important point. TR Control Malfunction leading to a minimum power hard over is almost the same as Drive Failure and will force an EOL in most types of helicopters. Obviously most types with duplex hydraulics have design features to try to avoid hardovers, but if an input lever detaches...….blades throw off pitch...…..bye bye anti-torque thrust!

[oldbeefer]

"s it me or is that wire locking incorrect in the pic above?"

I don't think so - looks as though the smaller bit on the end is part of the shaft and the big nut covered in blue is locked to it.

[hoodie]

Is it certain that the "in service event" referred to in the SB is the Leicester accident?

[212man]

Is it certain that the "in service event" referred to in the SB is the Leicester accident?
It seems hard to imagine otherwise.

For info, in the S92 incident referred to above by simfly and me, from the report it says: " it yawed rapidly to the right, reaching a maximum rate of 30° per second. " Bear in mind it was 4 ft above the deck and landed after only 146° of yaw, imagine how it would have developed from the same position that Eric found himself in!!

[212man]

This is now applicable to AW189 Fleet too.
I understand this would not normally be disturbed during maintenance.

Yes: 189-213

[nomorehelosforme]

https://www.bbc.com/news/uk-england-leicestershire-46107923

[SASless]

From the AAIB site:


https://www.gov.uk/government/news/update-on-leicester-helicopter-accident-g-vskp

[bumpthump]

Bumpthump - at TDP, if using the AW confined area profile, the yaw offset to provide sight of the LS is taken out as the nose is pushed forwards to gain speed. thereafter it is as Shytorque says
Thank you.

[GrayHorizonsHeli]

Trying to think of a way an installation maintenance error could be made here? The washer (140) on the wrong side of the bracket or incorrect wire locking so the nut isn't locked to the shaft?

My thoughts, and reading the wording of the inspection, makes me think that perhaps the safety wasn't there at all or failed, and the nut backed off completely. That of course would remove your pitch control completely

you would still have your T/R drive all the way thru this event, and that would explain the strike damage in the picture we debated earlier.

[SASless]

Is the Tail Rotor designed to go to neutral pitch or some position such as the BK is which uses counter weights?

[GrayHorizonsHeli]

I would think most TR's would find their neutral spot. No idea what this TR assembly would do.
I look at item 90 as a part that might affect that point should it get cockeyed or jammed somehow once everything got loose. Pin 80 must get pinch fitted somehow under torque of the nut to prevent it from coming out under normal circumstances

No idea how it is put together though, so I'm only guessing

[SASless]

Mitch....we are talking about a 169....not a 92.

My question was very much Type specific.

How the Tail Rotor would react if this component came adrift would determine how the aircraft reacted to the failure.

Would the Servo(s) go hard over in one direction or another....or would there just be a loss of Pilot input and the Tail Rotor itself be free to find some position it liked?

Perhaps some Engineers that work on the 169 can advise us on that?

[FlightSpanner]

Mitch....we are talking about a 169....not a 92.

My question was very much Type specific.

How the Tail Rotor would react if this component came adrift would determine how the aircraft reacted to the failure.

Would the Servo(s) go hard over in one direction or another....or would there just be a loss of Pilot input and the Tail Rotor itself be free to find some position it liked?

Perhaps some Engineers that work on the 169 can advise us on that?

The nut in question is on the end of the pitch change shaft, after the pilot input and servo assy, so neither of these would be able to transmit any movement to the TR pitch.

[SASless]

Thank You!

That is very helpful insight into the mechanism of how this thing might have failed.

What drove my question is the BK-117, for example, in the event of a loss of pilot input (linkage failure for example) the tail rotor has counter balance weights that are supposed to return the Tail Rotor to somewhat a neutral position rather than it being able to hunt for a position it likes which could cause severe handling issues.

I was curious if the 169 was similarly designed in some way.

[FlightSpanner]

Yes, item 110 would have flapped loose of the TR Pitch shaft which means the TR pitch shaft would have been stuck in its last commanded position with no way to counter it?
Could stick, go to a designed position or zero pitch, sorry don't know the answer

[DType]

General comment on servos:-
If the feedback fails then the servo will drive to the end stop.
Feedback is negative, it tells the servo when to stop.

[skadi]

True, neither do I. However, we have the video footage to go off so it's very likely that it was stuck in its last commanded position rather than returning to a central datum.

The result was like a TR failure, so no more thrust. That indicates, that the TR went in a kind of neutral position, not stucked in high power position.

skadi

[FlightSpanner]

The result was like a TR failure, so no more thrust. That indicates, that the TR went in a kind of neutral position, not stucked in high power position.

skadi
Have to agree, the acceleration in rotation to me indicates this possibility.

[FlightSpanner]

If the TR went into a neutral position, why did the rate of rotation speed up rather than slow down? There is no sign of a correction in the video, only a deterioration. The speed of rotation gains momentum which suggests (to me anyway) the yaw was fully extended with no way of it resetting/correcting. As it gained momentum it made the spin even more violent.

Are you suggesting drive to the tail rotor failed so the TR was no longer being driven or along the same lines of it being a control issue?

The TR was in a fairly high load, drive remained but the pitch decreased due to its neutral position. Hence the spin

[Nadar]

I think there are two different "neutral" concepts in play here now. Neutral can mean no TR blade pitch, which should be roughly the same as a TR drive failure, but neutral can also mean "provide enough torque to counter the torque from the main rotor".

I would think that if left to "adjust itself", the first kind of neutral would be most likely, while the second kind of neutral would be what one would want as a safety fallback for control failure.

[ShyTorque]

If a tail rotor control servo runs away to full negative pitch (some most definitely can do this and I’ve written about this before in previous threads) it will give a situation worse than a failed tail rotor driveshaft. The aircraft will continue to yaw away from the main rotor direction despite all main rotor torque being removed by fully lowering the collective and shutting down the engines. The pilot would be unable to correct this. A horrible situation.

[jellycopter]

Mitchaa wrote "The speed of rotation gains momentum which suggests (to me anyway) the yaw was fully extended with no way of it resetting/correcting. As it gained momentum it made the spin even more violent."

My speculation from experience of other designs; if the T/R control became disconnected, the blades would revert to a pre determined position by design. This position is a balance between aerodynamic and centrifugal turning moments which are usually designed to apply some positive pitch to the blades to allow a running landing. In a vertical climb OGE, this pitch setting would not be sufficient to prevent yaw developing (quite rapidly).

Now to address Mitchaa's observation of the rate of turn accelerating; as the yaw rate develops, the effective NR reduces, and more collective is required to maintain height, the torque reaction increases and yaw rate increases further, requiring increased collective pitch due to an even greater reduction in effective NR. It's a viscous circle. This would apply in the first few seconds before the descent was initiated. After descent is initiated, this theory falls down as the yaw rate would reduce noticeably and the video didn't really show this.

If the yaw servo did indeed travel to full deflection due to lack of feedback loop, then the rate of deflection, and consequent yaw, would be a function of how much the servo control valve was open at the time of failure. This could explain the relatively progressive increase in yaw rate initially.

If it was indeed a servo 'runaway', then deselection of the appropriate hydraulic channel should allow the blades to revert to the position mentioned above and permit some reduction in yaw rate and recovery of control.

I now refer you to a post I made https://www.pprune.org/showthread.php?p=10298782
There I tried to explain that tail rotors don't tend tofail 'quietly'. However, servo runaways are 'quiet' and should not be mis-diagnosed as a t/r drive failure, despite similar yaw rates.

JJ

[Barcli]

Trouble is JJ , the SB isnt really relevant to a servo runaway. Its relevant to a structural failure of the parts concerned or even more explicit of a missing split pin / nut/ wirelocking procedure. I hope they are also looking at security at Fairoaks.

[Echo Romeo]

So, what maintenance procedure would necessitate the removal or loosening of that nut? Excepting the replacement of another component such as the servo.

[Cows getting bigger]

Thoughts? A $2 nut (or thereabouts before being associated with an EASA Form 1), mitigated by a piece of locking wire, presents the potential of a catastrophic single point of failure.

[FlightSpanner]

Thoughts? A $2 nut (or thereabouts before being associated with an EASA Form 1), mitigated by a piece of locking wire, presents the potential of a catastrophic single point of failure.

unfortunately yes, although it is split pinned and wire locked!

This is the case for many components, hence two locking methods, duplicate inspections and daily visuals.

[noooby]

Thoughts? A $2 nut (or thereabouts before being associated with an EASA Form 1), mitigated by a piece of locking wire, presents the potential of a catastrophic single point of failure.

You are aware that helicopters are littered with single point failures aren't you.

Any MR Servo Mount bolt. Any MR Blade Bolt. Any TR Blade Bolt. The "Jesus" nut, to name but a few. There are certification limits for the probability of failure of these critical items, which has been mentioned here already.

This nut is double locked. A dirty fat Split/Cotter Pin and lockwire. No single locking method failure should induce a failure of the control. Both locking systems have to fail. And with the nut being upstream of the servo assist it does not have flight loads on it only the same loading that the pilot feels on his/her feet.

This "nut on the end of the servo" system has flown for years and years on the 139 and 189. Although the 139 nut is slightly different. The 189 also has an SB out for inspection of the nut (out this morning).

I anxiously await the next update from the AAIB.

[MurphyWasRight]

Trouble is JJ , the SB isnt really relevant to a servo runaway. Its relevant to a structural failure of the parts concerned or even more explicit of a missing split pin / nut/ wirelocking procedure
Not clear that this is true, looking at the SB wording and diagram only (and with no knowledge of the system) it refers to the 'Servo feedback link". If it is indeed inside the control loop disconnecting it could very much result in a servo runaway. That said it would also seem to be a critical path and might well have a redundant path of some sort beyond what is shown.
Hopefully someone with knowledge of the system can comment on this.

[noooby]

Not clear that this is true, looking at the SB wording and diagram only (and with no knowledge of the system) it refers to the 'Servo feedback link". If it is indeed inside the control loop disconnecting it could very much result in a servo runaway. That said it would also seem to be a critical path and might well have a redundant path of some sort beyond what is shown.
Hopefully someone with knowledge of the system can comment on this.

The lever has three attachment points. The far end is where the control rod from the pedals connects. In the middle is the linkage that operates the pilot valve that then moves the servo. The end that is being inspected is connected to the servo itself. When this moves it resets the pilot valve to stop servo movement.

Standard method of controlling servos.

[MurphyWasRight]

The lever has three attachment points. The far end is where the control rod from the pedals connects. In the middle is the linkage that operates the pilot valve that then moves the servo. The end that is being inspected is connected to the servo itself. When this moves it resets the pilot valve to stop servo movement.

Standard method of controlling servos.
Thanks, that is roughly what I guessed from the diagram, works by balancing the control input and servo output to a "zero'' at the pilot valve, in electronics same as an op-amp.

So Is this roughly correct?
If the control path disconnects the system could be rigged to settle on the 'aerodynamic neutral' mentioned above.
If the feedback path fails then the servo will likely continue to be driven to a stop since there is no (or at least incorrect) input at the pilot valve.

[Overdrive]

"3.2 Check the connection elements of the input lever (110) of the TR servo-actuator
taking particular care on the lever feedback link."


Was that photograph issued with the SB? If so, was there another photo? The position referred to in the above text is not shown, the way I'm interpreting (or trying to). Also, should the word after "(110)" be to the servo-actuator, not of? They also call component #110 both "Input lever" and "Lever feedback link". I'm thinking the intention of SB item 3.2 is to order a check of the connection to the servo from part 110, which can't be seen in the posted photo.

[Cows getting bigger]

You are aware that helicopters are littered with single point failures aren't you.



Silly old me, I thought we were in the business of reducing/mitigating risk and not just accepting the status quo. Is a split pin and a locking wire really the best way? Clearly someone has recognised the importance of this nut. Perhaps the whole linkage could be redesigned.

[Overdrive]

At some point, Mr. Cows, an assembly or artefact has to terminate. There are only so many ways to connect things together in a manner that can be dissembled and rebuilt. There is also only so much material and weight that can be used and included too. I think all methods have been tried by now!

If a split pin and a lockwired nut on an assembly of high quality design and material fail, on the back of proper maintenance and inspection, then one really is subject to the worst of probability.

[Overdrive]

Mitchaa - thanks.

[MurphyWasRight]

I would think it would be nigh on impossible to have a failure of the pin and the wire locking considering as someone else has mentioned, there’s no loading there, they are simply to lock the nut to the shaft.

The release of the SB most probably points to neither the pin or the locking wire being present. The big question, were they ever fitted and locked and if so, how did 2 sets of eyes during a duplicate inspection miss it? Not impossible, but certainly unusual.
It is also possible that the SB resulted from an observation of condition of the recovered assembly. By itself does not 'prove' that this is the cause of the accident.
In other words they saw something unexpected that warranted inspections such as incorrect assembly order but not by itself the root cause.
Would a hard over servo runaway result in the reported (by some only) grinding noises?

[Sky Sports]

It is also possible that the SB resulted from an observation of condition of the recovered assembly. By itself does not 'prove' that this is the cause of the accident.
In other words they saw something unexpected that warranted inspections such as incorrect assembly order but not by itself the root cause.

It is also a possibility that the SB resulted from an observation on an aircraft on the other side of the world. Quite often, maintenance engineers, when they get a sense or a hunch of what caused an accident, will in the following days, take a stroll over to a similar machine in the hangar and just take another good look at the suspect system. Its sometimes at that point that things like anti-locking on components - that have been there since manufacture - suddenly become apparent.

[Tony Mabelis]

Trouble is JJ , the SB isnt really relevant to a servo runaway. Its relevant to a structural failure of the parts concerned or even more explicit of a missing split pin / nut/ wirelocking procedure. I hope they are also looking at security at Fairoaks.

'The security at Fairoaks'.................... as a retired LAE, I am wondering about the possibility of sabotage, locking pins and wire locking do not fail simultaneously.
Tony

[Barcli]

I have never even met a billionaire but I have worked for several millionaires. They had some nasty enemies - they didnt become millionaires by being nice in business. I know nothing of Thai politics.

[ShyTorque]

Jellycopter,

My speculation from experience of other designs; if the T/R control became disconnected, the blades would revert to a pre determined position by design. This position is a balance between aerodynamic and centrifugal turning moments which are usually designed to apply some positive pitch to the blades to allow a running landing. In a vertical climb OGE, this pitch setting would not be sufficient to prevent yaw developing (quite rapidly).

That might be true for smaller helicopters but if there is a flying control hydraulic system driving the tail rotor servo to either full positive or full negative pitch, that can't possibly happen. Some aircraft do have a centreing device to hold the servo at a pre-set mid range pitch position if the flying control run disconnects (e.g. control cable break), others don't. In a situation where the control mechanism fails, any number of things might happen. If the servo puts the tail rotor pitch to a medium or neutral position, you might be able to control the aircraft in yaw by either varying the main rotor torque, by changing the airspeed, or a combination of both. If the tail rotor pitch ends up at either full positive (anti-torque) pitch, or as possibly happened in this case, somewhere near maximum negative (pro-torque) position, you are in a very dire situation indeed. The fixed wing equivalent would be a rudder hard over and an engine failure on the same side that the rudder surface had moved to.

To put some typical figures on this, an aircraft you might remember very well (Puma) has a tail rotor pitch range of something like +35 degrees to -17 degrees astride the "zero pitch" datum. The RAF HC1 had no tail rotor pitch centreing device fitted, whereas the civilian Super Pumas did.

[sycamore]

Are all these components covered by a cowling/in the fin ,or exposed,on view....?

[EGPI10BR]

Well no, quite. Which is really my point. However incredible the proposed method, there's probably someone mad enough to believe it's a clever idea...

Got you. Indeed. If a potential assassin had gained access to the aircraft, then there would be better methods of securing a successful outcome for them.

[EGPI10BR]

If you wanted to bring down a 169 and it’s billionaire owner and make it look like an accident then this would be the perfect way to do it. Not glaringly obvious and not an instant failure.


Quite. There is no guarantee that the target was in the aircraft when the nut falls off. I’m sure that the people down in Farnborough will get to the cause soon enough and involve the relevant authorities of foul play is a possibility.

Misty.

[noooby]

Are all these components covered by a cowling/in the fin ,or exposed,on view....?

Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

For those reading the SB and thinking this is directly related to this incident, it is not. AAIB have not given Leonardo any information that leads Leonardo to believe this to be the cause of the crash. Leonardo are being proactive. That is what Leonardo Customer Support are advising 169 owners.

Has Leonardo looked at the videos? You bet. Have they looked at all the possible mechanical issues that may cause this? You bet. And this would seem to be the most likely scenario that they have come up with on their own.

Doesn't mean it is the actual cause of this accident though.

[noooby]

Silly old me, I thought we were in the business of reducing/mitigating risk and not just accepting the status quo. Is a split pin and a locking wire really the best way? Clearly someone has recognised the importance of this nut. Perhaps the whole linkage could be redesigned.

What do you think holds on the complete main rotor on a Jetranger? One big nut (not self locking) and two pieces of lock wire. THAT IS IT. And the fact that the nut is effing tight.

So how, pray tell, would you redesign it? Make the whole helicopter one piece???? There are only three methods that are easily used to lock a nut. Lockwire, split pin and tab washer. For critical components you should use two of the three or repeat one twice. Although it you use a self locking nut you can legally get away with only one.

And go.......

[noooby]

Thanks, that is roughly what I guessed from the diagram, works by balancing the control input and servo output to a "zero'' at the pilot valve, in electronics same as an op-amp.

So Is this roughly correct?
If the control path disconnects the system could be rigged to settle on the 'aerodynamic neutral' mentioned above.
If the feedback path fails then the servo will likely continue to be driven to a stop since there is no (or at least incorrect) input at the pilot valve.

I believe you are correct though I'm not entirely sure about the 169 TR Servo. Often the servos are made so that the pilot valve is spring loaded (for want of a better term) to neutral. That doesn't mean the servo goes to neutral. It means the servo stops moving, wherever it may be at the time.

If the feedback path fails, as I see it on the diagrams, then there is nothing to tell the pilot valve to stop porting fluid to the servo. So it would, in theory at least, go full one way. What I don't know is if manipulation of the pedals could still operate (albeit very roughly) the pilot valve, thereby controlling the servo to a certain extent. You'd have to try that on a 169 with a hydraulic cart hooked up. I also don't know if the servo will self-center if the feedback loop is disconnected.

In other words, if the lever is no longer connected to the servo through the feedback attachment, is any self centering force on the pilot valve enough to overcome the weight of the lever? If yes, then the servo should stop where it is. If no, then it may be possible for it to keep on moving to full extension.

I do not however know the answer to that.

[sycamore]

Nooby,thanks for that.
Does the a/c have single or duplex hydraulics to the t/r servo, is it cable /pushrod actuated,and if duplex mains ,single system to t/r..ie could the t/r hyds be selected off...??..if you know..?

[helimutt]

Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

For those reading the SB and thinking this is directly related to this incident, it is not. AAIB have not given Leonardo any information that leads Leonardo to believe this to be the cause of the crash. Leonardo are being proactive. That is what Leonardo Customer Support are advising 169 owners.

Has Leonardo looked at the videos? You bet. Have they looked at all the possible mechanical issues that may cause this? You bet. And this would seem to be the most likely scenario that they have come up with on their own.

Doesn't mean it is the actual cause of this accident though.


Can you please link us to the actual 'in-service' event to which this sb applies? Odd that it does actually apply to an 'in-service' "event" so close to this accident. I, for one, can't say that I believe in coincidences of this nature. If you say Leonardo are being proactive, that doesn't imply that an Sb is released due to an in service event.

[What-ho Squiffy!]

I would tend to disagree. A TR Servo problem could include an uncommanded full input in either direction, which is the equivalent of applying full yaw pedal - which is very much like what we see in this incident. I fail to see how that can be considered 'controllable'. The S92 referred to earlier may have had a similar outcome if not a few feet above the deck.

Agree. It was obvious as a possibility from the beginning.

[What-ho Squiffy!]

Quite. There is no guarantee that the target was in the aircraft when the nut falls off. I’m sure that the people down in Farnborough will get to the cause soon enough and involve the relevant authorities of foul play is a possibility.

Misty.
Surely Occam's Razor suggests not, though. I'm no assassination expert, but there are plenty of ways to kill people in undetectable ways that also happily avoid killing lots of other people.

[What-ho Squiffy!]

I’ve heard a couple of people mention this today and just thought don’t be so ridiculous.

There was a billionaire on board, it wouldnt be hard to snip the lockwire, remove the pin and back the nut off. Those actions can be done in less than a minute if there’s access. It wouldn’t result in an instant failure but it would work it’s way loose over time. Too far fetched bordering on madness although anything is possible.


Wise words.

[GrayHorizonsHeli]

Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

For those reading the SB and thinking this is directly related to this incident, it is not. AAIB have not given Leonardo any information that leads Leonardo to believe this to be the cause of the crash. Leonardo are being proactive. That is what Leonardo Customer Support are advising 169 owners.

Has Leonardo looked at the videos? You bet. Have they looked at all the possible mechanical issues that may cause this? You bet. And this would seem to be the most likely scenario that they have come up with on their own.

Doesn't mean it is the actual cause of this accident though.


if you're part of AAIB or Leonardo, then their might be some weight to your claims...
Otherwise, I'm pretty sure Leonardo staff are working alongside AAIB staff and the information is flowing freely amongst them.

[MurphyWasRight]

Quote:
Originally Posted by noooby https://www.pprune.org/images/buttons/viewpost.gif (https://www.pprune.org/rotorheads/614822-helicopter-down-outside-leicester-city-football-club-not-condolences-post10303760.html#post10303760)
Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

For those reading the SB and thinking this is directly related to this incident, it is not. AAIB have not given Leonardo any information that leads Leonardo to believe this to be the cause of the crash. Leonardo are being proactive. That is what Leonardo Customer Support are advising 169 owners.

if you're part of AAIB or Leonardo, then their might be some weight to your claims...
Otherwise, I'm pretty sure Leonardo staff are working alongside AAIB staff and the information is flowing freely amongst them.

Nooby does not need to be part of AAIB or Leonardo, just needs access to what Leonardo tech support is saying about the SB. He is also not stating that there is not a flow of information, although I have heard unless it is an immediate safety action the flow can be mostly towards the investigators. (Added bold/italics in quote)

[Gustosomerset]

Looking at the diagram of how the pitch change shaft is locked to the feedback lever bracket, if the nut was missing something would have had to initiate the extension or retraction of the pitch change shaft for the feedback lever bracket to disconnect from the pitch change shaft. (Namely a commanded yaw action)
It never happened on the ground, nor in the climb. It looks to have happened as the pilot turns the aircraft to transition to forward flight.
Is there any significance to be drawn from the observation that the failure appeared to happen at the first point that the pilot commanded a yaw to the right (i.e. counter the MR rotation) as opposed to the slight yaw to the left observed (and explained earlier) during the climb?

[helimutt]

I’m led to believe, that this part isn’t something that would necessarily have been touched by the maintenance organisation since new. So unless work had been carried out on it for some other reason recently, it shouldn’t have needed touching. I’m certain the 145 op and aaib will be aware. This will be an interesting report no doubt. I have to say that I’ve read some absolute bo££ox on pprune accident threads but this one has it all. From Russian conspiracy theories to garbage expert witness statements to theorised pilot error and non existent SB which are SB, but not related to this event but related to a recent event. Wow.

[VintageEngineer]

To help the discussion on the pitch of the TR blades, I attach again a close-up of the TR at the crash site, plus the original it was taken from (as pdfs, I can't post images yet). The blades seem to be at a roughly neutral postion.

This may mean absolutely nothing, as, for example, the blades may be self-centred when hydraulic power is lost with or without the servo connected.

[silverelise]

Does anyone know the hours on the airframe? All I can see from a quick google is that it was delivered in August 2016. What are VIP aircraft doing per year? 2-300 hours? Likely hours to be around 5-600? (or more?)

The reason I ask, it may never have been disturbed by the Part 145 organisation? If the airframe is low hours, that particular part may never have been disturbed, fitted from factory and untouched? I guess it would still fall under calendar ops, 1 or 2 yearly inspection, but would that involve disconnecting that link? Perhaps they had an unscheduled removal which resulted in its disconnection? Again, only the Part 145 and AAIB will have the answers to that.

G-INFO reports registered in July 2016 and 283 total hours as at 28-Jun-2018 (not sure how reliable the G-INFO database is)

[Gustosomerset]

Only the extension/retraction of the pitch change shaft. It would appear once a full pedal input was made the feedback lever link disconnected itself from the pitch change shaft. It happened within 45 secs of take off and from the video, appeared to fail at the first significant yaw input. Was the nut in place before it lifted?

I understand. I think what I was getting at was whether pedal input in one direction (yaw left) might not be affected by the absence of the nut but that in the other direction (at the top of the climb for the first time) it would, as the absence of the nut would not affect a 'pushing input' but would allow the lever to pull itself away from shaft. If this were true, perhaps it could allow for the fact that control seemed normal in the climb - with no right yaw demanded - even if the nut was already on the ground. (Despite your excellent explanation of the mechanics I'm afraid I'm simply too stupid to fully understand).

As to this thread being full of "absolute bo££ox", IMHO I'd echo the point made earlier (which I can't now find) that for inexperienced pilots (such as me), the amount of insight from those who are far more knowledgeable has a value that far outweighs the obvious nonsense - which we can easily choose to skip.

[Mee3]

EC will also tell you that SBs for 225 and 365s are precaution. But we all know how did this board went about it.

[Art of flight]

[QUOTE=noooby;10303760]Completely covered. You need a ladder and a screwdriver and patience to get to the linkage.

I remember delivering a new EC135 T1 to a new owner, during a walk round of the aircraft with him he commented that the tail rotor seemed to be missing a fairing, I pointed out it never had one, to facilitate preflight inspection and daily maintenance. 2 years later I flew the new P2 version that did have a fairing covering the important bits. Being old school I'd rather be able to cast an eye and a torch over the Tail rotor components, the P2 looked tidier but I always thought it was an improvement that actually made things worse.

My only accident was a tail rotor drive failure, thankfully only from a high hover taxi, due to servicing error. The intermediate gearbox came off the tailboom with most of the drive shafts and tail fairings. I'd already completed 4 ground runs to track and vibe the Tail rotor which had had components replaced. The 5 bolts holding the shaft to the IGB had been replaced but the engineer had not replaced the nuts. The supervisor signed off the job and secured the fairings, from that point on the aircraft was doomed. I felt a slight vibe through the pedals for around 2 seconds before it went bang just as I moved forward after the post take off checks. Thankfully the non handling pilot got the ECLs back just as I got the collective down and we had rotated through a full 360 turn.

The missing nuts were still on the bench in the hangar, I've had a very wary approach to tail rotors ever since, particularly when they've been tinkered with!

[SASless]

Art....‘‘twas not the tail rotor that let you down!

[Art of flight]

Art....‘‘twas not the tail rotor that let you down!
very true SAS!

[noooby]

Nooby,thanks for that.
Does the a/c have single or duplex hydraulics to the t/r servo, is it cable /pushrod actuated,and if duplex mains ,single system to t/r..ie could the t/r hyds be selected off...??..if you know..?

First off, I'm just relaying what Leonardo is telling the operators when they ask about this SB. That the AAIB have not (as yet) given them any info about possible or probable causes of this accident.

Sycamore, the TR is duplex hydraulic. It is controlled with a single push-pull cable. Unlike previous Leo machines that have relied on control tubes. Hydraulics cannot be selected off as the aircraft cannot be flown without hydraulics.

I know as much as any 169 operator who asks the right questions :)

[MurphyWasRight]

First off, I'm just relaying what Leonardo is telling the operators when they ask about this SB. That the AAIB have not (as yet) given them any info about possible or probable causes of this accident.

Sycamore, the TR is duplex hydraulic. It is controlled with a single push-pull cable. Unlike previous Leo machines that have relied on control tubes. Hydraulics cannot be selected off as the aircraft cannot be flown without hydraulics.

I know as much as any 169 operator who asks the right questions :)
From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.

Not discernible from the drawing but appears that the shoulder the washer sits on is probably just a bit larger than the hole in the hinge bracket (90). Lack of washer would allow the system to operate normally but might cause high stress on the hinge bracket leading to a fracture. Even without a fracture it could dig a hole in the hinge bracket resulting in play that could cause other issues such as the nut being loose which in turn could cause other damage.

[PEASACAKE]

[QUOTE=MurphyWasRight;10304564]From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.

I have no experience on this helicopter type (but 43 years on many others).

In most mechanical assembly situations a washer is placed "under" a nut, and looks "correctly assembled" when inspected, but it is the opposite in this case.

[Overdrive]

E. DESCRIPTION
Following an in service event, this Service Bulletin requires an urgent check of the proper installation and functionality of the Tail Rotor servo-actuator feedback lever installation and interface on the back end of the component.
Incorrect installation may lead to loss of Tail Rotor control which, depending on the flight condition, could lead to loss of control of the aircraft.
Feedback on the compliance to this Service Bulletin is required
3. Perform a visual inspection of the input lever of the TR servo-actuator:
3.1 With reference to Figure 1 and Figure 2 perform an in situ inspection of the nut (60), the cotter pin (50), the lock-wire and the hinge bracket element (90) connected to the lever feedback link (110) for condition and absence of damage.
3.2 Check the connection elements of the input lever (110) of the TR servo-actuator taking particular care on the lever feedback link.

Murphy, there are possibilities as you suggest. The wording of the SD is perhaps not ideal and certainly doesn't detail any specific potential fault or assembly mistake, and maybe that is for a reason; the intention being to ensure that all ships have the components in place and correctly installed in good condition, not to support speculation about actual cause of the accident. However the SD also doesn't mention that washer with the other components.

Nothing to do but wait...

[Overdrive]

Interesting. As stated in the EAD, perhaps simply a precautionary measure based on what was observed in the accident. It would appear there is though, a way in which the mechanism can be incorrectly installed/assembled that has been either observed or imagined and is causing concern. Of course this may yet not apply in the case of this recent accident.

[sycamore]

Nooby,thanks again...must be using `old newstock `teleflex` from Whirlwind days....

[GrayHorizonsHeli]

you can guarantee they found a missing nut on the accident helicopter at this point.
what they cant guarantee yet is if it was an isolated incident or not. Hence the SB and AD.
this is the data gathering stage where they find out if it's a widespread issue or not.

Ive been reading others posts about the two stages of locking. This is a must on any flight control. Dont forget though that they are only safety nets to the initial locking, which is the correct torque on the nut. Continual inspections offer the final net of safety.

In essence what I am saying is there was 4 failures here.
The torque was lost/incorrect or was never applied, allowing the nut to un-thread.
either faulty cotterpin/lockwire, or missing cotterpin/lockwire the failure was just a matter of time.
and the 4th, the inspections, didn't catch the impending loss.
Personally I think the loss of the nut would have happened quickly once torque was lost and the safety features failed to retain it.

[Misformonkey]

Interesting. As stated in the EAD, perhaps simply a precautionary measure based on what was observed in the accident. It would appear there is though, a way in which the mechanism can be incorrectly installed/assembled that has been either observed or imagined and is causing concern. Of course this may yet not apply in the case of this recent accident.
Lots of components in the TR control system, looks very specific.

[dClbydalpha]

you can guarantee they found a missing nut ...
Personally I think the loss of the nut would have happened quickly once torque was lost and the safety features failed to retain it.

I wonder whether an incorrect assembly, rather than lose a nut, could cause a misalignment or deformation of the link/control rod, resulting in a jamming of the control rod.

[bumpthump]

GRAYHORIZONSHELI Do you actually mean “they found a missing nut” or “they found that a nut is missing”?

I would assume (and surely at this stage of the game, it’s still an assumption) it would be the latter.

I stress again, I am not a pilot, but I am a mech engineer (albeit from a different discipline). As a slight aside, I have used split pins and wire locks on many a track motorcycle in my time, so as well as those two safety measures, there is (as you stated) the correct torque setting for the nut. On top of that, I don’t know if the aviation world use it or not, but on track bikes, it was also common practice to apply a further safeguard in the form of an appropriate thread locking fluid (yes, usually from the Loctite company).

[GeordieMike]

First time poster, long time lurker here!

Hopefully I can answer some of the questions posted about the TRA (Tail Rotor Actuator).

The input lever will drive a dual main control valve to control both hydraulic systems. The position feedback is via the trunnion block (90). I would imagine, and I don’t know this specific actuator, that the control valve will be spring biased to return the actuator to a neutral position if the pilot input is lost. If the position feedback is lost the actuator will run away to a hardover position.

If the washer (140) was incorrectly installed position control would still be present, but the null and full stroke positions of the actuator would be affected . This will be installed and checked (visually and by test) at the manufacturer, as would the nut (60) and cotter pin (50). These parts would never be removed from the actuator unless it was undergoing some repair work (removed from the airframe).

As far as a nut going missing, I think that the thread is handed such that the rotation of the Tail Rotor always tightens the rod into nut. If the nut is missing then I would guess that it was a mechanical failure somewhere.

[9Aplus]

#697 https://www.pprune.org/10304706-post697.html (https://www.pprune.org/10304706-post697.html)

full link of EASA E- AD https://ad.easa.europa.eu/ad/2018-0241-E

[Mike78]

GRAYHORIZONSHELI Do you actually mean “they found a missing nut” or “they found that a nut is missing”?

I would assume (and surely at this stage of the game, it’s still an assumption) it would be the latter.

I stress again, I am not a pilot, but I am a mech engineer (albeit from a different discipline). As a slight aside, I have used split pins and wire locks on many a track motorcycle in my time, so as well as those two safety measures, there is (as you stated) the correct torque setting for the nut. On top of that, I don’t know if the aviation world use it or not, but on track bikes, it was also common practice to apply a further safeguard in the form of an appropriate thread locking fluid (yes, usually from the Loctite company).

As stated in my post earlier in this thread, I am not a pilot. I am however, a groundsman, and have worked in stadium environments on and off for many years. What I can tell you is that if standard post match practices were carried out (they may well not have been, given the circumstances), there is a very good chance that any missing components would have been found, if they were on the pitch itself.

Immediately following matches at this level, pitches are effectively 'hoovered' with mowers to remove debris - this debris includes organic debris i'e., tufts of grass etc, and also objects thrown onto the pitch - coins is the common issue in this respect. If a nut, or other component was on the pitch, it would have been found during the post match 'clean up, or failing that, during the next cut as the mower blades would 'find' it.

I suspect however that all pitch maintenance activities would have been suspended immediately given the nature and location of the incident. That said, if there were any components on the pitch, they would most definitely have been found by now.

[bumpthump]

Those familiar with this particular aircraft have already stated that this particular component requires the removal of a cover for inspection. That being the case, should any component part company from its design location, there is every likelihood that it would be retained by the cover and remain with the aircraft rather than be found on the stadium playing surface. Would that be (yet another) fair assumption?
Again, in terms of scale, I don’t know how big or small this component actually is.

[MurphyWasRight]

First time poster, long time lurker here!
...
...
If the washer (140) was incorrectly installed position control would still be present, but the null and full stroke positions of the actuator would be affected . This will be installed and checked (visually and by test) at the manufacturer, as would the nut (60) and cotter pin (50). These parts would never be removed from the actuator unless it was undergoing some repair work (removed from the airframe).
...
...
Thanks for the input.
What is the approximate full stroke of the actuator relative to the washer thickness? Would the missing washer offset on null and full stroke positions be subtle/adjustable at some other point or clearly way out? In any case it is hard to fathom leaving the factory that way or with missing lock means.

[GrayHorizonsHeli]

As stated in my post earlier in this thread, I am not a pilot. I am however, a groundsman, and have worked in stadium environments on and off for many years. What I can tell you is that if standard post match practices were carried out (they may well not have been, given the circumstances), there is a very good chance that any missing components would have been found, if they were on the pitch itself.

Immediately following matches at this level, pitches are effectively 'hoovered' with mowers to remove debris - this debris includes organic debris i'e., tufts of grass etc, and also objects thrown onto the pitch - coins is the common issue in this respect. If a nut, or other component was on the pitch, it would have been found during the post match 'clean up, or failing that, during the next cut as the mower blades would 'find' it.

I suspect however that all pitch maintenance activities would have been suspended immediately given the nature and location of the incident. That said, if there were any components on the pitch, they would most definitely have been found by now.


dont make the assumption, or imply that i did, that it fell out into the grass. more than likely it stayed within the cowlings, at least until the crash anyways

[Pittsextra]

Here is a question.

Can someone explain the process / thinking around the AD? In so much that the commentary for the reason of the AD says:-

Reason: An accident occurred on an AW169 helicopter, the root cause of which has not been identified and the technical investigation is still ongoing. While the helicopter was on a take-off phase at low forward speed, a loss of yaw control has been observed.

As a precautionary measure, Leonardo issued ASB 169-120 for AW169 helicopters to provide inspection instructions to check correct installation of the tail rotor (TR) servo-actuator

What I don't understand is the aircraft crashes almost 2 weeks ago. If the AD is truly a precautionary element what prompts the thinking of this 2 weeks later? Surely either its a precaution thinking out loud type AD, in which case why not flag earlier? Or they are concerned about something they have seen more recently, in which case why not just say?? It just seems bizarre.

[Pittsextra]

[RIGHT]

Accident happened late Saturday 27th October.
Leonardo release their SB Monday 5th November.
EASA release their EAD Wed 7th November.

Just over a week for Leonardo to react. I guess just evidence gathering between.



Yeah that would be fair but what evidence? The video footage was available almost instantly and so now evidence surely means physical evidence from the accident aircraft or of prior events that have been caught prior to an accident with other in service aircraft. It can't be the former if the narrative around the AD is faithful and if its the latter does that take a week to get out with the commitment of intelligent minds?

It would be incredible if this isn't off the back of something seen or suspected and so why it can't be said more plainly - or indeed co-ordinated via the AAIB goodness knows... Hey Ho.

[MurphyWasRight]

There’s no specific mention of checking the washer in the SB. Only the nut, the pin and the lock wire.
True enough, the reason I was wondering about the washer is that it is the only thing that might not be obvious if misassembled since a washer is often seen under a nut. Of course that does suggest that if it was suspect it would have been mentioned in the AD.

Most likely is that they suspect a fault in the feedback link but may not know exactly what at this stage.
Hard to fathom how pin and lockwire could be missed on assembly so might be a failure.
Here is one scenario: If the lockwire was incorrectly installed could it eventually wear into the locking pin, possibly on the head side?
.

[Echo Romeo]

So much conjecture.....

[SASless]

It is a slow news week....

[Blade Slap]

I think TR blades tend towards zero pitch when uncontrolled. Gazelle definitely did in manual. Lynx as well, albeit with a powerful spring bias unit? Sea King? Is it generic or type specific?

[GeordieMike]

Thanks for the input.
What is the approximate full stroke of the actuator relative to the washer thickness? Would the missing washer offset on null and full stroke positions be subtle/adjustable at some other point or clearly way out? In any case it is hard to fathom leaving the factory that way or with missing lock means.

I don’t know this specific product but I would expect the stroke to be around 50 to 100 mm. the washer would be a small fraction of this.

I don’t think you would be able to adjust the input mechanism to account for the missing component and the result would be a setting should be far enough out to be identified and rectified.

[GeordieMike]

Remember, this is a static component (control servo and feedback link) that transfers the input to the pitch control, there is no loading at this location.


Yes, the servo actuator is static but I think there will be some torque transmitted down the control rod as the attachment (bearing assembly?) from the control rod to rotor pitch mechanism will not have zero friction.

[Chronus]

CAA PAPER 2003/1
Helicopter Tail Rotor Failures is well worth a read. Here are some extracts.

There are two major types of TRF:
a) A TR drive failure (TRDF) is a failure within the TR drive system with consequent
(usually total) loss of TR thrust. Example causes are internal fatigue or external
impact resulting in a broken drive shaft.
b) A TR control failure (TRCF) is a failure within the TR control system such that
normal pilot control of TR thrust has been partially or totally lost. Example causes
are internal wear or external impact resulting in a severed control cable. The
resultant TR applied pitch, or power, could be free to fluctuate, or may be fixed
anywhere between high pitch (HP) or low pitch (LP) setting, including that of the
current trim pitch (TP).
Both of these TRFs are time critical emergencies. The pilot has to identify and
diagnose the TRF type and react with the correct control strategy within a few
seconds (or less), to prevent the aircraft departing into an uncontrollable flight state.
Even if the pilot recovers from the initial transients, yaw (pedal) control will have been
lost and the ability to manoeuvre safely and carry out a safe landing will have been
significantly degraded. The TR and its drive and control systems are clearly flight
critical components and should be designed so that their probability of failure is
‘extremely remote’. The airworthiness design requirements for UK military and civil
aircraft define ‘extremely remote’ as being less than 10-6 [1] and between 10-7 and
10-9 [2,3] per flight hour respectively.

Recovery from the failure transient
For TRDFs, and TRCFs where the post-failure pitch angle of the TR blades is different
from the pre-failure trim position, the immediate effect is a yaw response. That is, (for
anticlockwise main rotors), nose to starboard following a TRDF or LP TRCF, and nose
to port following a HP TRCF. The level of initial yaw acceleration will depend on the
nature of the failure, and the level of yaw rate and attitude build-up will depend on the
forward speed. In hover, an unchecked TRDF will result in the yawing moment from
the main rotor torque reaction spinning the fuselage at rates in excess of 100° sec-1,
perhaps even as high as 150-200° sec-1. Typically, the higher the forward speed, the
lower the yaw rate and attitude excursion as any natural directional stability of the
aircraft will tend to reduce the severity of the motion. However, this is only true up to
some value of sideslip, beyond which it is possible that directional stability can
reverse, resulting in increased yaw rate and attitude excursions. Evidence from the
Lynx TRF AFS trial [5] suggests that the ability of the pilot to successfully manage a
forward flight failure is strongly related to the extent of the initial yaw/sideslip
transient. If this exceeds 90°, then the pilot is unlikely to be able to recover, as the
flight control problem is exacerbated by disorientation; if the yaw rate reduces to zero
below about 30° yaw angle, then the pilot has a much greater chance of recovering
from the failure. Accompanying the yaw excursions will be pitch and roll motion,
which can further increase the risk of disorientation. An additional effect of any roll
attitude transient is an increase in the main rotor disc angle of incidence, leading to
an increased risk of the rotor over-speeding as the pilot reduces main rotor collective
to contain the effects of the failure. The extent of the attitude excursions depends on
the aerodynamic design characteristics of the fuselage and vertical stabiliser, the
resulting directional stability, the type of attitude stabilisation present in the flight
control system and the pilot’s control actions

[sycamore]

Chronus, #3, loss of tail rotor blade ,followed milliseconds later by loss of other blade(s),and probably the gearbox.. The C of G of the a/c will move to somewhere beyond the nose of the a/c ....

[Blade Slap]

Chronus, #3, loss of tail rotor blade ,followed milliseconds later by loss of other blade(s),and probably the gearbox.. The C of G of the a/c will move to somewhere beyond the nose of the a/c ....

How can CG be fwd of nose?

[arizona]

As a former helicopter pilot I experienced three total engine failures in single engine helicopters and three lucky autorotations that saved the day for my pax, me and the company. Most of my helicopter time though is logged in twin engine helicopters, one of which also gave me an engine failure, but that was in level flight and therefore nothing of interest..

With Occam's razor in mind I got to my very own simplified conclusion that this accident started with a tail rotor failure that turned out catastrophic due to no visual recovery in the blurry video. The helicopter’s counter rotation and the engine sound made me think the helicopter descended with high power and high collective all the way to the ground.. The shape of the tail rotor blades on the downed helicopter made me also think that the helicopter hit the ground with the TR not spinning at all due to a TR drive failure… Why wasn’t the pilots able to lower the collective?

[SASless]

Slap,

How can CG be fwd of nose?

That was some British understatement being used.

When you lose the Tail Rotor Blades, Gearbox, and associated items from the very rear of the helicopter....the CG shift is forward...and very significant....causing a strong pitching movement that might exceed the ability of the flight controls to compensate for and thus cause the loss of the aircraft.

[MitchStick]

Yeah that would be fair but what evidence? The video footage was available almost instantly and so now evidence surely means physical evidence from the accident aircraft or of prior events that have been caught prior to an accident with other in service aircraft. It can't be the former if the narrative around the AD is faithful and if its the latter does that take a week to get out with the commitment of intelligent minds?

It would be incredible if this isn't off the back of something seen or suspected and so why it can't be said more plainly - or indeed co-ordinated via the AAIB goodness knows... Hey Ho.

It could be that during the preliminary investigation something was found that could or could't be the main cause so Leonardo as a precaution released the SB.

The investigation is probably far from over and as far as I know no one would release informations until all data has been analysed.

[Chronus]

As a former helicopter pilot I experienced three total engine failures in single engine helicopters and three lucky autorotations that saved the day for my pax, me and the company. Most of my helicopter time though is logged in twin engine helicopters, one of which also gave me an engine failure, but that was in level flight and therefore nothing of interest..

With Occam's razor in mind I got to my very own simplified conclusion that this accident started with a tail rotor failure that turned out catastrophic due to no visual recovery in the blurry video. The helicopter’s counter rotation and the engine sound made me think the helicopter descended with high power and high collective all the way to the ground.. The shape of the tail rotor blades on the downed helicopter made me also think that the helicopter hit the ground with the TR not spinning at all due to a TR drive failure… Why wasn’t the pilots able to lower the collective?

My guess would be because it was a time critical event.
Factors are : Height above ground coupled with the likelihood of occurence at critical moment of transit to forward flight, size of helicopter, twin engines, high rotation speed following TRFand location of site.
Any chance of succesful recovery would have entailed almost instant recognition of TRF, immediate power reduction and simultaneous pitch down for immediate descent and autorotation, which would involve a high ROD and require favourable terrain below. Might be survivable at low height but not so at the sort of height involved in this instance.
I would readily admit I know little about rotary wing, but I understand that they are far less forgiving than their fixed wing sisters. One thing in common must be that with the vertical stab gone on a fixed wing it also spells curtain time, but as in the cases of the JAL123 747 which managed slightly better than AA 587 they seem to keep going for a little longer before the inevitable. With rotary wing the equivalent of no TR means in no time at all the machine assumes the characteristics of a dandelion strung to a brick.
I really don`t think even the most accomplished pilot could have pulled it off. It would have been a far greater miracle than the Hudson one if they had, would be my humble view.

[Jagwar]

One thing in common must be that with the vertical stab gone on a fixed wing it also spells curtain time, but as in the cases of the JAL123 747 which managed slightly better than AA 587 they seem to keep going for a little longer before the inevitable.

Chronus: Is this because of loss of yaw stability or the shift in CG?

[sycamore]

Jag,you will lose your stability in yaw,coupled with the C OF G change; you might be able to crowd pax into the back to restore/mitigate the CG PROBLEM.The a/c if disturbed in yaw or roll will probably start Dutch -rolling which will require a lot of handling skills,especially during any configuration changes,and approach/landing....or may not.. A B52 lost it`s fin/rudder and landed safely-see u-tube..

Slap,in my case of t/r and gearbox departure ,the change of CG was about 3" forward of the Fwd limit,`past my nose, anyway`!! The stick has reached the back-stop ,and the a/c has changed direction by about 50-60*;entering autorotation and chopped the engine leads to a further pitch down ,but there is a `pimple` of a hilltop with cleared scrub that we are pointing at.
To flare requires another quick fwd stick and back again with lever,as it`s also uphill,but at zero groundspeed.Landed upright,but burst a main tyre on a treestump.. ...There is a pic on `Rotorheads around the World-views from cockpit(not video) ,page 15....

[tottigol]

Slap,



That was some British understatement being used.

When you lose the Tail Rotor Blades, Gearbox, and associated items from the very rear of the helicopter....the CG shift is forward...and very significant....causing a strong pitching movement that might exceed the ability of the flight controls to compensate for and thus cause the loss of the aircraft.

That is not always the case SAS, I agree on the forward shift, however actual CG position at time of accident is a big part of the equation.
You can PM me and we can talk the details.

[AMDEC]

Statistically there are many more accidents due to unanticipated yaw -- so poorly named as LTE -- than due to TR failures. Looking at the initial yaw, there is no abrupt acceleration. If it is a TR failure, I guess you have to look for a very progressive failure...
AAIB investigations will say it.

[Thomas coupling]

The reference datum is a reference plane that allows accurate, and uniform, measurements to any point on the aircraft. The location of the reference datum is established by the manufacturer and is defined in the aircraft flight manual. The horizontal reference datum is an imaginary vertical plane or point, placed along the longitudinal axis of the aircraft, from which all horizontal distances are measured for weight and balance purposes. There is no fixed rule for its location, and it may be located forward of the nose of the aircraft. For helicopters, it may be located at the rotor mast, the nose of the helicopter, or even at a point in space ahead of the helicopter. While the horizontal reference datum can be anywhere the manufacturer chooses, most small training helicopters have the horizontal reference datum 100 inches forward of the main rotor shaft centerline. This is to keep all the computed values positive. The lateral reference datum is usually located at the center of the helicopter. .................................

[TeeS]

That’s the datum TC, not the C of G.
Cheers
TeeS

Just realised that was a quote but can’t find where it was from, sorry if I misunderstood the point of your post.

[Mee3]

You will not have "CG move in front of the nose" even you lose the TR while keeping the H stab. Thats BS unless helicopter had been loaded nose heavy anyways. Most of the weight are lining up with the MGB and the moment of inertial will hard to overcome. FM says it all.

[HarryMann]

From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.

Not discernible from the drawing but appears that the shoulder the washer sits on is probably just a bit larger than the hole in the hinge bracket (90). Lack of washer would allow the system to operate normally but might cause high stress on the hinge bracket leading to a fracture. Even without a fracture it could dig a hole in the hinge bracket resulting in play that could cause other issues such as the nut being loose which in turn could cause other damage.

MWR ... If you are in any way correct, this implies a really poor original design... a prime goal in mechanical components design just as important as stessing and robustness is clarity of assembly whilst minimising potential for mis-assembly...
e.g. all bolts in a locality doing much the same job being of the same length, usually arranged by say stepping a casting thickness .. EVEN IF IT COSTS WEIGHT..

[tottigol]

You will not have "CG move in front of the nose" even you lose the TR while keeping the H stab. Thats BS unless helicopter had been loaded nose heavy anyways. Most of the weight are lining up with the MGB and the moment of inertial will hard to overcome. FM says it all.

Nailed it!

[DOUBLE BOGEY]

Nailed it!

He has not really "Nailed" it. the "Unless" statement is still hogwash.

To have the CG in front of the nose of the helicopter, you would need a MRB sticking over nose, the portion beyond the nose, weighing more than the entire helicopter behind it.

To keep this sensible and simple, The Helicopter CG should be directly under the Main Rotor Mast centroid both Longitudinally and Laterally. That's the optimum ideal position giving 100% MR flight control in all directions.

However, practically speaking, there has to be some loading of the helicopter which would cause the CG to move around the rotor centroid. It cannot move that much. Even in a large helicopter like an EC225 it can only move 0.5m longitudinally.

There are limits to how far the CG can move away from the rotor centroid before effective flight control is compromised.

If the TRGBX and its blades depart the airframe, the CG will make a significant move forward. It is highly likely in ALL helicopters that this will result in a significant compromise of the forward CG limit and effective aft cyclic to counter the forward movement of the CG will reach the aft stop before the pitch moment forward can be cancelled. The results.....well not pretty.

The Datum, as someone has already posted, is simply a point in space to facilitate all calculations to be in the positive range. Usually it is quite a way out in front of the helicopter nose to facilitate the fitment of long PITOT probes during certification. For simplicity, it remains there. Therefore, the limits for longitudinal CG are expressed in positive numbers and to keep the theme at the EC225 4.4m to 4.9m. This actually means, behind the datum. Not in front of the rotor centroid.

I know 99% of Rotor heads know this but to clear up the incessant garbage postings by the odd individual who seems confused....enjoy!

[Fareastdriver]

The only occasion I know off where the main door departed into and then removed the tail rotor assembly resulted to a massive pitch down which the pilot tried to correct with aft cyclic. The caused the main rotor, in sympathy with the pitch up of the tail boom to slice off the boom just aft of the mounting point.

The ensuing pandemonium resulted in the aircraft descending almost vertical and killing everybody on board.

[SASless]

Bristow lost a 412 in Nigeria and the evidence showed a Cabin Door had come into contact with the Tail Rotor.

The flight was at night in IMC weather.

The aircraft and occupants were not recovered as I recall.....just some odd bits and pieces.

A ROV was lost on the first dive and the search was called off afterwards.

[Oldlae]

Bristow lost a 212 in the Sumatran jungle when the T/R departed in the cruise with half of the 90 box. The T/R was not found within a few hundred yards of the crash site. It later found by some Indonesians who were paid a lot of rupiahs, the distance from the locus could not be determined. The rotor was examined by the AAIB and it was determined that it had been hit by an oil cooler duct. The aircraft had caught fire and the port side was burnt out but the starboard panel was still attached. It was assumed that a faulty catch on the panel had failed and the panel had flown over the tail boom and hit the rotor.

[sycamore]

For; Blade Slap,totti,M3- perhaps I should have put the phrase about the CG` beyond the nose`` in italics/commas,or a couple of smilies.It was meant to imply that the loss of a tail-rotor and gearbox will have a very significant FWD C o G change,irrespective of where it was originally,and if it was FWD AT THE TIME you will get a significant NOSE DOWN pitch.
In my case ,I had 2 engineers at the front of the cabin,looking at the rear of the engine and reduction g.box checking for oil leaks,as we had just done an engine out,change a component /pipe on the back of the gearbox,, engine back in,and RTB.,so my CoG was well Fwd anyway.
I might suggest if you are pilots or gingerbeers that you go ,find the appropriate tech manual which shows all the weights for tailrotor ,g/box,etc and work out the resultant change of C o G ,if they should depart,......
SAS,DB, thanks....

[tottigol]

For; Blade Slap,totti,M3- perhaps I should have put the phrase about the CG` beyond the nose`` in italics/commas,or a couple of smilies.It was meant to imply that the loss of a tail-rotor and gearbox will have a very significant FWD C o G change,irrespective of where it was originally,and if it was FWD AT THE TIME you will get a significant NOSE DOWN pitch.
In my case ,I had 2 engineers at the front of the cabin,looking at the rear of the engine and reduction g.box checking for oil leaks,as we had just done an engine out,change a component /pipe on the back of the gearbox,, engine back in,and RTB.,so my CoG was well Fwd anyway.
I might suggest if you are pilots or gingerbeers that you go ,find the appropriate tech manual which shows all the weights for tailrotor ,g/box,etc and work out the resultant change of C o G ,if they should depart,......
SAS,DB, thanks....
Not all aircraft are affected the same, it seems that the 212/412, perhaps the H-1 series and civilian counterparts suffer the most.
I am aware of more than one 407 TRGB and a portion of tailboom departures back in '98/2000 where a successful autorotation was made at least once to the water (PHI GoM 1998 or '99) with a full load of passengers, the pilot reported no excessive pitch down moment.
As far as consulting the appropriate tech manuals, I have access to a couple of types (which I cannot disclose) and we ran calculations confirming that the loss of the TRGB and the TR blades does not move the CG forward to a catastrophic unrecoverable value.
HTH

[sycamore]

Totti, OK,I`ll` add a couple of other bits as your calculator is warmed up;
IF the helo now enters a full autorotation,how much aft stick movement is produced at a variety of airspeeds,to keep a level attitude;
now do it all at a fwd C o G...
now consider the fact that the aircraft has yawed(depending on airspeed and fin size)which may also have a `pitch` effect..
now consider where the stick/disc relationship is to tail- boom.....and your stick margins vs control stops

Answers on a postcard,,,...or sheets of A4.....

[[email protected]]

Not rocket science to suggest that the longer the tailboom, the further from the C of G is the TRGB and the more marked effect its loss will have on longitudinal C of G.

[tottigol]

Totti, OK,I`ll` add a couple of other bits as your calculator is warmed up;
IF the helo now enters a full autorotation,how much aft stick movement is produced at a variety of airspeeds,to keep a level attitude;
now do it all at a fwd C o G...
now consider the fact that the aircraft has yawed(depending on airspeed and fin size)which may also have a `pitch` effect..
now consider where the stick/disc relationship is to tail- boom.....and your stick margins vs control stops

Answers on a postcard,,,...or sheets of A4.....
I don't need to calculate anything,read my post again.
Crab, you are absolutely correct.

[MurphyWasRight]

MWR ... If you are in any way correct, this implies a really poor original design... a prime goal in mechanical components design just as important as stessing and robustness is clarity of assembly whilst minimising potential for mis-assembly...
e.g. all bolts in a locality doing much the same job being of the same length, usually arranged by say stepping a casting thickness .. EVEN IF IT COSTS WEIGHT..

Totally agree, I sincerely hope that my conjecture on misplaced washer is way off. I mentioned it only because at least as presented in the AD it is hard to see how both the split pin and lockwire could be missing without being noticed and was pondering what else could be mi-assembled.

GeordiMike also responded that lack of washer would likely affect the centering of the control system enough that it would at least be noticed if not totally unserviceable.
(My thoughts based on his feedback)

Again most likely they suspect something in that mechanism but do not know (or cannot say with certainty) exactly what so the goal is to have it looked at for anything suspicious.

[Hot and Hi]

For; Blade Slap,totti,M3- perhaps I should have put the phrase about the CG` beyond the nose`` in italics/commas,or a couple of smilies.
Dont worry, that was blatantly clear to anybody who didn’t bother to respond.

[GrayHorizonsHeli]

From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.

Not discernible from the drawing but appears that the shoulder the washer sits on is probably just a bit larger than the hole in the hinge bracket (90).


did you magnify the photo?
If you haven't, please do. I see the arrangement in the photo as indicated in the drawing.

[MurphyWasRight]

Quote:
Originally Posted by MurphyWasRight https://www.pprune.org/images/buttons/viewpost.gif (https://www.pprune.org/rotorheads/614822-helicopter-down-outside-leicester-city-football-club-not-condolences-post10304564.html#post10304564)
From the picture it seems improbable that both locking means were missing/misinstalled.
There is a more subtle issue of the effects of the washer (140) either missing or on the wrong side. This would not jump out on a visual inspection like missing locking means would.

Not discernible from the drawing but appears that the shoulder the washer sits on is probably just a bit larger than the hole in the hinge bracket (90).
did you magnify the photo?
If you haven't, please do. I see the arrangement in the photo as indicated in the drawing.
I saw that the photo matches the drawing as expected since the photo is of a correct assembly. My question was about possibility of an incorrect assembly with the washer on the wrong side, under the nut, and if that was even possible without causing an obvious problem. If it is possible then the hardened rod shoulder could stress the 'hinge bracket element (90)' and cause a failure,especially if the shoulder was significantly smaller than the outside diameter of the washer.

Without detailed drawings and system knowledge whether misassembly is even possible is an open question though feed back from GeordiMike suggests it probably would be obvious due to offsets in the servo loop.
Also if washer misplacement (or missing) is possible seems that it would have been an explicit check in the AD which does not mention the washer.
Then again something did go wrong, as others have said will be clear in final report.

[GrayHorizonsHeli]

thats why I asked, I figured that as well, if the washer was suspect for any reason it would be part of the AD.

Incidentally for simple random information totally unrelated to this case, I was disassembling some AS350 control rods today, and while cutting the lockwire, the nut started turning. the lockwasher design didn't stop the nut as it was just a place for the lockwire to terminate.
The "double locking" in this case did its job although the proper torque was not on the nut.
However, nothing further would have happened because the lockwire, torgue and locktabs, on the other end would have all had to fail too before bad things happened.

[OnePerRev]

thats why I asked, I figured that as well, if the washer was suspect for any reason it would be part of the AD.

Incidentally for simple random information totally unrelated to this case, I was disassembling some AS350 control rods today, and while cutting the lockwire, the nut started turning. the lockwasher design didn't stop the nut as it was just a place for the lockwire to terminate.
The "double locking" in this case did its job although the proper torque was not on the nut.
However, nothing further would have happened because the lockwire, torgue and locktabs, on the other end would have all had to fail too before bad things happened.

This is a dangerous assumption, in part led by a pervasive culture that safety wire, cotter pins, etc. actually help keep a joint together. Proper torque keeps it together, and absence of torque can lead to high loads from vibration even on parts that are not thought of as load carrying, wear on threads can be just as bad and can lead to loss of control. That rod should be replaced, or possibly NDI inspected for damage, but at minimum raise awareness... do not ignore "loose nuts found on good parts".

earlier posters describe uncommanded full actuation which would certainly be possible probably likely, with failures on the subject side of servo. A neutral tail rotor would not cause aircraft to keep spinning after main rotor torque was dropped, it would slow down, and if biased it would actually turn the aircraft to the left. Yes, a missing nut could do this, but for all we know, they found a fractured end of servo. One cause of that could be... incorrect or inadequate torque on the nut. An initial inspection is prudent.

[RVDT]

Further to OPR's comments -

Certification Specifications contain the following statement -

Fasteners

(a) Each removable bolt, screw, nut, pin or other fastener whose loss could jeopardise the safe operation of the rotorcraft must incorporate two separate locking devices.
The fastener and its locking devices may not be adversely affected by the environmental conditions associated with the particular installation.

(b) No self-locking nut may be used on any bolt subject to rotation in operation unless a non-friction locking device is used in addition to the self-locking device.



At the outset this seems to be prudent and simple but there are other subtleties. Installation of locking devices implies that someone has made the effort to install things correctly and
when doing a "duplicate inspection" the second inspector can at least see that the locking is in place.

As quoted by OPR the locking devices do NOT have anything to do with the integrity of the fastener. If the fastener has become loose and it is relying upon the locking device
something is wrong with the connection and the safety system works.

There are numerous issues that safety locking can overcome and incorrect torque is only one of them.

Incorrect hardware
Worn hardware
incorrect assembly of the fastener etc etc.

Nuts and bolts can be more complex than a lot of people appreciate.

I know of one particular large manufacturer who does not comply with the above statement but that is another story.......................

[Diesel_10]

FAA Follows EASA with Stricter AW169 Emergency ADby Mark Huber (https://www.ainonline.com/mark-huber)
- November 9, 2018, 1:49 PMThe FAA has issued a more comprehensive Emergency Airworthiness Directive (AD 2018-23-52) to cover Leonardo AW169 and AW189 twin-engine helicopter tail rotor servo-actuator assemblies, following the issuance of an EASA Emergency AD earlier this week. The FAA said it “determined the unsafe condition exists and is likely to exist or develop on other helicopters of the same type design.”

The FAA Emergency AD requires inspecting the nut, cotter pin, lock-wire, hinge bracket connected to the tail rotor servo-actuator feedback lever link, and each connection of the tail rotor servo-actuator feedback lever link. It also requires applying a paint stripe or torque seal on the nut and reporting certain information to Leonardo.

The EASA AD specifies visually inspecting the nut, cotter pin, lock wire, and hinge bracket for condition and absence of damage, while the FAA Emergency AD requires inspecting those parts for correct installation and loose, broken, and missing parts. While the EASA AD specifies visually inspecting the connection elements of the tail rotor servo-actuator feedback lever link, the FAA Emergency AD requires inspecting all three connections of the tail rotor servo-actuator feedback lever link for correct installation and loose, broken, and missing parts. The inspections specified by the FAA Emergency AD are not limited to visual inspections.

The EASA AD requires contacting Leonardo for approved instructions if there is any damage or other finding, while the FAA Emergency AD requires performing any necessary repairs in accordance with FAA-approved procedures. The FAA AD covers seven helicopters on the FAA registry and estimates the cost of compliance at $255 per helicopter. Leonardo has produced approximately 70 AW169s and 55 AW189s to date.

[212man]

No real news but AAIB special bulletin....
https://assets.publishing.service.gov.uk/media/5bebe118e5274a083e73dc27/S1-2018_G-VSKP.pdf

[beamender99]

The helicopter ....... did not respond to the pilot's command, initial findings show.

https://www.bbc.co.uk/news/uk-england-leicestershire-46208494

[CyclicRick]

BBC news just posting that the "helicopter did not respond to pedal inputs".
Beat me to it.

[DOUBLE BOGEY]

Its is interesting that the Landing Gear was retracted! On a structure RFM profile should this not be done at Vy + 200 feet?
The aircraft impacted upright. If the gear was down maybe some energy would have been absorbed......maybe it would not have rolled!

[GrayHorizonsHeli]

I think landing on the stone wall/fence was the deciding factor to the aircrafts eventual resting place, regardless of gear up or down.

[Sir Niall Dementia]

I think landing on the stone wall/fence was the deciding factor to the aircrafts eventual resting place, regardless of gear up or down.

And the gear speed restrictions tend to make most people hoik it up pretty quick.

SND

[212man]

And the gear speed restrictions tend to make most people hoik it up pretty quick
Interesting, as without doors you would not associate that kind of gear with a IAS low restriction - is it because it's electrically actuated?

[asdf1234]

Interesting that after loss of TR authority, the aircraft continued to climb. Why would the pilot increase the power when he lost the TR?

[212man]

Interesting that after loss of TR authority, the aircraft continued to climb. Why would the pilot increase the power when he lost the TR?

I would guess at an involuntarily input caused by either the startle factor or bio-mechanical due to the sudden forces being experienced. It wasn't much.

[Fareastdriver]

involuntarily input caused by either the startle factor

Who was actually flying it?

[G0ULI]

Fareastdriver

Given that the AAIB report refers to four passengers and one pilot, and states that the aircraft failed to respond to the pilot's pedal inputs, the answer is obvious.

[dClbydalpha]

Interesting that after loss of TR authority, the aircraft continued to climb. Why would the pilot increase the power when he lost the TR?

I'd assumed that collective increase was part of the initiation of the next manoeuvre and was accompanied by a pedal input to anticipate the increase in torque. In this case only one happened and the aircraft climbed for a short time.

[asdf1234]

I'd assumed that collective increase was part of the initiation of the next manoeuvre and was accompanied by a pedal input to anticipate the increase in torque. In this case only one happened and the aircraft climbed for a short time.

The AAIB reports are always concise in their use of language and never leave room for ambiguity of interpretation. If the climb was as a result of the transition procedure they would either omit the climb event or positively correlate the climb to the transition procedure . They mention the climb subsequent to the TR loss of authority because it is an event of interest to them .

​​​

[Cows getting bigger]

Indeed. They do not mention a "collective increase", they merely state that the climb paused and then continued. There is implication that the pause was coincident with pedal movements and associated (correct) yaw which then became yaw that did not reflect the pedal demand.

Head scratch moment - if the tail rotor demand reduces, the system sends more to the main rotor. Remember the collective/pedal interaction?

[dClbydalpha]

Indeed. They do not mention a "collective increase", they merely state that the climb paused and then continued. There is implication that the pause was coincident with pedal movements and associated (correct) yaw which then became yaw that did not reflect the pedal demand.

Head scratch moment - if the tail rotor demand reduces, the system sends more to the main rotor. Remember the collective/pedal interaction?

They don't mention collective at all, but there must have been some at some point.

Rather than deduce the pilot was "startled" does it make more sense that the climb was due to a pre-planned manouevre? One which required the application of collective, but was aborted due to the lack of yaw control? How long would it take for him to realise he didn't have yaw control, does this amount to about 100ft?

What feedback would cause loss of tail rotor to send more to the main rotor? Are you thinking an automatic increase in collective pitch, or an ungoverened increase in Nr?

[DOUBLE BOGEY]

T
What feedback would cause loss of tail rotor to send more to the main rotor? Are you thinking an automatic increase in collective pitch, or an ungoverened increase in Nr?

I feel this is dead herring!

If the TR Pitch reduces (reduction of effective thrust) drag reduces accordingly. This would momentarily cause the NR to increase as now power available exceeds power demand for Nr Nominal 100%. However, the FADECS would sort this out really quickly. In any case, a slight momentary increase in NR will not correspond to an immediate and somewhat sustained climb.

Other than that I cannot see any other correlation between the Yaw Channel (failed) and the collective moving involuntarily unless the mixing unit was somehow stuffed.

[RVDT]

However, the FADECS would sort this out really quickly.

Or maybe not - appreciate that the FADEC has inputs from control positions i.e. collective and TR pitch, torque, and atmospheric data and that is mapped inside the ECU to a fuel flow required to achieve the net result.

Actual speed governing might not be a good as "normal" if you had a full left pedal input to the ECU with no resulting increase Q load from the TR would probably give you an unintended result.

NR is normally referenced to the current DA and speed is governed by pre-empting the relationship between CLP and TR pitch. Quite often with CLP and TR pitch inputs are attached to either end of an LVDT (Linear Variable Displacement Transducer) and this value via the map in the ECU will give you a fuel flow pretty close to that required without being reactive to a change in NR.

Current FADEC controlled engines are great. They are also great at masking the true characteristics of the main rotor. When the FADEC is removed from the loop (autorotation) many are surprised at how "lively" the main rotor is to RPM. control.

Loss of input data will normally give you a "DEGRADE" warning but more likely not in this case.

[helicrazi]

Who has tried this profile in the sim yet with a TR failure at the same point?

anyone get away without a red screen?

[[email protected]]

Surely the 'pause' in the climb is as a result of selecting an accelerative attitude at TDP.

Also, if you think you have a control problem at night at a critical stage of flight, I would suggest the natural reaction would be to get away from the ground while you sort it out.

[DOUBLE BOGEY]

Surely the 'pause' in the climb is as a result of selecting an accelerative attitude at TDP.

Also, if you think you have a control problem at night at a critical stage of flight, I would suggest the natural reaction would be to get away from the ground while you sort it out.

From the preliminary AAIB report:
"The helicopter then began a climb on a rearward flight path2 while maintaining a northerly heading. Gear retraction started as it passed through a height of approximately 320 ft. The climb then paused. Heading changes consistent with the direction of pedal movements were recorded initially, then the helicopter entered an increasing right yaw contrary to the pilot’s left pedal command. The helicopter reached a radio height3 of approximately 430 ft before descending with a high rotation rate."

There seems to have been an increase of 110 feet RADALT after the TR event. However, as someone pointed out, the surface beneath the helicopter is not even so it could also be a Red Herring.

[helicrazi]

From the preliminary AAIB report:
"The helicopter then began a climb on a rearward flight path2 while maintaining a northerly heading. Gear retraction started as it passed through a height of approximately 320 ft. The climb then paused. Heading changes consistent with the direction of pedal movements were recorded initially, then the helicopter entered an increasing right yaw contrary to the pilot’s left pedal command. The helicopter reached a radio height3 of approximately 430 ft before descending with a high rotation rate."

There seems to have been an increase of 110 feet RADALT after the TR event. However, as someone pointed out, the surface beneath the helicopter is not even so it could also be a Red Herring.

Could just be the drop off of the stadium

[industry insider]

1837 Arrived at the helicopter, 1844 lifted off - 7 minutes for a walk around, climb in, pre-start checks, 2x engine start and lift off.

At the ground, Started up (power on probably to start the system recording) at 1934 and lifted off at 1937.

Seems to have been in a bit of a hurry?

[SASless]

Three minutes to start up and reach Take Off RPM.....not a rush job in modern Twins with FADEC's.

As the Pilot had flown the aircraft on several sectors that day already....there is no requirement for a full run-up systems checks.

If the radios and and nav systems had been pre-tuned and set up for the intended flight....it would just be a matter of turning them on.

To make a point about "time"....I once worked a job where we had to be airborne within two minutes of the Alert Klaxon sounding....and that included up to a fifty yard dash to the helicopter.

That is rushed.....sitting in the aircraft and strapped in and ready to hit the Battery Switch....three minutes is not.

[[email protected]]

From the preliminary AAIB report:
"The helicopter then began a climb on a rearward flight path2 while maintaining a northerly heading. Gear retraction started as it passed through a height of approximately 320 ft. The climb then paused. Heading changes consistent with the direction of pedal movements were recorded initially, then the helicopter entered an increasing right yaw contrary to the pilot’s left pedal command. The helicopter reached a radio height3 of approximately 430 ft before descending with a high rotation rate."

There seems to have been an increase of 110 feet RADALT after the TR event. However, as someone pointed out, the surface beneath the helicopter is not even so it could also be a Red Herring. the report highlights the 430 as being radio height but not the 320 so I wouldn't set too much store in the accuracy of the comparison - it may be they are both rad alt heights but maybe not - ADC perhaps?

Much like the footnote at the beginning that specifies the timings are approximate since they come from a variety of unverified sources. Trying to come to accurate conclusions based on potentially inaccurate information is folly.

[DOUBLE BOGEY]

Much like the footnote at the beginning that specifies the timings are approximate since they come from a variety of unverified sources. Trying to come to accurate conclusions based on potentially inaccurate information is folly.

Agreed. The most significant bit of information is the gear being raised at an unusual point in the profile.

[industry insider]

Three minutes to start up and reach Take Off RPM.....not a rush job in modern Twins with FADEC's.

As the Pilot had flown the aircraft on several sectors that day already....there is no requirement for a full run-up systems checks.

If the radios and and nav systems had been pre-tuned and set up for the intended flight....it would just be a matter of turning them on.

To make a point about "time"....I once worked a job where we had to be airborne within two minutes of the Alert Klaxon sounding....and that included up to a fifty yard dash to the helicopter.

That is rushed.....sitting in the aircraft and strapped in and ready to hit the Battery Switch....three minutes is not.

But that was probably in the military. Many of us have done scramble type jobs. This was not, it was a passenger carrying flight into London Stansted. I will agree to disagree with you on the 3 minutes from start to airborne. But 7 minutes for an aircraft that had been shutdown and unattended for 3.5 hours seems quick to me.

[DOUBLE BOGEY]

Extract from report into AS355 TR Control Failure over Cardiff G-SAEW, Flown by an ex student of mine:

The helicopter had been hovering in the area for about 10 to 15 minutes, facing in a south-westerly direction, when it suddenly made an uncommanded yaw to the left through some 180 degrees. The pilot immediately applied full right yaw pedal to counter this yaw. However, although the helicopter stabilised for a moment, it then yawed more rapidly to the left. At this time he called out to the two observers on board to warn them of a problem with the helicopter. He partially lowered the collective lever in an attempt to regain control and applied some forward cyclic to gain forward motion and airspeed, but the helicopter then entered a steeply spiralling/yawing descent to the left. The pilot realised that he would not be able to recover full control of the helicopter and abandoned his attempt to fly out of the situation. He concentrated on keeping the helicopter as level as possible whilst looking out through the right side window for visual reference, since he found the forward view too confusing due to the rapid yawing motion. He adjusted collective to achieve what he judged to be the best combination of rate of descent against yaw, and when he caught sight of the surface in his peripheral vision he pulled the collective lever fully up to cushion the impact.
The helicopter came to rest embedded in the roof of a house, as shown in Figure 1, having broken through the rafters and settled in a right side low attitude. After the impact, the pilot was unable to reach the engine fuel controls on the overhead panel until he had unstrapped himself from his seat. However, when he was able to reach the speed select and emergency fuel shut off levers he could not move them due to impact induced distortion of the overhead panel. He was able to activate both fire extinguishers and to turn the battery switches OFF. The observer in the front left seat escaped through his door on the left side of the helicopter and the rear seat observer climbed past the pilot and exited through the same door; the pilot then followed. The three occupants, all of whom were wearing protective helmets, were uninjured and later used a ladder to climb down from the roof.

A considerable amount of skill and quick thinking with Lady Luck for the impact. That boy did well!

[SASless]

Insider....twas not a military gig....but involved guarding some very high value items.

What is magic about the aircraft being shut down and unattended for 3.5 hours?